I'm the guy who developed the S-video mod as described in the Denial wiki. While I never made any attempts to improve the composite output, I can give some explanations and suggestions you might find of value. Firstly, the red trimmer adjusts the colour subcarrier frequency, if it is incorrectly adjusted, you may get 'Hannover Bars' in coloured areas. You can see an example of those in the bottom two images in the Denial S-video wiki page. If the adjustment is off by too much, the colour may completely drop out. This applies to PAL. NTSC does not have the 180 deg alternate phase reversal, so if this trimmer is out of adjustment, the colours will all be wrong. The key to maximum video quality is correct video levels. Firstly, your TV/monitor should be presenting a 75 ohm load to the input video signal. The video should be 1 volt, measured between the bottom of the sync pulse and the white level. This is adjusted with the trimpot as you describe in the video. Additionally, with the entire video signal at 1 volt, you should have 0.3 volts between the bottom of the sync pulse and black level. This relationship is fixed within the VIC chip. The colour level should be at 0.3 volts peak-to-peak on the colour burst signal. There is no means to adjust this in an unmodified VIC-20 and it is normally way too high. This is why you get the serrated edges between different coloured areas. It is actually called 'Dot Crawl'. Normally on a proper interlaced video signal, these dots will slowly crawl up or down, but on a VIC-20 they are stationary. You will never be able to eliminate dot crawl, however it can be reduced by two methods. The first method is to reduce the colour level to at least the correct 0.3 volts. You could reduce the colour level further, which will further reduce dot crawl, but you will eventually get to a point where the colour will get noisy or blurry or even become prone to dropping out. The second method (and which is possibly what is happening in your modification) is to restrict the low frequency bandwith of the colour signal (before it is combined with the luminance signal). This will have the side effect of smearing the colours somewhat, and may even cause some smearing of the luminance signal too. Your LCD monitor would most likely have a comb filter in it which is a far more sophisticated method of separating the chrominance from the luminance. This almost entirely eliminates dot crawl as you have observed. Your CRT monitor would use the old bandpass filter method which is far less effective. Finally, I have noticed there is an amazing variation in picture quality between different VIC chips. Often these are temperature sensitive. I have one VIC chip that gives an OK image when cold, but after a while the blue parts of the image go all noisy, blurry and are full of 'jailbars' once the chip warms up.
Excellent information. Thanks! When I revisit this VIC-20 (which I'll have to because it gives you weird diagnostic errors), I'll have another look at the signal with your information. Thanks!
Hello @a4000bear Thank you for your very useful comment which reinforces the choice I recently made with my Vic20, namely that it is the type of monitor which above all allows for optimal image quality. Soon I'm going to pick up a Panasonic Plasma TV (TH-42PV500) screen (used for €70). I will first plug the Vic20's S-VIDEO SCART cable directly into the Panasonic Plasma TV to see the result. Then, I will use a converter (active/5v USB-C power supply) by connecting the S-VIDEO SCART socket of the Vic20 to the SCART input of the converter and at the output of the converter the RCA / RGB socket to the Panasonic TV screen in Plasma. My converter allows adjustment of RGB colors using three potentiometers if necessary. According to my analysis, I will not need to modify the hardware part as was done in this video by @NoelsRetroLab PS: I have two VIC20s for this test, a British Vic20 and a German VC20 (very rare Vic20 model)
D00d! Correlating the O Scope with the screen capture, AND showing the probe points on the schematic. Winning! This is some of the most effective signal level description of a computer system I've seen. Excellent, and thank you!
Thanks,I thought it was just my old tv set.Now watching your vic20 stuff before attempting my repairs.These are the most useful of all the offerings on youtube on this subject so far.
That was really great! The VIC 20 doesn’t get enough love from the retro community. I’m currently trying to recreate my original setup at the moment - just the expansion slot extender, joystick and one game to go before I have exactly what I had as a kid (except it’s NTSC instead of PAL).
I've just done this to my Vicky Twenty and I'm blown away by the result. It took a bit of figuring out because that board doesn't have the 'original' position of C13 marked, so I just had to figure out where to solder that cap. The rest of the mod was just the same. It's perfect for me. I had been planning to make the s-video mod but didn't like the idea of having a dangling s-video cable, or fitting an s-video socket. This is perfect, I just use the original video socket as before. Thank you so much!
With most cartridges, it is possible to position the „active area“ of the screen output with the cursor keys. So, the monitor being in the upper left corner is not a thing, you have to live with.
I have a SCART adapter just like you shown at 15:22 and I sacrificed its plastic case in the name of science. And I was surprised to find out that chroma and luma signals from the S-video connector go to 2 different pins on the SCART connector. Whether or not your TV would to make anything out of it, of course, depends entirely on the TV.
I am guessing that there are at least the two versions, one that creates a composite signal and one that keeps chrominance and luminance apart. Why not simply try a beeping multimeter for signal continuity and the SCART pinout... en.wikipedia.org/wiki/SCART
Hi Noel, I've just performed the same surgery on my newly acquired VIC-20 (PAL version), but I'm getting a yellow shadow on the left hand side of the letters. Same power up display as yours at 20:55 The display is far better than it was though, so is certainly a vast improvement. Edit: I've improved it even more. After some experimentation, I went back to the beginning and removed the 470N cap and just replaced the ferrite bead (or 100n cap) with a 2K resistor. I've introduced an RC network in effect. 2K ohms value was chosen using a test 10K potentiometer. All yellow shadows have completely gone now. I'm really pleased I found your video. Many thanks.
The usual way to get rid of that ringing is to put a low value damping resistor in parallel with it, you'll often find that done with a coil wound onto a resistor in CRT gun drivers, if you remove the resistor or it goes open circuit then you get ringing and smearing on screen.
That makes sense. That's what I had read too. Any idea why they put it there in the first place? The C64 and VIC-20 are full of those ferrite beads everywhere!
@@NoelsRetroLab Engineers at the time assumed this would reduce the noise just like it often does with digital signals. If you look at the design on C64 boards, those of 1982/1983 also have ferrite beads. They disappeared on boards 250425 (1984) and afterwards.
Except ferrite beads are generally lossy. They appear resistive at high frequencies. It shouldn't cause ringing like a true inductor would. (However, it sure looks like it is from looking at the output on screen.)
Hello, Thank you for your very useful comment which reinforces the choice I recently made with my Vic20, namely that it is the type of monitor which above all allows for optimal image quality. Soon I'm going to pick up a Panasonic Plasma TV (TH-42PV500) screen (used for €70). I will first plug the Vic20's S-VIDEO SCART cable directly into the Panasonic Plasma TV to see the result. Then, I will use a converter (active/5v USB-C power supply) by connecting the S-VIDEO SCART socket of the Vic20 to the SCART input of the converter and at the output of the converter the RCA / RGB socket to the Panasonic TV screen in Plasma. My converter allows adjustment of RGB colors using three potentiometers if necessary. According to my analysis, I will not need to modify the hardware part as was done in this video. PS: I have two VIC20s for this test, a British Vic20 and a German VC20 (very rare Vic20 model)
Thanks Noel! That's fantastic...I've managed to do it! And now I have kind of a "HiRes" Vic20. No fear of destroying my nostalgic memory: I prefer to feel my Vic20 still "alive" and so evolving :-) Your video had been a milestone for my 'relationship' with it! :-) Much appreciated!
