That audio circuit looks badly designed, but I believe the polarised capacitors are correct. Am I missing something?... (All sheet 2...) U204 is powered from just under 12v-0-12v (via R207, R208, R209 and R210) yet the input is biased to +2.5v via R200, R209 and R210 which generate the "Vref" signal (fed to 10 and 12). Since the input is biased positive as above, the outputs of the U204 bandpass filters (Pins 1 and 7) are likely to be positive when no audio is playing as it's a DC chain. That would make the capacitor design in the shown circuit correct. The capacitors should be fine as they were since the signal output connectors should always be lower in voltage on "No audio" and will very likely stay that way when audio is playing as the audio is very unlikely to be more than a 2v deviation each way. Can someone measure the voltage at pin 1 or 7 when there's no audio playing? I expect just below +2.5v, due to Vref biasing. Checking using a scope, with loud audio playing too would be interesting. I don't expect the pins 1 or 7 will go below 0v. This DC output design seems to only be fixed in the A4000_Rb and A4000CR_Rd diagram by adding another opamp to the chain. All other models were the "+DC design" as above. ---------------------------- As an extra thing I think I spotted. I don't know about the Paula outputs on 30 and 31, but they appear to be getting forced to Vref via R230 and R240. That seems a bad idea, even though the feedback is through a 360ohm resistor. Just seems wrong. Shouldn't there be capacitor coupling on the outputs of 30 and 31? Not had an Amiga in 25 years so can't test this myself! :-)
Thanks for pointing that out! I was kind of wondering why the audio output worked so well with the "wrong" type of capacitors still. Never came to my mind to measure the bias voltage. I'm definitely going to do a little follow up video and debunk that myth and looking at the output on a scope. :D
"As an extra thing I think I spotted. I don't know about the Paula outputs on 30 and 31, but they appear to be getting forced to Vref via R230 and R240" The outputs from Paula are current outputs, not voltage outputs. This is quite common for a lot of DACs. The opamps are being used as an I/V converter stage in this case, where R230/240 set the gain. The +ve input of those opamps is biased to Vref as this the "virtual ground" point around which the audio signal is biased - because Paula only has a single 5V supply.
Great video Jan =D Always interesting to see faults like that - where it's not your typical failure etc and takes a bit of tracing to find the issue. I've got a similar video going up today (where it's not obvious what the cause is) - I've given you a shoutout at the end of it just now as I filmed the final part. Great work, loving the Amiga videos!
I found your channel through this video and was just watching your intro. I had a similar issue and was about to lose my pilots license because of it. My Dr said there's nothing I can do because of my age etc, but then I came across a book by Dr Barry and dug deeper. It's a long story but I was able to correct things without surgery, it just took a lot of work doing exercises and a patch. So if it's amblyopia chances are you can do the same.
Thanks Chris! I kind of took the long route to find the fault but really enjoyed the process. Looking forward to watching your video later today. Thanks for the shout in advance. ;)
Nice video, kinda glad that im not the only one messing upp stuff 😂 Every time I see your clean shiny A2000 i start to wrestle my mind between taking mine apart to clean or just finish the damn build
The audio output caps actually don't need to be bipolar. Even though the opamp has dual supplies, the audio signal actually has a constant positive DC offset on it - hence the capacitors. As long as the capacitors are in there the right way (+ve end toward the opamp), everything is fine :)
Exactly.. Drives me nuts whenever I hear this complaint about using electrolytics here.. The first op-amps are referenced to Vref ~2.5v, and the output never swings negative.. The second op-amp is just a follower, so also stays positive too.. The capacitors are here to remove this DC offset, and it's always in that direction.. arrgghh.. There's a video on youtube somewhere where one of the Amiga designers points out that this wasn't an error.
@@donvito1973 they were fitted the wrong way around on some Amiga boards, ie the -ve was towards the opamp, which damaged the capacitor - but thats all.
