ZX Spectrum 128K "Toastrack" Mega Repair (Part 1)
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- Опубліковано 10 чер 2024
- Support Noel's Retro Lab on Patreon: / noelsretrolab
This board of a Sinclair ZX Spectrum 128K "Toastrack" stopped working when an expansion was plugged in on the edge connector while it was powered on. Initially I thought this was going to be a quick repair with a blown transistor (I even say it's a "Nibble edition" in the intro 🤣🤣), but as I kept going deeper and deeper, more things were coming up as faulty. How many things were blown up? Will it come back to life or is it gone?
Chapters:
00:00 Intro
01:34 Initial power up
02:58 Video out test
03:16 Measuring voltages
04:02 Testing transistors
09:54 Replacing TR4
12:25 Testing the Z80
16:36 Examining the busses
19:49 Testing the ULA
22:32 Testing the ZX8401
23:43 Testing the RAM
26:09 Final body count
Links:
ZX Dandanator Mini www.dandare.es/Proyectos_Danda...
ZX Diagnostics github.com/brendanalford/zx-d...
Connect with Noel's Retro Lab:
Discord ➤ / discord
Facebook ➤ / noelsretrolab
Twitter ➤ / noelsretrolab
Instagram ➤ / noelsretrolab
#zxspectrum #repair #sinclair - Наука та технологія
![ПОЛНАЯ ИСТОРИЯ ЭКЗОРЦИЗМА [Топ Сикрет]](http://i.ytimg.com/vi/qBySr6Bt0B8/mqdefault.jpg)
Your NPN / PNP transistor explanation was the best I’ve seen. Also am impressed by the schematic graphic with the indicator which shows what pin you are probing on the ICs. This makes your channel unique. Well done. You’ve got a new subscriber. PS: this is the first time I have ever commented on a UA-cam video so your work was that impressive. Cudos.
Wow! Thank you so much! Glad you enjoyed it.
Your channel really deserves more subscribers. There are so many "retro" channels now but most of them are "I cleaned the keyboard in the dishwasher and retrobrighted the case" instead of actually knowing what they are doing.
Thanks! Those can also be quite interesting sometimes. There's room for a lot of different approaches because different people get different things out them. I'm sure I'm scaring a lot of people away every time I put the oscilloscope on the screen :-)
Noel's Retro Lab The oscilloscope shots make it easier to follow what’s going on. I like the more technical reasoning that goes beyond “this chip feels hot, so it must be dead” or random chip swapping until it works.
I also like that you’re repairing Spectrums, and not C64s 😀
@@ncot_tech Thanks! Although I like to get into and repair all sorts of computers, C64s included :-) But I agree, some European computers don't get much love on UA-cam.
Oh my god man, I just got a non working ZX Toastrack and couldn’t get a picture, a search got me to your channel. Thank you so much!!
I have very little knowledge, but I found your video very novice friendly, I performed the same video chip test so I took a pint with what you said and ordered a TZX651. My soldering skills are fairly primitive but I now have a working toastrack!!
Thanks again :)
Cool. I`ve got the same 1.4 voltage. I`ve already ordered the 2 transistors so this confirms there is a problem with them. Great help.
Fantastic repair session with 4 failing components! Thank you very much, since I learnt a lot from just this video!
Glad it helped!
So much destruction leads to one conclusion as to cause and you did mention it earlier in the video. Plugging something into the (totally unbuffered) expansion port while the machine is powered up is a huge no no and that is almost certainly what happened. I saw it so many times when repairing the 48K machines back in the day.
Yes, almost for sure that's what happened.
Great video again, Noel! Really enjoyed your methodology in diagnosing and fixing the issues.
Thanks! I'm really glad you enjoyed it.
Man, your videos are awesome. I just find it amazing how you teach everything with ease. Thank you!
Great stuff . Im doing a 128 plus at the moment. Will watch tonight . Thanks Noel.
Hope you enjoy it! Good luck!
I honestly thought you said nipple edition :-) wasn't sure what to expect. Keep up the good work.