Awesome video as usual Noel. I agree with other comments that the VIC-20 doesn't nearly as much attention as it deserves. This video has made me check the hires mode on my own VIC-20, a very early one with PET style keys, and I'm happy to report that the video output looks exactly like your one with the properly working VIC chip does - phew!
Yay! Good thing because I don't think there are easy replacements for the VIC chip yet, although some projects are working on that. I'm sure I'll look at some in the future. I'll definitely cover the VIC-20 more in the future, so stay tuned 😃
Fantastic video Noel. The VIC-20 was my first computer. Unfortunately I don't have it anymore, but I can emulate it on my Retropie. Your knowledge is always inspiring. Keep up the good work.
What you have seen in the S-Video mod looks like Chroma Shift. Luma and Chroma are in a time offset. As we are talking about milliseconds, this delay could be induced by the analogue circuit (the charging curve of the capacitor). And in the end, you always need to consider the 75 ohms termination to avoid signal reflectoin and shadows. But so far so good, great mod
Hi Noel, nice explain for the Vic-20 mod. I did something similar, but i've placed a extra i.c. socket on the existing socket and bended out pin 2 to connect the cap and resistor on it. That way you just can pull it out again to revert to the original situation. Also my chroma and luminance were separated that way. All that is connected to a S-video connector.
Ouch! Well, then that means almost for sure your VIC chip is busted. I wonder why they tend to fail in multicolor mode. I've seen a couple in online forums with the same problem.
Likely the capture card is missing the 75 ohm (?) termination resistor. I know I removed one from my capture stick when I was trying to intercept some video stream and it came out too dark.
I'm not an analogue electronics expert by any means, but it looks to me that the capacitor you added between the colour signal and the composite output is applying a small amount of positive feedback to the output transistor. Since the transistor is largely configured as an emitter follower and therefore can't really have a gain greater than 1 the feedback is probably acting more like a schmitt trigger, squaring up the signal somewhat . The result looks to me like its removing the dark "shadow" after pixels, which makes the picture look better. If this works under all circumstances I cannot say, but the example pictures you show seem to be a huge improvement. If the board gets hot after a lot of use that might affect the characteristics of the transistor and make the circuit oscillate, but if that is true only time will tell! Great video again, and thought provoking as usual.
Interesting. I hadn't thought about it that way, but that makes sense in a very handwavy kind of way 😃 I know this was not a mod I was able to explain, but I'm glad I put it out there some people can chime in with their thoughts and share their expertise (which I don't have in this particular kind of circuits). Hopefully I can learn enough from that to explain it and improve it in the future. Cheers!
If you want more options for using composite and s-video on modern displays and capture devices, I highly recommend the retrotink 2x mini, which is a low latency line doubler with HDMI output. It's my go-to for checking s-video mods, since my 15k crt only supports rf and composite.
Good point. I've read about the RetroTink, but I don't own one. OSSC usually does it for me for video capture, but that doesn't support S-video like the Retro Tink.
Since all/most of the companies are long gone, I made a lot of them myself from high-resolution logos and sometimes I had to make the logos myself 😃 www.latostadora.com/retrocomputers/
When I did the Nintendo Color TV Game 15 to Component mod, I got a really washed out picture and I just experimented with small capacitors until the trace on the oscilloscope looked really nice. When I hooked it back up to the monitor, the picture was super sharp.
Can't say about your s-video to scart adapter but scart can work in s-video mode when croma is hooked to red pin and luma to composite. Suppose some voltages has to be apllied on some control pins to signal to the TV that S-video is used. So if adapter is made correctly and it is not mixing signals to make composite it should provide better picture.
Right. From my research your TV also needs to support it, and not old TVs do it correctly since S-video was added after the SCART standard. So I'm still unsure if mine supports it or not 😃
The 0.01u capacitor in series with the 220p could be replaced with a short. The combination is essentially 220p. Removing the ferrite bead is probably what helped here.
Really nice videomod! I have a PAL VIC-20 with a CR board too and I want to try this mod. My video looks just as your "before" images except it doesn't have the broken multicolor mode thankfully. Will be very interesting to see if there's going to be a as notable difference on my board too. Thanks for this video and guide Noel! EDIT: Btw if a game shows up in a square in the corner like that, you can move it to the center using the cursor keys :)
Thank you! Glad you liked it. Please let me know how it goes if you make the mod. And good tip about the arrows. Someone told me about it after I made the video, but I still haven't tried it. Is it a standard thing, or did every game have to implement that separately, do you know?
@@NoelsRetroLab I've placed an order for the capacitors needed so I will recieve them some time next week. Will try to remember to post my results here. Pretty sure the thing with the games and the cursor keys is standard, it worked for many of the games I have on my Penultimate + cartridge at least. Think I heard about it from a video by The 8 Bit Guy.
@@NoelsRetroLab I finally got the components to perform the mod on my VIC 20. It was very easy and my board was surprisingly clean so it was a dream to work on. My board was revision D Assy no 250403 from 1982 and it also had a resistor going diagonally over the brightness potentiometer. I replaced it with a 220 pF capacitor in the way you showed in the video. The results of the mod was nothing short of amazing! The picture quality is fantastic! I can't believe a composite signal can look this clean. Both high res games and multi color games looks super crisp. Thank you so much for finding this out and sharing with us! I'm blown away comparing my before and after direct captures :D
Thanks for the the good content and God bless ya. Commodore VIC 20's are pretty nonexistant in South Africa and there is very few C64's floating around. It's because of trade embargoes that computers in general were very expensive in the 80's and early 90's.
Glad you enjoyed it! What were the most popular personal computers in South Africa in the 80s? If Commodores are out I imagine Ataris were out as well. Was it MSX? Sinclair? Apples?
Bit late on the info, but when it comes to S-Video over SCART, it's an odd cludge, the signals actually are kept separate (so long as the adaptor is wired to do so), the Luminance goes into the Composite input pin, and the Chrominance is fed via the Red input of the RGB side of things, and set to the right input mode, the TV then knows what to do with the signals to process them into an image... :) I learned this the other day when I thought my 64c had conked out, as all I was seeing on my TV was a red image, and, I forgot I had to hit the Input selection button on the front of the TV (Sony KV-14M1U, slightly older model than yours I think) to switch it to S-Video, oops!!! :P
you can have 100 VICs and get 100 different results... 15:14 - normaly these adaptors are wired to the Scart direct and without combining them again. The TV then uses both signals (if capable to do so!). Sure that your adaptor does combine them?