Why didn't you start at testing continuity between R208 and power connector, and voltage drop across R208? This 10 Ohm resistor is the only thing between PSU -12V line and the op-amp. The diodes you tested are not in this circuit, they are for -12V_USER, not for -12V used in U204. C223 (47 uF) is effectively in parallel to this cap near the power connector, that's why your ESR meter has shown ~100uF.
Yeah, I took the long route I guess. Also mistook another resistor for R208 so that had me confused a bit. Probably should have started tracing right after checking the PSU voltage though. Still learning...
Hi Jan, Just wanted to share my experiences about the coupling electrolytics there. I've seen some brand-name audio amplifiers with polarized electrolytics in the signal path which were a couple of decades old and those capacitors were still perfectly good (in spec and still providing good sound). However, I've tried to use non-polarized electrolytics in the signal path and I was lead by the same logic as you and I've made the sound only worse. On the other hand, the non-polar electrolytics can be found in speaker crossover networks and they are there for a reason though. The voltages there are much higher and a polarized cap would fail shortly. If you still want to use the non-polarized caps in audio path, I suggest metal film caps (MKP or similar). I bet that if you put a 4.7uF MKP cap there (1uF - 10uF is OK I think), the sound output would be great, provided that you don't connect those outputs to a low input impedance (less than 1kOhm) audio device. Cheers!
Some commenters pointed out that in this case the polarized caps are actually correct because the output is biased to 2.5V. Makes perfect sense. I know that some hifi stuff uses bipolar caps so I didn't even think of measuring the output myself. Maybe I'll still experiment with MKP caps for fun and see if that makes a difference in sound quality. Thanks for sharing your thoughts on this!
Thanks for the video Jan. You fixed it, but more importantly what skills did you learn while doing it? Below are some of my thoughts on this; it is not criticism, just some advice from someone who has been fixing things for over 30 years and is a big Commodore fan. --- In the video, I noticed that you had a tendency to start blaming components right away. Instead, think of it a bit like solving a crime; you need to gather evidence first :) Troubleshooting is like any other trade; it takes practice to get good at it. You are already better now than when you started doing this. Perhaps think about the steps involved in solving for "root cause", in your case it was no -12V to the op-amp. Measure power circuit resistance from the source to the destination and from ground to the destination. Right away you will know if the power circuit is broken or if it is shorted to ground... evidence is gathering! For broken circuits, cut the problem in half by finding a component in-circuit (hopefully literally 1/2 way to the destination) and measure resistances to power and ground. You have then cut the size of the problem in half. Do it over again to quickly narrow down the suspects, find the guilty party and convict them with the strong evidence you have gathered. OK its a bit of a cheesy analogy but it does help me to give advice on how to think about performing root-cause analysis. And your meter is a really good instrument, use it more to help you, primarily voltages and resistances then only later on start measuring capacitors to prove your case. One point on going back to a previous repair as you did here. When starting, think about the areas that you touched before and add them to the suspect list. Everyone makes mistakes and it may have been a previous repair which cased the fault (as it looks to be in this case). Thanks for putting these video up, been watching for years now and its great to see C-64's and Amiga getting restored and put back in use! Cheers,
Thanks for the tips Eddy! Very much appreciated, I'm learning new stuff all the time and comments like yours are very helpful. Troubleshooting was a bit random but fun on this one, I admit. ;)
Great fault finding there Jan, this always happens with this older kit. Funnily enough Turrican / TFMX tunes would be the best test for this also as it used time splitting on the 4 chans to give a virtual 7 ergo the great intro tune there. Great video as always
Great diagnostics troubleshooting! What solder are you using? What wattage soldering iron are you using? Great video. Warning (Suggestion). Using a Electrostatic wrist strap with only chassis ground connection is not recommended. While large static charges are affected by chassis grounding, smaller charges will not be properly grounded out. When working on or near ESD sensitive components true grounding is necessary. I always use a purpose built ground cord. Take a typical power extension cord and physical disconnect all power connections from the power outlet side of the extension cable. LEAVE ONLY THE GROUND CONNECTION ATTACHED TO THE EXTENSION CABLE ON THE POWER CORD. Mark the extension cord with green electrical tape or green heat shrink on both ends of the power extension cable. Replace the alligator clip on the ESD wrist strap with a standard power cord plug (use the end which plugs into the typical wall power outlet). Now all you have to do is make sure the power outlets you have are actually physically connected to earth ground. Good luck, I keep my ESD wrist strap near the door to my workbench room. The ESD wrist strap is the first tool I use everyday. BTW, remove all magnetic items from the room (like the magnetic parts bowl you are using) you are working with ICs in. This is especially important with CPU ICs or memory ICs. If you find that your metal tools are becoming magnetized, either remove them from your workroom or de-magnitize the tools. Tool suggestion: buy a set of "Fluke AC280 SureGrip Hook Clips". If you are regularly checking power or continuity measurements, these hook-clips will save time and reduce false readings from poor connections.