Awesome repair job and well explained and logical process. After watching that, I've subscribed.
Hat off to you sir! This makes it understandable how to deal with large problems.
Thank you!
Another remarkable repair video from Noel (or is it Noël?). Your channel deserves far more subscribers.
Thank you very much! It's just Noel since we don't have ë in Spanish.
I remember having this picture of a transistor in my head since I was 9-10 years old, because my big brother used to make many DIY electronic circuits back then. The only thing that wasn’t adding up to that picture until I went to uni, was how a big current could flow between the collector and the emitter, when both diodes between the emitter & base and between the base & collector were facing the opposite way. A simple way to picture this, is that the base junction (P or N) is very small in size compared to the other two. Once you run a small current between the collector & base for example on an NPN, the electrons of the collector’s N junction will flow to the base and fill the holes of the base, leaving enough electrons to jump across to the other N junction of the emitter towards the ground. The larger the “small current” between the collector & base, the larger will be the current flowing between the collector and the emitter, through the load that is inline with them. That’s the basic function of the transistor as an amplifier.
Gran video Noel, estoy aprendiendo muchísimo sobre electronica retro, y técnicas de reparación, tengo un "Toastrack" y de momento funciona genial.
Gracias por tus videos.
Me alegro un montón! 😀
famous last words "common fault" :)
Haha, so true. I really thought this would be a 5 minute video. Show how to check transistors, fixed. Oops.
@@NoelsRetroLab people are "funny" about old machines.. but they are like old cars , it's got to a point where they need to have preventative stuff done. I need to get a new "modern" apple 2e psu , for example.
I was never into the Sinclair computers, so I know very little about them, but I find your videos and knowledge very engaging. Your need for sockets is very nice to see, even if you are using the inferior leaf spring sockets. And your meticulous clean-up of flux is also nice to see, so many old hack jobs left flux on everything.
As long as they are dual wipe, IMO spring sockets are better than turn pin. Turn pin are designed for turn pin legs rather than standard ones.
Excellent video, Noel! Inspired to pick up troubleshooting on my own poor blown up toastrack again!
And 16:08 : Too bad it's not a nipple edition indeed 😂😉
Awesome retro computing channel, Greetings from Poland! :)
Thank you very much!
Excellent videos and I want to add how much having those diagrams showing the pins being checked makes a difference. Thanks :-)
You're welcome! It's super useful to get that kind of feedback, so much appreciated.
Nice work and very fine explanation, greetings from Spain!
Thank you very much!
at 9:59 nice new transistors
when I was in high school (back in Soviet times),i had to repair the spectrum 128. more precisely, it was a clone developed in the USSR. it was called "Pentagon" (because one of earlest the pcb have five corners ground field). this clone did not have ULA, and instead had many chips (counters, multiplexers, logic). the fault was caused by an incorrect power supply (Chinese 7805). first of all, all memory was burned out. memory-related multiplexers have burned out. the memory page Manager burned out... the highest bit of the address on the Z80 also burned out, but the processor remained alive. in the original zx128, the repair would have ended up replacing the ULA and Z80, but I had to spend a lot of time finding every faulty chip. I didn't have an oscilloscope, instead I used an old tube TV (as an indicator. connecting the video input to the inputs/outputs of the chips). there were no other options. .....didn't have any money for another computer. the repair was completed successfully.
\ \ \ it was very interesting to watch the repair of the original zx.
Very interesting! I definitely want to learn more about the soviet Spectrum clones. I do have a Pentagon kit I need to assemble one of these days.
Fantastic video, got a +2 that looks to be blown in a similar way. I'm not prepared to send it to silicon heaven just yet (not without a fight at least). Great diagnostic tips, much appreciated.
If the +2 is a gray one, then it's almost identical to this one and you should have a pretty good guide. If it's the +2A, then all bets are off because it has the massive ASIC that could fail and leave you stranded (although the RAM and the Z80 tend to fail before). Good luck!
@@NoelsRetroLab Thanks, it's a grey +2 which is more or less the same just with a different layout. Very early PCB timestamp (8628). Judging from the the S/N it must have been one of the earliest batches of this model. It even has some bodge components placed on the solder side which are supposed to be there :) Hopefully it can be brought back to life.