Do you think it would possible to use a daughter board in the VIC slot with the VIC chip on that so that a custom video output circuit could be used to experiment with instead of it using the native video output?
Yes, definitely! That's what I was kind of hinting about. I would probably start with the composite circuit from the C64 on a daughterboard and go from there.
@@NoelsRetroLab Your hinting obviously worked! VIC20 was my first computer and many happy hours was spent playing Radar Rat Race and Blitz on it so I wish you the best of luck and can’t wait to see more videos about it :)
I can't speak for your TV or your adapter, but s-video over scart does not combine it back to composite. Luma is put in the port for composite and chroma is transmitted over the pin usually used for red in an RGB cable. Of course the TV needs to know, that there is s-video incoming. The osd of May preferred crt lets my choose between composite and s-video for AV2, which is not RGB capable. Wegen connecting s-video and choosing composite, it's only displaying the luma aus black and white
Hi Noel, I have a very early NTSC Vic-20 with the 2-prong power connector. I would like to perform this mod on it, do you have written instructions or a guide that I could follow?
Para saber si ese adaptador a euroconector combina las señales de S-Video en video compuesto: -Si el adaptador NO combina las señales, habrá continuidad entre el pin 4 (croma) del mini-DIN y el pin 15 del euroconector y entre el pin 3 (luma) y el 20. -Si el adaptador SÍ combina las señales, sólo habrá continuidad entre el pin 3 del mini-DIN y el pin 20 del euroconector, y deberías poder medir un condensador entre los pines 3 y 4 del mini-DIN. Creo recordar que a finales de los 80 se amplió la especificación del euroconector para dar soporte a S-Video. Si ese adaptador no combina las señales, yo probaría a meter una señal de S-Video para ver si alguna de las pantallas lo soportan. La que no lo soporte te dará una bonita imagen en blanco y negro.
i think you would really need a high quality scope, maybe even with an active probe to not alter the signal with the probe and then check chroma and luma separately without the circuitry and tinker around with the right transistor amplifier. maybe on a separate board to have more freedom in design. for that you could carve out the circuit for luma first to get a crystal clear black and white signal first. with the chroma it might be more difficult to not mess up the phase. also the luma should not contain frequencies that could interfere with chroma. i guess that is really something for a tv technician who is familiar with these things. in your latest mod, it looked like chroma is coming late and the lcd monitor puts the chroma to the next pixel. is there a way to make an "all-pass" filter for luma that just delays luma? btw. does the retro tink make use of a real s-video signal?
I used probes in the x10 mode, so I think that's good enough not to modify the video signals much at all (after all, they look the same on the screen while I'm measuring them). It's also pretty handy for crystal oscillator signals. I agree about having a separate board for testing things. That'd be ideal. One thing I didn't show was removing the chrome signal completely, and the image was super sharp. So I think the luminance one is all good and it's a matter of synchronizing the other one and removing bad frequencies like you said 👍
Well done! I'd must know.... how do you capture your scope? I was just given a brand new Yeapook 100mhz digital scope and would like to know how you manage to capture your screen. Again... awesome retro goodness!
@@darkstatehk I know it can hook up to a USB port but the manual is not very thorough. It's a Yeapook ASD1013D. Someone was kind enough to give it to me.
Thanks! I capture it the lowest tech way imaginable: I have an articulated arm on my workbench where I can put my phone and I point it straight at the scope and I record from there 😃 Then, in Premiere, since both the main camera and the phone recorded the same sound, I can synchronize the tracks automatically and that's it (usually with some perspective correction to get the scope more square to the camera).
Hi, Thanks for this great video. I tried this mod but unfortunately the result is worst than before. The ghosting is yellow (previously white) and more visible. My VIC-20 is a PAL version but I’m don’t know how to see if it’s a CR. I Also made a change: i didn’t have a 470nF ceramic so I replaced it with a 0.47uF electrolytic, will it make a difference ? Best regards
Great video, I love the VIC-20! The Dig Dug version is really good, but unfortunately on the PAL VIC-20 it's running way too fast and is therefore not much fun to play. Noel, maybe you could think about a fix? :D
Oh right! Being a rushed NTSC port, everything is probably 15-20% faster in the PAL version. Haha! I'm sure there's an easy patch that can be done to the game. I'm not the right person to do it, but check around in the Denial forum.
1:50 You picked a good VIC to work on. I don't have one that's as bad as this one 7:00 This kind of breakdown is exactly why I love vintage machines. You really can understand every component. In large part because you have access to it. Can't pin out a modern graphics system quite this easily ;-) 8:30 Excellent visual 9:00 Also really excellent is Programming the VIC by Raeto Collin West. There is a version of this book by the same author for the 64 which is probably the book you should own if you can only have one book. 19:20 Yeah, I wish there was a neat and clean answer for this too. As you know I've done this same mod with similar results but I wish I understood better why it works. 22:40 Very happy to see the VIC-20 getting some love. It's my third favorite computer of all time. Excellent work Noel.
It funny you say that because the people in the Denial forum said that this VIC-20 looks really good. Better than the majority! Haha! It may have to do with the fact that mine had a diagonal capacitor instead of a resistor like most seem to do. Completely agreed about retro machines being awesome precisely because you can fully "grok" them!
I'm really curious on why composite causes that horrible checkered pattern noise on modern LCD. Specially on high contrast text. Pal N64 is famous to be a really ugly case for it. S-video improves it, but I wonder if a simple (generic or not) circuit would improve it.
I wish I'd known about this when I was 9 :-) I used to hate the red pixel characters. They always looked like "rope" to me as a kid. I did the S-Video mod on one of my PAL Vics a few years ago. It was definitely the sharpest I've ever seen a Vic image (my TV and monitor both have S-Video) but I had some serious ghosting. Now my Vic chip is dead (and I ain't going to pay for another) I'm waiting for the day when I feel like implementing an FPGA VGA solution.. unless someone beats me to it.
People are already working on VIC replacements, so that's promising. I'm assuming you need an NTSC one, because the PAL VIC chips are still pretty reasonable (around 10€).
@@NoelsRetroLab I need a PAL one.. but the cost of a chip and postage to NZ is ridiculous. I have no patience with CRTs these days so I'd reall like a VGA mod anyway :-) I kinda like the idea of having a go at modding one myself. I started learning about FPGAs but then I've become distracted trying to make my own computer as is often the case.
Great stuff Noel, I'm curious to know if the partially working VIC's still exhibit the same issues after the composite mod? I assume they do, as you say it seems to be a problem internal to the IC but maybe worth another look? 13:10 I think that may also be a 220pf cap in the other VIC20, just in a package similar to a resistor
Thanks! Yes, I did put the original VIC chip back in and it had a similarly-improved image. And good catch about the diagonal component being a capacitor. It crossed my mind at some point but then I forgot about it. I should go back and check because a resistor doesn't seem to make much sense there.