I've got a BBC Master - condition unknown - that I'm itching to have a crack at. I'm hoping for not working but an easy fix. That way I'll feel like I did something good.
Fascinating trouble shooting with a happy ending. It seemed more complex to start with but ended up being a simple fix, how often does that happen :-) I learned something. Cheers.
Great video! Could you please make a video of your usage of tools e.g. grounding of you (blue wire on your wrist) , how is it connected (mains ground?) How do you use the voltage meter measures of connectivity, voltage, ESR with and without voltage on the board? How to use the oscilloscope (mains ground) with power supplies on the breadboard? Tools you clean boards with brushes etc. Again thanks for great content
5 Zorro II slots , 1 Video Slot, CPU Slot, 4 ISA slots (we could have done without them) plus all the usual ports, what's not to like. It was one of the most flexible systems ever made.
Correction! Thanks Peter! You are right, the audio signal is biased by Vref. So you need the cap to filter the DC offset! --- Previous comment: By the way... at a dual supply op Amp audio amplifier you don't even need a cap on the output. Greetings, Doc64! ---
Not true - it depends on how the opamp is configured. In this case the first stage I/V conversion is biased around a voltage reference, so there is always a +ve DC offset
Hi Peter! Yes, you are absolutely right. Now, after Jans "Bipolar Capacitors in the Amiga Audio Circuit?" video I took some more time to investigate the OpAmp audio circuit and then have seen that the non inverting input is connected to Vref not to GND. So thanks for your correction. Greetings, Doc64!
I got an Amiga 500 recently and it had a similar audio issue but sound was almost entirely broken. For most parts it didn't even play and when it did it was distorted. Turned out that -12V line on power supply was dead so I replaced the power regulator and now it's good as new.
I usually use Panasonic FC series caps I order from different electronics retailers. You can also get kits, for example from amigastore: amigastore.eu/en/475-capacitor-pack-for-a2000.html
If you have no voltage on U204 rails it has to be either and open circuit resistor R207 or R208 depending on which rail is missing or an open circuit track. Removing the IC was a waste of time because if it was pulling the supply down the resistor in that rail would cook dissipating approx 10W.
Awesome find there Jan, glad you god that sound pumping :-) My daughter and I are presently in the workshop playing your end credits over and over again hahahahahah this is the second time I've had to clean up coffee from my desk, last time was Chris in bed with that A2000 LOL!!!!!
Das mit der Spannung ist der Standartfehler aber auch beim 500er kann es so sein. Und die Turrican II Diskette ist der schnellste Weg einem einem Amiga einen Top Sound zu entlocken. Hatte ich beim basteln damals stundenlang laufen lassen. Disk rein 20 Sekunden warten ==> Musik.
Ja, ist ein klassischer Fehler auch beim 500er. Manchmal hat auch einfach ein Pin am Netzteilstecker keinen guten Kontakt und führt dann zu verzerrtem Sound. Chris Hülsbeck hat mit den Turrican Soundtracks wirklich kleine Meisterwerke geschaffen. :)
Has anybody tried to get Linux to run on Amiga? Especially if you can adapt an SSD to work with its onboard cache and memory would help. Where is the Dac ic, is it the Philips tda1541
There’s no dedicated DAC, audio is generated by the Paula chip (that also has a lot of other functions) and then amplified by the little circuit shown in the video.