Great work. New fan. 👍
Awesome, thank you!
Nice video Noel.
Thanks! Glad you enjoyed it
Very nice video. Your explanations are very welcome :)
Thank you! 😃
Great video ! Nice explination
nice job..thanks for sharing!
I know you're saying nibble, but I kept hearing nipple. I'll go get my brain from the gutter....
🤣
love your channel!
Thank you so much!!
Looks like that transistor went out big style.
Well, that gave you the run-around. :)
Great Video
Thanks!
I would not have expected that you were taught "conventional" current flow. I learned electron flow back in 1974/75 when I went through training in the Navy. Either way is fine, as long as you understand what's going on and can apply sound troubleshooting principles (something you've very seldom had any problem with!)
Great channel great video! So was that ram chip faulty or was it all the BIOS chip?
Wow, how many breakdowns for just hot-plugging in peripheral. This action is something that we have gotten badly accustomed to with today's electronics, but disastrous in retro. Thanks for reminding us of the consequences ... although I probably forget it and I will connect the external DDI-1 floppy drive to my Amstrad CPC464 on without realizing it. :-)
The Amstrad is slightly better because the connectors that go on the edge connector have caps at the ends, so you more or less are forced to put it in straight. On the Spectrum it just has a guide in the hole (and that can even be lost) so it's very easy to have neighboring tracks touch each other. And since one of them is +12V... bad things happen then.
Hi, found your videos a couple days ago and slowly getting through them, they are great!
Just one quick question, which scope are you using for probing the busses and clocks?
Thank you! Glad you're enjoying them! The scope I use is a Hantek DSO520P. Nothing too fancy and I think I even bought it second hand (hardly used) but it's great!
Very instructive, takes me at a higher level to test defective boards. I liked the way to test the databus and the address bus. Now i have some reference.
For the RAM chips, someone made a RAM tester and it works great. Did you find a replacement ULA or did you use the original one again. ULA is somewhat hard to find these days.
Glad it was helpful! I usually just test on the board with ZX Diagnostics, but like you saw this time, sometimes other things interfere with normal functioaning. I've made some testers in the past, but nothing permanent. I ordered a very complete DRAM tester a few days ago, so I'm sure I'll be showing it off in some video :-)
Wow so many problems on one machine. Glad you got it figured out. please keep showing the oscilloscope and multimeter. It is great to actually see on-screen what we should be looking for. Have you ever been on bytedelight.com. They sell all kinds of spectrum mods. I just ordered one that uses the back port to connect with a rasberry pi to create an hdmi signal.
Thanks! Yes, I'll definitely continue showing that. Bytedelight is awesome. They have all sorts of great things. I want to get one of their diagnostics boards one of these days.
That exact CPU is still made new and NOS. Also might want to replace the power jack with a gold plated one just for better transmission. The composite mod would also make the display much cleaner and you can get small composite kit boards for around $10 USD.
Great video as usual, thank you! It would be nice to see how those Data lines are supposed to read now that the ROM has been replaced? :)
Great suggestion! I'll do it in the followup video, although be ready to be disappointed because I think they'll still be "ugly" looking.
Cheers! I'd be curious to know how that works to prevent false readings.
I am not an expert on this but could it be the oscilloscope impedance affecting the signal itself? I seriously doubt it as it's such an old and slow machine, I think that happens on much more sophisticated and high-performance circuits. But I also struggle to understand how that ugly signal can be properly decoded... Food for thought!
@@tony359 Oscilloscopes are designed to offer theoretically infinite resistance/impedance. Practically it should be in the megaOhm range. So, not really.
Also, the signal would have to be really really square. Those slopes are problematic. If the design is problematic or something that can't be helped with (e.g. long signal lines), the usual fix is to intersect some Schmitt triggered buffers along the line. That's very common practice in modern circuits, even in memory controllers or, say, PCI-Express drivers.