What about using a Raspberry Pi to sample the Red,Blue and Green and output a HDMI signal but there must be some way to add sound to the signal except for rewriting the application to accommodate the sound as well.
I believe the RGB to HDMI project has a mode that accepts YUV. It can probably be extended (if it's not already) to deal with luminance/chroma. But in this case personally I don't want HDMI, but good ol' composite to use my CRT TV 😃
Not sure to be honest. I haven't started my VIC-20 repair series yet, so I don't have a good suggestion. My initial thought is that maybe it's ROM related? Like it's setting up the right colors but then it hangs somehow? Try putting a cartridge and see if that works.
Hello, why not recover the Chroma signal (chrominance) from FB7 (removal of the component) and repatriate this chroma signal to a 5-pin female DIN connector fixed on a new small inverted PCB over the location of the old DIN (on the motherboard) ?? The best solution is to not modify anything on the VIC-20 motherboard. Simply “clean” the original Composite signal using a CLEAR VIDEO device (PCB) attached to the video chip socket. Once the Composite signal is correctly "cleaned" of all its parasites, the video display quality will also be better than the S-Video hardware mod which consists of DESTROYING the motherboard with a screwdriver or cutter.😜😉 Congratulations on your very informative work.👍
Great video as usual Noel. I'd ask that you cut the chiptune music whilst talking though. When you were showing the oscilloscope readings it was really distracting.
Thanks for the feedback. I've been experimenting with the editing, so I'll try to reduce that or lower the volume. It definitely should not be distracting 👍
Duda, donde consigues tantos ordenadores para reparar? Yo he buscado por webs como Ebay o Wallapop, pero esque ahí la gente pone unos precios desorbitados por un aparato estropeado.
@@renepedersen7141 I switched mine on on each step of the mod, and in one of them, the output was worse than before. Only after the adding of the 470pF to pin 5 with the wire on the underside made the signal better. So maybe at this last step, something didn't work out?
Noel! Coming from anyone else this would be a good-to-great video. But you're better than solutions-by-accident! Your circuit, from a circuit-theoretical point of view, cannot be optimal (it actually doesn't make much sense, as you're mixing the same signals twice, before and after buffering, applying different frequency filters each time; this is certain to be reducible). It may just happen to work given the impedance characteristics and frequency response of the particular display you're using, or the particular frequency response of the amplifying transistor Q2 on your board, which may have deteriorated over time for certain bands of the spectrum (and therefore things improve if you bypass Q2). You could try a faster (and new) amplifying transistor there. With an S-video mod, Q2 deals with a fairly narrow band, so it isn't critical. But since you're sticking to composite, Q2 needs to have a clean frequency response so the information in the color subcarrier can be interpreted correctly. I'd change Q2 and see what happens.
Haha, thanks! I'm afraid my experience relies 100% in the digital realm, and when you get me out into the analog world, I don't have the experience/knowledge to really understand the nuances of a circuit. I did reach out to a couple of people and they seemed to think that having a high-frequency path to the end wasn't a horrible thing, but that's as far as I got. But anyway, I'm planning to revisit this video issue with any new insights, and maybe also trying to mimic the C64 composite video signal circuit (since that one looks fantastic). I'll ping you for some ideas when I do that if you don't mind.
@@MichaelDoornbos A high-frequency one, with collector-to-emitter current over 100mA. Would have to look at a transistor table to make a specific choice.
So you converted C13 into a 219pf capacitor by adding the 0.1uf in series with it. I suspect if you replaced C13 with a trimmer cap you would have better results. I like your video's, but you kind of got lucky on this one.
Oh no doubt that was just dumb luck. I wanted to share that and get opinions from people who really grok those kind of circuits and maybe we can make sense out of it and improve it. I like the idea of using a trimmer a lot. I don't have any on hand, but that's a great idea. Cheers.
I'm the guy who developed the S-video mod as described in the Denial wiki. While I never made any attempts to improve the composite output, I can give some explanations and suggestions you might find of value. Firstly, the red trimmer adjusts the colour subcarrier frequency, if it is incorrectly adjusted, you may get 'Hannover Bars' in coloured areas. You can see an example of those in the bottom two images in the Denial S-video wiki page. If the adjustment is off by too much, the colour may completely drop out. This applies to PAL. NTSC does not have the 180 deg alternate phase reversal, so if this trimmer is out of adjustment, the colours will all be wrong.
The key to maximum video quality is correct video levels. Firstly, your TV/monitor should be presenting a 75 ohm load to the input video signal. The video should be 1 volt, measured between the bottom of the sync pulse and the white level. This is adjusted with the trimpot as you describe in the video. Additionally, with the entire video signal at 1 volt, you should have 0.3 volts between the bottom of the sync pulse and black level. This relationship is fixed within the VIC chip.
The colour level should be at 0.3 volts peak-to-peak on the colour burst signal. There is no means to adjust this in an unmodified VIC-20 and it is normally way too high. This is why you get the serrated edges between different coloured areas. It is actually called 'Dot Crawl'. Normally on a proper interlaced video signal, these dots will slowly crawl up or down, but on a VIC-20 they are stationary. You will never be able to eliminate dot crawl, however it can be reduced by two methods.
The first method is to reduce the colour level to at least the correct 0.3 volts. You could reduce the colour level further, which will further reduce dot crawl, but you will eventually get to a point where the colour will get noisy or blurry or even become prone to dropping out.
The second method (and which is possibly what is happening in your modification) is to restrict the low frequency bandwith of the colour signal (before it is combined with the luminance signal). This will have the side effect of smearing the colours somewhat, and may even cause some smearing of the luminance signal too.
Your LCD monitor would most likely have a comb filter in it which is a far more sophisticated method of separating the chrominance from the luminance. This almost entirely eliminates dot crawl as you have observed. Your CRT monitor would use the old bandpass filter method which is far less effective.
Finally, I have noticed there is an amazing variation in picture quality between different VIC chips. Often these are temperature sensitive. I have one VIC chip that gives an OK image when cold, but after a while the blue parts of the image go all noisy, blurry and are full of 'jailbars' once the chip warms up.
Excellent information. Thanks! When I revisit this VIC-20 (which I'll have to because it gives you weird diagnostic errors), I'll have another look at the signal with your information. Thanks!
Hello @a4000bear Thank you for your very useful comment which reinforces the choice I recently made with my Vic20, namely that it is the type of monitor which above all allows for optimal image quality.
Soon I'm going to pick up a Panasonic Plasma TV (TH-42PV500) screen (used for €70).
I will first plug the Vic20's S-VIDEO SCART cable directly into the Panasonic Plasma TV to see the result.
Then, I will use a converter (active/5v USB-C power supply) by connecting the S-VIDEO SCART socket of the Vic20 to the SCART input of the converter and at the output of the converter the RCA / RGB socket to the Panasonic TV screen in Plasma.