I remember having Debian on my 1200 around the mid nineties. The only "problem" was you need a CPU with an MMU, so the cheap "EC" variety68k chips would not work. A decent 030 accelerator does the job just fine.
Mein Amiga 1200 macht beim Sound auch Probleme..denk mal jetzt sind die Kondensatoren wirklich hin...und der Fbas Ausgang hält das Signal auch nicht..es flackert und Bild wird hell und dunkel..mein 1200 ist Baujahr 1995 😳
Wenn du den noch nicht Recapped hast, ist das wirklich höchste Zeit. Die SMD Kondensatoren in den Amigas aus der Ära sind so gut wie alle leck (zumindest soweit ich die gesehen habe). Das kann dann tatsächlich zu allen möglichen Fehlern führen, im schlimmsten Fall ätzt dir das austretende Elektrolyt die Leiterbahnen kaputt. :/
Ist es schlimm zu sagen, dass mir die verzerrte Musik gefallen hat?, Really though that's a fault I can't say I've ever come across myself. At least it was a simple fix like makin' a better solder connection, that is usually the case when there isn't a bad trace anyway I suppose. There is always a chance that somethin' will go wrong with solderin' from the factory it can't always be perfect.
It's kind of the metal version of the Turrican theme I guess... ;) Yeah, there's always the risk of damaged joints and traces escpecially on a PCB this large. In this case, I think it was me who scraped some of the trace away during recapping.
That audio circuit looks badly designed, but I believe the polarised capacitors are correct. Am I missing something?...
(All sheet 2...)
U204 is powered from just under 12v-0-12v (via R207, R208, R209 and R210) yet the input is biased to +2.5v via R200, R209 and R210 which generate the "Vref" signal (fed to 10 and 12).
Since the input is biased positive as above, the outputs of the U204 bandpass filters (Pins 1 and 7) are likely to be positive when no audio is playing as it's a DC chain.
That would make the capacitor design in the shown circuit correct. The capacitors should be fine as they were since the signal output connectors should always be lower in voltage on "No audio" and will very likely stay that way when audio is playing as the audio is very unlikely to be more than a 2v deviation each way.
Can someone measure the voltage at pin 1 or 7 when there's no audio playing? I expect just below +2.5v, due to Vref biasing.
Checking using a scope, with loud audio playing too would be interesting. I don't expect the pins 1 or 7 will go below 0v.
This DC output design seems to only be fixed in the A4000_Rb and A4000CR_Rd diagram by adding another opamp to the chain. All other models were the "+DC design" as above.
----------------------------
As an extra thing I think I spotted. I don't know about the Paula outputs on 30 and 31, but they appear to be getting forced to Vref via R230 and R240. That seems a bad idea, even though the feedback is through a 360ohm resistor. Just seems wrong. Shouldn't there be capacitor coupling on the outputs of 30 and 31?
Not had an Amiga in 25 years so can't test this myself! :-)
Thanks for pointing that out! I was kind of wondering why the audio output worked so well with the "wrong" type of capacitors still. Never came to my mind to measure the bias voltage. I'm definitely going to do a little follow up video and debunk that myth and looking at the output on a scope. :D
"As an extra thing I think I spotted. I don't know about the Paula outputs on 30 and 31, but they appear to be getting forced to Vref via R230 and R240"
The outputs from Paula are current outputs, not voltage outputs. This is quite common for a lot of DACs.
The opamps are being used as an I/V converter stage in this case, where R230/240 set the gain. The +ve input of those opamps is biased to Vref as this the "virtual ground" point around which the audio signal is biased - because Paula only has a single 5V supply.
Look up "Transimpedance amplifier" on Wikipedia and that will show you how Paula's audio output stage works :)
@@jaycee1980 So that makes sense for the Paula. Thanks.