@@tony359 We'll have a look at the data bus signals working in the next video, but even if they're ugly looking, there's a certain threshold after which they're interpreted as a 1, and otherwise a 0. As long as they're not hovering around the middle, and the rise/fall quickly enough, they're usually fine. But yeah, for some reason, I seem to recall the data bus on the Spectrum always being rather ugly looking for some reason (even with fresh caps).
I have a ZX Spectrum 48K that broke down because of the power supply went through a wrong switch cable and it reversed its polarity. It instantly destroyed the 7850, but after that being replaced it had very similarly symptoms: bad ROM, partially damaged ULA (working but after a while bad video signal) and bad Z80.
Yeah, if you're not lucky, it blows a lot of things (those are the usual suspects, and notice those are closer to the power input). If you're lucky, a RAM chip blows up really bad and saves all the others 😀
Hi Noel, nice video! With the final culprit being the ROM that seemed to corrupt the memory test of the RAM chips, did you happen to probe the data bus lines after the ROM change? I was curious whether the waveforms looked any different before and after. Do you think one or more of the ROM data pins was stuck high or low?
Thanks! The busses looked fine when I looked at them, so it wasn't just a bit stuck on high or low. Also tests were failing in different ways every time. Maybe it was a short that was lowering the voltage in some bit and wasn't being interpreted correctly as a 1 all the time? I looked at the bus afterwards and it looked the exact same messy way.
@@NoelsRetroLab I figured you looked! The data bus appeared as open-collector outputs with pullup resistors, the way they drove sharply to ground but rose exponentially to Vcc.
@Noel's Retro Lab : How are the data buses after the ROM replacement, are they more "straighten out" ? Asking cause i have some similar problem on a clone Z80, and i have the same suspect (ROM). I don't have the test cartridge to try it on(heck, i don't thing they are even compatible).
I don't remember for sure, but I think they were still kind of similar. The ZX Spectrum ones always look really "ugly" for some reason.
Wow!, that really was a mess :-(
If it was a 48k speccy, all the ram chips would be hotter than hell lol :-D
Yeah, seriously! The low RAM of the Speccy sure had a lot of problems with 3 different voltages feeding into it.
I would look for a replacement for TR4. Something with similar gain but higher power dissipation.
How many people would have given up on such a repair? Your endurance in those difficult cases is great. I wonder how many Specrums would be in running condition today if you were the one who did the repairs.
Haha, thanks!
I must echo other commenters that your transistor explanation is way better than text book explanations I have read (and reread, and reread, trying to understand) ... thank you!
I had to relocate a scene in this video to be sure I was commenting on the right video. You were testing a transistor with your multimeter while the transistor was still on the board. I always wonder about how to interpret the results of an "on board" test like that. Won't other components on the trace always affect the result or are there definite rules about certain results regardless whether the component is still on the board or not?
Thank you! I'm glad that was useful! I know I struggled for a long time to get a mental concept of transistors. They're not easy to understand intuitively.
As for measuring them in the board, what you may be able to do are comparisons to working transistors in working boards. Normally you expect to have a small drop one way, and no connectivity the other way. As long as the board doesn't have a path connecting those two that is less than the small drop, you should be able to do some good measurements (if it's shorted, something is bad, if it's much higher chances are it's also bad).
The one with no connectivity, as you saw, the Spectrum has a path with some connectivity between those two pins, but it's always about the same. So if you measure it and it's a short or very different, then it's also a hint that it's bad. You can then take it out and measure it, although it's also possible for the measurements to be fine and the transistor still not act correctly, but that's more rare.
Hi Noel. I have a Speccy +2 Grey with the same issue that the 128 Toastrack that you are repairing on your video. I know that essentially both are the computer, but I see all the components misplaced comparing with the board of the Toastrack. It lights the Power led and the cassette drive runs when a key is pressed, but nothing else...
I wonder if the transistors you repaired are the same or not. Perhaps with different names too...
Some idea?
It could be. It has a very similar voltage-generating circuity. Check to see if you have +12V and -5V. If those are stable, then the transistors are fine, but it's a great place to start. Look for the +2 gray circuit schematic to know where you should be getting +12V and where those transistors are. Like you said, the circuit is almost the same, it's all jumbled around.