My converter allows adjustment of RGB colors using three potentiometers if necessary.
According to my analysis, I will not need to modify the hardware part as was done in this video by @NoelsRetroLab
PS: I have two VIC20s for this test, a British Vic20 and a German VC20 (very rare Vic20 model)
D00d! Correlating the O Scope with the screen capture, AND showing the probe points on the schematic. Winning! This is some of the most effective signal level description of a computer system I've seen. Excellent, and thank you!
Thank you! I'm really glad you liked that. I really try to show what I'm doing so people can really grasp it and do it themselves if they want to.
With the aging of all of the important MOS chips, I'll be interested in the VIC chip replacement projects going on
Yes! I've been starting to follow one of those projects and it looks very interesting.
For someone who knows as much as I do (nothing) this video was extremely educational, thank you.
Thanks,I thought it was just my old tv set.Now watching your vic20 stuff before attempting my repairs.These are the most useful of all the offerings on youtube on this subject so far.
That was really great! The VIC 20 doesn’t get enough love from the retro community. I’m currently trying to recreate my original setup at the moment - just the expansion slot extender, joystick and one game to go before I have exactly what I had as a kid (except it’s NTSC instead of PAL).
Very nice! It's a really fun little system that gets overshadowed by the C64.
I've just done this to my Vicky Twenty and I'm blown away by the result. It took a bit of figuring out because that board doesn't have the 'original' position of C13 marked, so I just had to figure out where to solder that cap. The rest of the mod was just the same. It's perfect for me. I had been planning to make the s-video mod but didn't like the idea of having a dangling s-video cable, or fitting an s-video socket. This is perfect, I just use the original video socket as before. Thank you so much!
That's great to hear! Glad it worked for you too.
i miss my vic-20! i read the programming guide back to front when i was a kid to get a handle on what it could do.
Such a great book!! 😃
Thankyou so much. I have just had this modification done to my Vic20 and the graphics and text are SO SO much better. Thanks for sharing.
With most cartridges, it is possible to position the „active area“ of the screen output with the cursor keys. So, the monitor being in the upper left corner is not a thing, you have to live with.
Right! Slowly learning my way around the VIC-20 😃
Fantastic work, the VIC-20 doesn't get enough love. It's the first computer I ever experienced, I was maybe only 3 or 4 years old at the time.
It's a really, really fun computer. You'll definitely be seeing more of it here 😃
I have a SCART adapter just like you shown at 15:22 and I sacrificed its plastic case in the name of science. And I was surprised to find out that chroma and luma signals from the S-video connector go to 2 different pins on the SCART connector. Whether or not your TV would to make anything out of it, of course, depends entirely on the TV.
I am guessing that there are at least the two versions, one that creates a composite signal and one that keeps chrominance and luminance apart. Why not simply try a beeping multimeter for signal continuity and the SCART pinout... en.wikipedia.org/wiki/SCART
That was a lovely explanation. I might want to do experiments on my dear Viccy.
Hi Noel, I've just performed the same surgery on my newly acquired VIC-20 (PAL version), but I'm getting a yellow shadow on the left hand side of the letters. Same power up display as yours at 20:55 The display is far better than it was though, so is certainly a vast improvement.
Edit: I've improved it even more. After some experimentation, I went back to the beginning and removed the 470N cap and just replaced the ferrite bead (or 100n cap) with a 2K resistor. I've introduced an RC network in effect. 2K ohms value was chosen using a test 10K potentiometer. All yellow shadows have completely gone now. I'm really pleased I found your video. Many thanks.
The answer is the ferrite bead is a small value inductor and it causes ringing. You remove and you get rid of the ringing.
The usual way to get rid of that ringing is to put a low value damping resistor in parallel with it, you'll often find that done with a coil wound onto a resistor in CRT gun drivers, if you remove the resistor or it goes open circuit then you get ringing and smearing on screen.
@@M0UAW_IO83 AFAIK, this dampening resistor will reduce the impedance of the load on the VIC-I's output and this could damage it.
That makes sense. That's what I had read too. Any idea why they put it there in the first place? The C64 and VIC-20 are full of those ferrite beads everywhere!
@@NoelsRetroLab Engineers at the time assumed this would reduce the noise just like it often does with digital signals. If you look at the design on C64 boards, those of 1982/1983 also have ferrite beads. They disappeared on boards 250425 (1984) and afterwards.
Except ferrite beads are generally lossy. They appear resistive at high frequencies. It shouldn't cause ringing like a true inductor would. (However, it sure looks like it is from looking at the output on screen.)
Hello, Thank you for your very useful comment which reinforces the choice I recently made with my Vic20, namely that it is the type of monitor which above all allows for optimal image quality.
Soon I'm going to pick up a Panasonic Plasma TV (TH-42PV500) screen (used for €70).
I will first plug the Vic20's S-VIDEO SCART cable directly into the Panasonic Plasma TV to see the result.
Then, I will use a converter (active/5v USB-C power supply) by connecting the S-VIDEO SCART socket of the Vic20 to the SCART input of the converter and at the output of the converter the RCA / RGB socket to the Panasonic TV screen in Plasma.
My converter allows adjustment of RGB colors using three potentiometers if necessary.
According to my analysis, I will not need to modify the hardware part as was done in this video.
PS: I have two VIC20s for this test, a British Vic20 and a German VC20 (very rare Vic20 model)
I just did your mod, Noel, and it's freaking awesome! Luckily, the multi color mode also still works on my machine. Yay! Thanks so much!
Thanks Noel! That's fantastic...I've managed to do it! And now I have kind of a "HiRes" Vic20. No fear of destroying my nostalgic memory: I prefer to feel my Vic20 still "alive" and so evolving :-) Your video had been a milestone for my 'relationship' with it! :-) Much appreciated!
Another very nice video from Noel. Every video I watch, a new idea I get to repair something I have on my list. Keep up the good work !!!
Thanks 👍
Awesome video as usual Noel. I agree with other comments that the VIC-20 doesn't nearly as much attention as it deserves. This video has made me check the hires mode on my own VIC-20, a very early one with PET style keys, and I'm happy to report that the video output looks exactly like your one with the properly working VIC chip does - phew!
Yay! Good thing because I don't think there are easy replacements for the VIC chip yet, although some projects are working on that. I'm sure I'll look at some in the future. I'll definitely cover the VIC-20 more in the future, so stay tuned 😃
Fantastic video Noel. The VIC-20 was my first computer. Unfortunately I don't have it anymore, but I can emulate it on my Retropie. Your knowledge is always inspiring. Keep up the good work.
Thank you!