Great video Jan =D Always interesting to see faults like that - where it's not your typical failure etc and takes a bit of tracing to find the issue. I've got a similar video going up today (where it's not obvious what the cause is) - I've given you a shoutout at the end of it just now as I filmed the final part. Great work, loving the Amiga videos!
I found your channel through this video and was just watching your intro. I had a similar issue and was about to lose my pilots license because of it. My Dr said there's nothing I can do because of my age etc, but then I came across a book by Dr Barry and dug deeper. It's a long story but I was able to correct things without surgery, it just took a lot of work doing exercises and a patch. So if it's amblyopia chances are you can do the same.
Thanks Chris! I kind of took the long route to find the fault but really enjoyed the process. Looking forward to watching your video later today. Thanks for the shout in advance. ;)
Look forward to the video fella...
Great effort humming along to Turrican in the closing credits Jan. I lost it. LOL
Haha, glad you liked it. :)
That's the down side to re-capping something like this you can generate other faults but at least you managed to find it and sort it out, well done.
it would have broken eventually if not recapped...
Thanks, yes, there's always a risk to it of course. But in the long run, I think it's necessary.
Good video. The music in these old games is awesome
It is! The Turrican music remains to be one of my favorites. :)
You need to do your best Perifractic impression on the PCB way ad. He does a very good Jan Beta impression, you should return the compliment.
Haha, maybe I will. ;)
Great video Jan 👍🏻 from Denmark 😁
The mighty Amiga sounds great again
Thanks! :)
The 7V you were seeing on the opamp -V pin would have been the opamp's internal biasing... because the -V supply pin was open
That makes sense!
Wuhuuu! Isn't that always a great feeling if a problem can be fixed! Greetings, Doc64!
It certainly is!
Nice video, kinda glad that im not the only one messing upp stuff 😂
Every time I see your clean shiny A2000 i start to wrestle my mind between taking mine apart to clean or just finish the damn build
Haha, the board looks shiny on mine but the case is really messy. There’s going to be a lot of work getting that looking shiny again. :)
My case looks super! Together we have on 100% shiny machine
@@DomedagsPoeten You should both send it to me and I will test it all for you! :-)
Good find Jan. I thought I saw some brown scratches near where you were soldering the repair but that was probably just superficial.
The audio output caps actually don't need to be bipolar. Even though the opamp has dual supplies, the audio signal actually has a constant positive DC offset on it - hence the capacitors. As long as the capacitors are in there the right way (+ve end toward the opamp), everything is fine :)
Exactly.. Drives me nuts whenever I hear this complaint about using electrolytics here.. The first op-amps are referenced to Vref ~2.5v, and the output never swings negative.. The second op-amp is just a follower, so also stays positive too.. The capacitors are here to remove this DC offset, and it's always in that direction.. arrgghh.. There's a video on youtube somewhere where one of the Amiga designers points out that this wasn't an error.
@@donvito1973 they were fitted the wrong way around on some Amiga boards, ie the -ve was towards the opamp, which damaged the capacitor - but thats all.
Good point, I'd still like to check with an oscilloscope across the cap or something. Theory is nice but seeing is believing :)
@@benbaselet2026 retrogamemodz did that on one of his videos while troubleshooting an audio issue in an A1200
Ha! I'll have to do a follow up video debunking that myth sometime soon. Thanks!
I would never have caught that! Nice job, Jan!
Thanks Doug! :D
Why didn't you start at testing continuity between R208 and power connector, and voltage drop across R208? This 10 Ohm resistor is the only thing between PSU -12V line and the op-amp. The diodes you tested are not in this circuit, they are for -12V_USER, not for -12V used in U204. C223 (47 uF) is effectively in parallel to this cap near the power connector, that's why your ESR meter has shown ~100uF.
Yeah, I took the long route I guess. Also mistook another resistor for R208 so that had me confused a bit. Probably should have started tracing right after checking the PSU voltage though. Still learning...