Very didactic!
Thanks!
Repaired a c64 a year ago to play with it. I now want to get more retro Computers and try to repair them for fun. Btw I see you do a lot of desoldering, what gun do you use for desoldering? I’m thinking about getting one because desoldering with braid is pretty annoying, atleast for me😅
Nice! Once you open one up and fix it, you're hooked. That's what happened to me 😃
Being able to desolder quickly and safely is great. I use a desoldering station ZD-915. Highly recommended!
A Nibble😏 thats 4 bits as I learned last Wednesday.
That's right. Smaller than bite (or byte) size! 😜
Hola Noel, saludos desde Colombia, dónde consigues los chips de reemplazo para tus reparaciones?, Quiero iniciar mi negocio de reparación de computadores retro.
Gracias por tus videos, son exelentes
@3:42 A question: You said, that you would measure pin 11(VCC) against ground. No I wonder, since the schematic shows only 8 pins on the right side (where pin 11 is), but the soldered TEA 2000 has 9 pins on each side and all seem to be soldered. How did you know, that you had to measure the penultimate pin against ground?
Hi!
I replaced the membrane on my ZX Spectrum 128k+ "Toastrack" but it doesn't work, just the start screen. Can you please tell me what's wrong? Thank you
you should show databus signals after repair) also there is chineese component tester (TC-1) it can test a lot of components really fast (transistors also, and it shows actual punout of component, and other parameters (h21 and so on)) i think its`a good cheap solution. For high end - there are infrared cameras (seek thermal and others) that can show u which component is faulty even if its barely hot (29 deg celsius for example and others are 26)
Hi Noel, I have a 128k "Toastrack" that's basically stuck on the menu screen. The keys register as I hear the beeps when pressed but I am unable to scroll down on the menu, nor will pressing enter do anything. Do you know what could be the problem? The system work fine before, only recently has it started acting up and I can't find anything about this issue online.
my first computer was a Sinclair zx81, until i upgraded to spectrum 48k 😁
Nice! The Spectrum must have felt like a super-computer after the ZX81 😃
@@NoelsRetroLab yeah it was 'next gen' 😂
At the beginning - current 666 mA, hell's power supply :)
My spectrum 128 k still working my friend...
Noel, where do you get these awsome T-Shirts? (writing from Germany)
Since I got (or reproduced) vector logos for most systems for the boxes in my collections, one day I decided to put them on shirts as well :-) www.latostadora.com/regalos/?tienda=retrolab Edit: Fixed link.
@@NoelsRetroLab thank you very much! this link works for me (hope "retrolab" is correct) www.latostadora.com/regalos/?tienda=retrolab
@@Phenomz75 Yes, that's right. Weird, maybe the other link is only while I'm logged in or something.
:_( I miss my old ZX Spectrum 128K
Something which I've always thought was n 'issue' when I've seen it on older boards is the 'warped' traces on the underside. Is this normal? I always thought it belied corrosion underneath the solder resist.
Those undersides of the boards are normal. They seem to be mostly extra solder on ground traces. Sometimes you end up sucking some of that away when you use a desoldering braid on a ground pin. I kind of recall reading somewhere that that was on purpose, but I don't remember the specifics.
what the model number of your solder remover you used on the Z80? nice vid man.
It's an ZD-915. It's pretty great for the price. Highly recommended.
@@NoelsRetroLab awesome, thanks man, lookin for something just like that.
@@NoelsRetroLab Yes! I have a goot TP-100 (the real deal, not a clone) that is horrible, in every solder removing operation (1 pin) the dessoldering gun gets cluttered. Need to use the pin cleaner because I can't remove solder from the next pin (using that thing at 380ºC). Not recommended at all. The price of goot TP-100 is almost the double of ZD-915
@@JorgeCarvalho_web_dev Are you maintaining it and cleaning it well? At first I didn't know how to do it very well, and once the filters got clogged up, it behaved like you're saying. Now I keep it all clean and it sucks like a vacuum cleaner.