What you have seen in the S-Video mod looks like Chroma Shift. Luma and Chroma are in a time offset. As we are talking about milliseconds, this delay could be induced by the analogue circuit (the charging curve of the capacitor). And in the end, you always need to consider the 75 ohms termination to avoid signal reflectoin and shadows. But so far so good, great mod
it is about a time offset in the area of 200-500 nanoseconds
Hi Noel, nice explain for the Vic-20 mod. I did something similar, but i've placed a extra i.c. socket on the existing socket and bended out pin 2 to connect the cap and resistor on it. That way you just can pull it out again to revert to the original situation. Also my chroma and luminance were separated that way. All that is connected to a S-video connector.
Nice. No cutting tracks that way. Do you have a cable running out the back or did you manage to reuse the video connector somehow?
@@NoelsRetroLab Yes, there is a extra cable comming out.
Found memories of the Vic-20 as it was my first home computer! Excellent work Noel!
Perhaps time that I revisited the sad looking Vic20 in the attic. Gorf used to look great, now it looks like before you started your repair!
Ouch! Well, then that means almost for sure your VIC chip is busted. I wonder why they tend to fail in multicolor mode. I've seen a couple in online forums with the same problem.
Noel you are a wizard.
Likely the capture card is missing the 75 ohm (?) termination resistor. I know I removed one from my capture stick when I was trying to intercept some video stream and it came out too dark.
I'm not an analogue electronics expert by any means, but it looks to me that the capacitor you added between the colour signal and the composite output is applying a small amount of positive feedback to the output transistor. Since the transistor is largely configured as an emitter follower and therefore can't really have a gain greater than 1 the feedback is probably acting more like a schmitt trigger, squaring up the signal somewhat . The result looks to me like its removing the dark "shadow" after pixels, which makes the picture look better. If this works under all circumstances I cannot say, but the example pictures you show seem to be a huge improvement. If the board gets hot after a lot of use that might affect the characteristics of the transistor and make the circuit oscillate, but if that is true only time will tell! Great video again, and thought provoking as usual.
Interesting. I hadn't thought about it that way, but that makes sense in a very handwavy kind of way 😃 I know this was not a mod I was able to explain, but I'm glad I put it out there some people can chime in with their thoughts and share their expertise (which I don't have in this particular kind of circuits). Hopefully I can learn enough from that to explain it and improve it in the future. Cheers!
Awesome stuff Noel! obviously... as usual :D
Nice video and nice introduction of the VIC20 internals!
Hope to see more VIC20 soon! :-)
Greetings, Doc64!
Thank you very much!
If you want more options for using composite and s-video on modern displays and capture devices, I highly recommend the retrotink 2x mini, which is a low latency line doubler with HDMI output. It's my go-to for checking s-video mods, since my 15k crt only supports rf and composite.
Good point. I've read about the RetroTink, but I don't own one. OSSC usually does it for me for video capture, but that doesn't support S-video like the Retro Tink.
Best retro channel on UA-cam :)
Btw, where do you get your sweet looking T-shirts?
Since all/most of the companies are long gone, I made a lot of them myself from high-resolution logos and sometimes I had to make the logos myself 😃 www.latostadora.com/retrocomputers/
When I did the Nintendo Color TV Game 15 to Component mod, I got a really washed out picture and I just experimented with small capacitors until the trace on the oscilloscope looked really nice. When I hooked it back up to the monitor, the picture was super sharp.
Right. Sometimes you do stuff like that and then reason it backwards. Or try to anyway 😃 That's all part of the scientific approach.
Really enjoyed this, even though I never had a VIC-20.
Can't say about your s-video to scart adapter but scart can work in s-video mode when croma is hooked to red pin and luma to composite. Suppose some voltages has to be apllied on some control pins to signal to the TV that S-video is used. So if adapter is made correctly and it is not mixing signals to make composite it should provide better picture.
Right. From my research your TV also needs to support it, and not old TVs do it correctly since S-video was added after the SCART standard. So I'm still unsure if mine supports it or not 😃
@@NoelsRetroLab newer TV's probably should.
The 0.01u capacitor in series with the 220p could be replaced with a short. The combination is essentially 220p. Removing the ferrite bead is probably what helped here.
2:30 - We've had a problem. Check for an under-volt on bus B
Really nice videomod! I have a PAL VIC-20 with a CR board too and I want to try this mod. My video looks just as your "before" images except it doesn't have the broken multicolor mode thankfully. Will be very interesting to see if there's going to be a as notable difference on my board too. Thanks for this video and guide Noel!
EDIT: Btw if a game shows up in a square in the corner like that, you can move it to the center using the cursor keys :)
Thank you! Glad you liked it. Please let me know how it goes if you make the mod.
And good tip about the arrows. Someone told me about it after I made the video, but I still haven't tried it. Is it a standard thing, or did every game have to implement that separately, do you know?
@@NoelsRetroLab I've placed an order for the capacitors needed so I will recieve them some time next week. Will try to remember to post my results here. Pretty sure the thing with the games and the cursor keys is standard, it worked for many of the games I have on my Penultimate + cartridge at least. Think I heard about it from a video by The 8 Bit Guy.
@@NoelsRetroLab I finally got the components to perform the mod on my VIC 20. It was very easy and my board was surprisingly clean so it was a dream to work on. My board was revision D Assy no 250403 from 1982 and it also had a resistor going diagonally over the brightness potentiometer. I replaced it with a 220 pF capacitor in the way you showed in the video. The results of the mod was nothing short of amazing! The picture quality is fantastic! I can't believe a composite signal can look this clean. Both high res games and multi color games looks super crisp. Thank you so much for finding this out and sharing with us! I'm blown away comparing my before and after direct captures :D
Vic-20 was my first computer. Used it with a black and white portable TV - looks odd to me seeing it in color.
Very nice work, as always.
2 non-functional VIC 20’s? Can we expect a VIC 20 repairathon in the future? That would be really cool!
Oh yes! I actually have 4 non-functional ones 😱 So yes, I've already made a VIC-20 playlist and everything in preparation.
Fucking entropy killing integrated circuits
Thanks for the the good content and God bless ya. Commodore VIC 20's are pretty nonexistant in South Africa and there is very few C64's floating around. It's because of trade embargoes that computers in general were very expensive in the 80's and early 90's.
Glad you enjoyed it! What were the most popular personal computers in South Africa in the 80s? If Commodores are out I imagine Ataris were out as well. Was it MSX? Sinclair? Apples?
Bit late on the info, but when it comes to S-Video over SCART, it's an odd cludge, the signals actually are kept separate (so long as the adaptor is wired to do so), the Luminance goes into the Composite input pin, and the Chrominance is fed via the Red input of the RGB side of things, and set to the right input mode, the TV then knows what to do with the signals to process them into an image... :)
I learned this the other day when I thought my 64c had conked out, as all I was seeing on my TV was a red image, and, I forgot I had to hit the Input selection button on the front of the TV (Sony KV-14M1U, slightly older model than yours I think) to switch it to S-Video, oops!!! :P
poke 646,10 is the same as poke 646,2 and is the same as CTRL+3. Not sure why you mentioned that it changes the graphics mode.
you can have 100 VICs and get 100 different results...