Hi Jan,
Just wanted to share my experiences about the coupling electrolytics there. I've seen some brand-name audio amplifiers with polarized electrolytics in the signal path which were a couple of decades old and those capacitors were still perfectly good (in spec and still providing good sound). However, I've tried to use non-polarized electrolytics in the signal path and I was lead by the same logic as you and I've made the sound only worse. On the other hand, the non-polar electrolytics can be found in speaker crossover networks and they are there for a reason though. The voltages there are much higher and a polarized cap would fail shortly. If you still want to use the non-polarized caps in audio path, I suggest metal film caps (MKP or similar). I bet that if you put a 4.7uF MKP cap there (1uF - 10uF is OK I think), the sound output would be great, provided that you don't connect those outputs to a low input impedance (less than 1kOhm) audio device.
Cheers!
Some commenters pointed out that in this case the polarized caps are actually correct because the output is biased to 2.5V. Makes perfect sense. I know that some hifi stuff uses bipolar caps so I didn't even think of measuring the output myself.
Maybe I'll still experiment with MKP caps for fun and see if that makes a difference in sound quality. Thanks for sharing your thoughts on this!
Enjoy these videos. Glad you were able to fix it.
Thanks Steven! :D
Thanks for the video Jan. You fixed it, but more importantly what skills did you learn while doing it?
Below are some of my thoughts on this; it is not criticism, just some advice from someone who has been fixing things for over 30 years and is a big Commodore fan.
---
In the video, I noticed that you had a tendency to start blaming components right away. Instead, think of it a bit like solving a crime; you need to gather evidence first :)
Troubleshooting is like any other trade; it takes practice to get good at it. You are already better now than when you started doing this.
Perhaps think about the steps involved in solving for "root cause", in your case it was no -12V to the op-amp. Measure power circuit resistance from the source to the destination and from ground to the destination. Right away you will know if the power circuit is broken or if it is shorted to ground... evidence is gathering!
For broken circuits, cut the problem in half by finding a component in-circuit (hopefully literally 1/2 way to the destination) and measure resistances to power and ground. You have then cut the size of the problem in half. Do it over again to quickly narrow down the suspects, find the guilty party and convict them with the strong evidence you have gathered.
OK its a bit of a cheesy analogy but it does help me to give advice on how to think about performing root-cause analysis. And your meter is a really good instrument, use it more to help you, primarily voltages and resistances then only later on start measuring capacitors to prove your case.
One point on going back to a previous repair as you did here. When starting, think about the areas that you touched before and add them to the suspect list. Everyone makes mistakes and it may have been a previous repair which cased the fault (as it looks to be in this case).
Thanks for putting these video up, been watching for years now and its great to see C-64's and Amiga getting restored and put back in use!
Cheers,
Thanks for the tips Eddy! Very much appreciated, I'm learning new stuff all the time and comments like yours are very helpful. Troubleshooting was a bit random but fun on this one, I admit. ;)
Great fault finding there Jan, this always happens with this older kit. Funnily enough Turrican / TFMX tunes would be the best test for this also as it used time splitting on the 4 chans to give a virtual 7 ergo the great intro tune there.
Great video as always
Thanks Nigel! Didn't think of the virtual channels although I heard about it. Right choice in every respect then. ;)
Really enjoyed the video Jan, love how you fault find. Another project completed ☺
Thanks! The A2000 project is still ongoing for a while though. ;)
Great diagnostics troubleshooting! What solder are you using? What wattage soldering iron are you using? Great video.
Warning (Suggestion). Using a Electrostatic wrist strap with only chassis ground connection is not recommended. While large static charges are affected by chassis grounding, smaller charges will not be properly grounded out. When working on or near ESD sensitive components true grounding is necessary. I always use a purpose built ground cord. Take a typical power extension cord and physical disconnect all power connections from the power outlet side of the extension cable. LEAVE ONLY THE GROUND CONNECTION ATTACHED TO THE EXTENSION CABLE ON THE POWER CORD. Mark the extension cord with green electrical tape or green heat shrink on both ends of the power extension cable. Replace the alligator clip on the ESD wrist strap with a standard power cord plug (use the end which plugs into the typical wall power outlet). Now all you have to do is make sure the power outlets you have are actually physically connected to earth ground. Good luck, I keep my ESD wrist strap near the door to my workbench room. The ESD wrist strap is the first tool I use everyday.
BTW, remove all magnetic items from the room (like the magnetic parts bowl you are using) you are working with ICs in. This is especially important with CPU ICs or memory ICs. If you find that your metal tools are becoming magnetized, either remove them from your workroom or de-magnitize the tools.
Tool suggestion: buy a set of "Fluke AC280 SureGrip Hook Clips". If you are regularly checking power or continuity measurements, these hook-clips will save time and reduce false readings from poor connections.
Interesting video :) I recently got a vic20 I thought was broken. I was disappointing when it worked :P
Haha, I know that feeling. Troubleshooting can be a lot of fun, at least if you can get stuff working in the end. ;)
I've got a BBC Master - condition unknown - that I'm itching to have a crack at. I'm hoping for not working but an easy fix. That way I'll feel like I did something good.
@@philrod1 At the school I worked at the BBC Master was the Econet and hard drive server.
Fascinating trouble shooting with a happy ending. It seemed more complex to start with but ended up being a simple fix, how often does that happen :-) I learned something. Cheers.
Thanks Pauline! A bit aimless at first but in the end I found the broken trace. ;)
Great video!
Could you please make a video of your usage of tools e.g. grounding of you (blue wire on your wrist) , how is it connected (mains ground?)
How do you use the voltage meter measures of connectivity, voltage, ESR with and without voltage on the board?
How to use the oscilloscope (mains ground) with power supplies on the breadboard?
Tools you clean boards with brushes etc.
Again thanks for great content
Nice Job! The A2000 is still my absolute favorite Amiga!
5 Zorro II slots
, 1 Video Slot, CPU Slot, 4 ISA slots (we could have done without them) plus all the usual ports, what's not to like. It was one of the most flexible systems ever made.
It's a wonderful machine indeed. :)
Correction! Thanks Peter! You are right, the audio signal is biased by Vref. So you need the cap to filter the DC offset!
--- Previous comment: By the way... at a dual supply op Amp audio amplifier you don't even need a cap on the output. Greetings, Doc64! ---
Not true - it depends on how the opamp is configured. In this case the first stage I/V conversion is biased around a voltage reference, so there is always a +ve DC offset
Hi Peter! Yes, you are absolutely right. Now, after Jans "Bipolar Capacitors in the Amiga Audio Circuit?" video I took some more time to investigate the OpAmp audio circuit and then have seen that the non inverting input is connected to Vref not to GND. So thanks for your correction. Greetings, Doc64!
Top work Jan!
Thank you! :D
Awesome work. Very informative
I got an Amiga 500 recently and it had a similar audio issue but sound was almost entirely broken. For most parts it didn't even play and when it did it was distorted.
Turned out that -12V line on power supply was dead so I replaced the power regulator and now it's good as new.
Yes, from what I've read that's the most common fault for audio issues. Nice work on fixing that regulator! :)
Another great vid Jan and great fix... Salute..
Thanks Paul! :)
hi, where can i find excellent capacitors for amiga 2000 rev4.4 thanks
I usually use Panasonic FC series caps I order from different electronics retailers. You can also get kits, for example from amigastore: amigastore.eu/en/475-capacitor-pack-for-a2000.html
When working with large circuit boards like this, any flexing in the board can break traces like that.
Yes, might have happened just like that. My desk is a bit too small for the large PCB, too.
Excellent work. I admire your skill.
Thanks! :)
Nice quick repair.. Thanks for the video.
Glad you liked it! :D
Good repair! Nice work!
Thanks Tommy! :D
very simple problem just very difficult to find good job :)
Yes, admittedly my troubleshooting was a bit random at first, too. But luckily I succeeded in the end. ;)
I literally hit the imaginary toms right when you did lmfao good stuff
Good job. That is one big motherboard!
It is! My desk is a bit too small to work on it properly really. :)
If you have no voltage on U204 rails it has to be either and open circuit resistor R207 or R208 depending on which rail is missing or an open circuit track.