15:14 - normaly these adaptors are wired to the Scart direct and without combining them again. The TV then uses both signals (if capable to do so!). Sure that your adaptor does combine them?
Very nice video. Thanks!
Do you think it would possible to use a daughter board in the VIC slot with the VIC chip on that so that a custom video output circuit could be used to experiment with instead of it using the native video output?
Yes, definitely! That's what I was kind of hinting about. I would probably start with the composite circuit from the C64 on a daughterboard and go from there.
@@NoelsRetroLab Your hinting obviously worked! VIC20 was my first computer and many happy hours was spent playing Radar Rat Race and Blitz on it so I wish you the best of luck and can’t wait to see more videos about it :)
As usual a great video!
Glad you enjoyed it!
I can't speak for your TV or your adapter, but s-video over scart does not combine it back to composite. Luma is put in the port for composite and chroma is transmitted over the pin usually used for red in an RGB cable. Of course the TV needs to know, that there is s-video incoming. The osd of May preferred crt lets my choose between composite and s-video for AV2, which is not RGB capable. Wegen connecting s-video and choosing composite, it's only displaying the luma aus black and white
i see you found a working "74LC" :P
great stuff Noel... that image looks 100x better!
Oh, that was not for this. That's for a C64 repair. I'm usually working on videos that are released 3-4 weeks later 😃
@@NoelsRetroLab SMH!... i remember you saying C64 now! ...was thinking something was off when i seen comments from 5 days ago!
@@NoelsRetroLab, it was for the C64 board that was built from scratch and didn't work, did I guess correctly?
Hi Noel, I have a very early NTSC Vic-20 with the 2-prong power connector. I would like to perform this mod on it, do you have written instructions or a guide that I could follow?
Para saber si ese adaptador a euroconector combina las señales de S-Video en video compuesto:
-Si el adaptador NO combina las señales, habrá continuidad entre el pin 4 (croma) del mini-DIN y el pin 15 del euroconector y entre el pin 3 (luma) y el 20.
-Si el adaptador SÍ combina las señales, sólo habrá continuidad entre el pin 3 del mini-DIN y el pin 20 del euroconector, y deberías poder medir un condensador entre los pines 3 y 4 del mini-DIN.
Creo recordar que a finales de los 80 se amplió la especificación del euroconector para dar soporte a S-Video. Si ese adaptador no combina las señales, yo probaría a meter una señal de S-Video para ver si alguna de las pantallas lo soportan. La que no lo soporte te dará una bonita imagen en blanco y negro.
i think you would really need a high quality scope, maybe even with an active probe to not alter the signal with the probe and then check chroma and luma separately without the circuitry and tinker around with the right transistor amplifier.
maybe on a separate board to have more freedom in design. for that you could carve out the circuit for luma first to get a crystal clear black and white signal first. with the chroma it might be more difficult to not mess up the phase. also the luma should not contain frequencies that could interfere with chroma. i guess that is really something for a tv technician who is familiar with these things.
in your latest mod, it looked like chroma is coming late and the lcd monitor puts the chroma to the next pixel. is there a way to make an "all-pass" filter for luma that just delays luma?
btw. does the retro tink make use of a real s-video signal?
I used probes in the x10 mode, so I think that's good enough not to modify the video signals much at all (after all, they look the same on the screen while I'm measuring them). It's also pretty handy for crystal oscillator signals.
I agree about having a separate board for testing things. That'd be ideal. One thing I didn't show was removing the chrome signal completely, and the image was super sharp. So I think the luminance one is all good and it's a matter of synchronizing the other one and removing bad frequencies like you said 👍
Well done! I'd must know.... how do you capture your scope? I was just given a brand new Yeapook 100mhz digital scope and would like to know how you manage to capture your screen. Again... awesome retro goodness!
Can u plug your scope to your computer network? If yes open web browser and type in the scope IP address. You can see the trace from there.
@@darkstatehk I know it can hook up to a USB port but the manual is not very thorough. It's a Yeapook ASD1013D. Someone was kind enough to give it to me.
Thanks! I capture it the lowest tech way imaginable: I have an articulated arm on my workbench where I can put my phone and I point it straight at the scope and I record from there 😃 Then, in Premiere, since both the main camera and the phone recorded the same sound, I can synchronize the tracks automatically and that's it (usually with some perspective correction to get the scope more square to the camera).
@@NoelsRetroLab Ah... Ok..... I thought you had some cool kind of feature on your scope but I suppose that works as well. Nice!
Looking forward to the rest of the video but I had to pause to come here and ask, did you say “1 megaHert”?
More from the '20 please, it's got such great arcade games!
Coming up! 😃
Hi, Thanks for this great video. I tried this mod but unfortunately the result is worst than before. The ghosting is yellow (previously white) and more visible. My VIC-20 is a PAL version but I’m don’t know how to see if it’s a CR. I
Also made a change: i didn’t have a 470nF ceramic so I replaced it with a 0.47uF electrolytic, will it make a difference ?
Best regards
See my post above regarding the yellow ghosting cure.
Great video, I love the VIC-20! The Dig Dug version is really good, but unfortunately on the PAL VIC-20 it's running way too fast and is therefore not much fun to play. Noel, maybe you could think about a fix? :D
Oh right! Being a rushed NTSC port, everything is probably 15-20% faster in the PAL version. Haha! I'm sure there's an easy patch that can be done to the game. I'm not the right person to do it, but check around in the Denial forum.
I am sure you are supposed to us a non-metal screwdriver when adjusting the pots on a powered board.
i remeber it was also a big price tag on vic 64 and vic 20 my mom went NOOOOOOOOOOOOOOOO thank you for upload every interesting .)
1:50 You picked a good VIC to work on. I don't have one that's as bad as this one
7:00 This kind of breakdown is exactly why I love vintage machines. You really can understand every component. In large part because you have access to it. Can't pin out a modern graphics system quite this easily ;-)
8:30 Excellent visual
9:00 Also really excellent is Programming the VIC by Raeto Collin West. There is a version of this book by the same author for the 64 which is probably the book you should own if you can only have one book.
19:20 Yeah, I wish there was a neat and clean answer for this too. As you know I've done this same mod with similar results but I wish I understood better why it works.
22:40 Very happy to see the VIC-20 getting some love. It's my third favorite computer of all time.
Excellent work Noel.
It funny you say that because the people in the Denial forum said that this VIC-20 looks really good. Better than the majority! Haha! It may have to do with the fact that mine had a diagonal capacitor instead of a resistor like most seem to do.
Completely agreed about retro machines being awesome precisely because you can fully "grok" them!
I'm really curious on why composite causes that horrible checkered pattern noise on modern LCD. Specially on high contrast text.
Pal N64 is famous to be a really ugly case for it. S-video improves it, but I wonder if a simple (generic or not) circuit would improve it.
I wish I'd known about this when I was 9 :-) I used to hate the red pixel characters. They always looked like "rope" to me as a kid. I did the S-Video mod on one of my PAL Vics a few years ago. It was definitely the sharpest I've ever seen a Vic image (my TV and monitor both have S-Video) but I had some serious ghosting. Now my Vic chip is dead (and I ain't going to pay for another) I'm waiting for the day when I feel like implementing an FPGA VGA solution.. unless someone beats me to it.
People are already working on VIC replacements, so that's promising.
I'm assuming you need an NTSC one, because the PAL VIC chips are still pretty reasonable (around 10€).
@@NoelsRetroLab I need a PAL one.. but the cost of a chip and postage to NZ is ridiculous. I have no patience with CRTs these days so I'd reall like a VGA mod anyway :-) I kinda like the idea of having a go at modding one myself. I started learning about FPGAs but then I've become distracted trying to make my own computer as is often the case.
Great stuff Noel, I'm curious to know if the partially working VIC's still exhibit the same issues after the composite mod? I assume they do, as you say it seems to be a problem internal to the IC but maybe worth another look?
13:10 I think that may also be a 220pf cap in the other VIC20, just in a package similar to a resistor
Thanks! Yes, I did put the original VIC chip back in and it had a similarly-improved image.
And good catch about the diagonal component being a capacitor. It crossed my mind at some point but then I forgot about it. I should go back and check because a resistor doesn't seem to make much sense there.
What about using a Raspberry Pi to sample the Red,Blue and Green and output a HDMI signal but there must be some way to add sound to the signal except for rewriting the application to accommodate the sound as well.
I believe the RGB to HDMI project has a mode that accepts YUV. It can probably be extended (if it's not already) to deal with luminance/chroma. But in this case personally I don't want HDMI, but good ol' composite to use my CRT TV 😃
If your going to do that, You may as well just emulate the VIC 20 on a Raspberry PI and put it in the VIC 20 case. :)
@@frankowalker4662 #Copperdragon has already do so so it is tile Noel got a few of these replacements.
Hi Noel i have a vic 20 with only a blue cyan screen on boot what it can be??im looking everywhere to find some ways to revive this VIc20 :)
Not sure to be honest. I haven't started my VIC-20 repair series yet, so I don't have a good suggestion. My initial thought is that maybe it's ROM related? Like it's setting up the right colors but then it hangs somehow? Try putting a cartridge and see if that works.
@@NoelsRetroLab No when i start the vic 20 i got a signal from composite cable and the screen is all cyan blue im gonna try it ! thanks :)
I have an NTSC VIC-20. I want to check this mod with it.
Great. Let me know how it goes! (or drop by the Discord server and show us pics even 😃).
Hello, why not recover the Chroma signal (chrominance) from FB7 (removal of the component) and repatriate this chroma signal to a 5-pin female DIN connector fixed on a new small inverted PCB over the location of the old DIN (on the motherboard) ??
The best solution is to not modify anything on the VIC-20 motherboard. Simply “clean” the original Composite signal using a CLEAR VIDEO device (PCB) attached to the video chip socket.
Once the Composite signal is correctly "cleaned" of all its parasites, the video display quality will also be better than the S-Video hardware mod which consists of DESTROYING the motherboard with a screwdriver or cutter.😜😉
Congratulations on your very informative work.👍
Great video as usual Noel. I'd ask that you cut the chiptune music whilst talking though. When you were showing the oscilloscope readings it was really distracting.
Thanks for the feedback. I've been experimenting with the editing, so I'll try to reduce that or lower the volume. It definitely should not be distracting 👍
Duda, donde consigues tantos ordenadores para reparar? Yo he buscado por webs como Ebay o Wallapop, pero esque ahí la gente pone unos precios desorbitados por un aparato estropeado.
Por Wallapop sobre todo, pero hace años. Últimamente la cosa sea ha puesto como dices. Creo que hace más de un año que no compro nada por ahí.
Where can I get the Colour Test V1 program please?
Good question indeed!
I tried this hack on my VIC20, it had the opposite effect. Maybe it works well on some machines :) VIC chips are different.
Interesting! So far everybody had good results with it. Thanks for letting me know! Was it a PAL CR model? Were you using an LCD or a CRT display?
@@NoelsRetroLab PAL CR machine and LCD display. Maybe it's just my lack of luck :) I made s-video hack on another VIC20 last year, works perfect :)
@@renepedersen7141 I switched mine on on each step of the mod, and in one of them, the output was worse than before. Only after the adding of the 470pF to pin 5 with the wire on the underside made the signal better. So maybe at this last step, something didn't work out?
wow gorf......that took me back lol
Noel! Coming from anyone else this would be a good-to-great video. But you're better than solutions-by-accident! Your circuit, from a circuit-theoretical point of view, cannot be optimal (it actually doesn't make much sense, as you're mixing the same signals twice, before and after buffering, applying different frequency filters each time; this is certain to be reducible). It may just happen to work given the impedance characteristics and frequency response of the particular display you're using, or the particular frequency response of the amplifying transistor Q2 on your board, which may have deteriorated over time for certain bands of the spectrum (and therefore things improve if you bypass Q2). You could try a faster (and new) amplifying transistor there. With an S-video mod, Q2 deals with a fairly narrow band, so it isn't critical. But since you're sticking to composite, Q2 needs to have a clean frequency response so the information in the color subcarrier can be interpreted correctly. I'd change Q2 and see what happens.
Haha, thanks! I'm afraid my experience relies 100% in the digital realm, and when you get me out into the analog world, I don't have the experience/knowledge to really understand the nuances of a circuit. I did reach out to a couple of people and they seemed to think that having a high-frequency path to the end wasn't a horrible thing, but that's as far as I got. But anyway, I'm planning to revisit this video issue with any new insights, and maybe also trying to mimic the C64 composite video signal circuit (since that one looks fantastic). I'll ping you for some ideas when I do that if you don't mind.
What transistor would you try at Q2?
@@NoelsRetroLab Sure thing!
@@MichaelDoornbos A high-frequency one, with collector-to-emitter current over 100mA. Would have to look at a transistor table to make a specific choice.
best thing are the tshirts almost.. haha
So you converted C13 into a 219pf capacitor by adding the 0.1uf in series with it. I suspect if you replaced C13 with a trimmer cap you would have better results. I like your video's, but you kind of got lucky on this one.
Oh no doubt that was just dumb luck. I wanted to share that and get opinions from people who really grok those kind of circuits and maybe we can make sense out of it and improve it. I like the idea of using a trimmer a lot. I don't have any on hand, but that's a great idea. Cheers.
⭐⭐⭐⭐⭐
DOOD!
just get a clearvideo for the vic-20
Elon Musk has a VIC-20 as a kid and look at him now.
That was back when he was cool 🤣
now he is cheating with acceleration times.