Removing the IC was a waste of time because if it was pulling the supply down the resistor in that rail would cook dissipating approx 10W.
Nice repair Jan 🤗🤗 Kim 😁😁
Thank you Kim! :D
Awesome find there Jan, glad you god that sound pumping :-) My daughter and I are presently in the workshop playing your end credits over and over again hahahahahah this is the second time I've had to clean up coffee from my desk, last time was Chris in bed with that A2000 LOL!!!!!
Haha, nice! Glad you enjoyed the little joke. ;)
Nice repair and interesting problem! Thanks
Glad you found it interesting. :D
Awesome fix on video as always 👍🏻❤️
Thanks Joseph! :D
Das mit der Spannung ist der Standartfehler aber auch beim 500er kann es so sein.
Und die Turrican II Diskette ist der schnellste Weg einem einem Amiga einen Top Sound zu entlocken.
Hatte ich beim basteln damals stundenlang laufen lassen.
Disk rein 20 Sekunden warten ==> Musik.
Ja, ist ein klassischer Fehler auch beim 500er. Manchmal hat auch einfach ein Pin am Netzteilstecker keinen guten Kontakt und führt dann zu verzerrtem Sound. Chris Hülsbeck hat mit den Turrican Soundtracks wirklich kleine Meisterwerke geschaffen. :)
Well done !
Thanks! :)
UGH. there was some horrible distortion @24:47 you need to fix that now! ;-)
Ha!
Has anybody tried to get Linux to run on Amiga? Especially if you can adapt an SSD to work with its onboard cache and memory would help. Where is the Dac ic, is it the Philips tda1541
That’s something that Druaga1 would do!
Linux was ported to the Amiga back in 1993.
Have a look at www.debian.org/ports/m68k/
I guess nowadays it's more common the other way round ;)
There’s no dedicated DAC, audio is generated by the Paula chip (that also has a lot of other functions) and then amplified by the little circuit shown in the video.
I’d love to see Druaga1 do that. :D
I remember having Debian on my 1200 around the mid nineties. The only "problem" was you need a CPU with an MMU, so the cheap "EC" variety68k chips would not work. A decent 030 accelerator does the job just fine.
Great fix!
Thanks Andrew! :)
Saubere Arbeit!
Vielen Dank! :)
Awesome video, I loved it.
Thanks Martin!
Awwh yeah! That Turrican music.
BUEN TRABAJO!!!
Thank you! :)
Mein Amiga 1200 macht beim Sound auch Probleme..denk mal jetzt sind die Kondensatoren wirklich hin...und der Fbas Ausgang hält das Signal auch nicht..es flackert und Bild wird hell und dunkel..mein 1200 ist Baujahr 1995 😳
Wenn du den noch nicht Recapped hast, ist das wirklich höchste Zeit. Die SMD Kondensatoren in den Amigas aus der Ära sind so gut wie alle leck (zumindest soweit ich die gesehen habe). Das kann dann tatsächlich zu allen möglichen Fehlern führen, im schlimmsten Fall ätzt dir das austretende Elektrolyt die Leiterbahnen kaputt. :/
Great video, but the sound level on the video was so low it made me think something was wrong with my sound card!
Thanks! Yes, the sound level turned out to be even lower than in my other videos. I'm going to work on that, thanks for pointing it out. :)
Ist es schlimm zu sagen, dass mir die verzerrte Musik gefallen hat?, Really though that's a fault I can't say I've ever come across myself. At least it was a simple fix like makin' a better solder connection, that is usually the case when there isn't a bad trace anyway I suppose. There is always a chance that somethin' will go wrong with solderin' from the factory it can't always be perfect.
It's kind of the metal version of the Turrican theme I guess... ;) Yeah, there's always the risk of damaged joints and traces escpecially on a PCB this large. In this case, I think it was me who scraped some of the trace away during recapping.
Es geht doch nichts über eine Prise Chris Hülsbeck am Morgen :-)