@@NoelsRetroLab Well, I have removed one filter from the "solder container" hopping that it would give me some more sucking power :-( What didn't happened... I have already bought a new tip because a little solder got stuck in the middle and I broke the cleaning pin trying to free it ;-( I clean the tip using the cleaning pin with a little Amtech NC-559-ASM (not the fake ones). It is the only thing that helps cleaning it and I wash the solder chamber... Dont know what else to do.. maybe buy a new pumping motor, I have used the dessoldering gun only 20 times, the results are so bad that I gave up. I use the classic mix of solder sucker, iron and a little hot air to help releasing the more complicated pins.. Sorry for my english, I am from Portugal
one transistor fail took 4 chips dead amazing!!!
I don't think it was the transistor failing, it was the overvoltage blew up the transistor AND the other chips.
how interesting thing... the ROM, I would never figured it out.
Honestly, it's not the first thing I would have thought about, but it was the only thing left socketed connected to the data bus so... might as well start there! :-)
Had that failed, the next thing I would have tried would have been the AY chip.
If all this damage was done by connecting something to the user port, I wonder if it's possible to modify the board to protect it from such things? Maybe add diodes to avoid voltage coming in on the wrong pins?
Good question. I've done things like that on an Amstrad before to avoid accidentally plugging in the 12V connector. Here is trickier because when you connect an expansion board, you can temporarily connect several neighboring pins to 5V, so I don't think diodes could save us in this case.
Possible decoupling cap issues with those terrible rise times. i.e. low or no local voltage reserve. Pretty bad. I've seen some other scope traces where it was clear the decoupling was a problem in some other video's. One chip's signals shouldn't show up on the trace from another as a minor dip.
does anyone know what computer the 1084s monitor was most commonly sold with? I have a computer in a very old very worn and stuffed original box in a storage shed, and while I can remember the 1084s from the monitor I can't remember if the computer was a C64 or some sort of amiga(as its been many years since I looked at it and its a fair distance away, I remember it came with a bunch of expansion stuff(extra disk drive, ram expansion(that doesn't work anymore)) and the computer worked, but I had to bypass the power switch on the monitor, and the main OS floppy disk had a bad sector and I couldn't copy it due to formatting problems(basically I couldn't make a new disk with my PC floppy drive the format it uses isn't pc compatible) it used 3.5" floppies
additionally, is such a computer worth hanging onto? while watching video's on old retro hardware repair is interesting, actually doing it myself/using it hasn't been for me for many years, and its taking up space, space I'll need to reclaim sometime in the next 6 months
I thought it was the Amigas (probably with different models), but I'm not an expert.
Oh cool, some Ferranti chips. I've got a rotary GPO phone that Ferranti made. Can't remember the exact year of the phone, but its probably a similar age to those chips
Yes, all the Sinclair ULAs were made by Ferranti I believe. That's actually all I know them for. I didn't realize they did rotary phones!
@@NoelsRetroLab yeah, the phone is a gpo 746, made in 1980 (20 years older than me :D ). I believe the company are still around, doing high quality PCBs and things like that
cool video..i Just bought a toastrack off ebay..( untested) hope its not too broken :O)
Fingers crossed! 😃 Good luck!
Wow, how could so many parts fail at once?! Do you think maybe somehow static discharge or a power surge could have zapped it?
I think the expansion board might have been plugged in and out multiple times.
@@NoelsRetroLab Once would be enough if the machine was powered up when the board was plugged in.
Why my zx spectrum with the composite video mod gives a good image in some lcd TVs, but gives very bad image quality in other lcd TVs?
Not sure. What kind of bad image? Dark? Out of sync? Noisy? Maybe using the capacitor or transistor mod variations could help with that.
Dryed up capacitors around the video circuit? Maybe try an upscaling device?
No doubt your LCD TV is HDTV. So the native panel is HD, either 1280x720 or 1920x1080. When you feed a composite signal into a modern LCD it must be digitized, de-interlaced, then unconverted to HD. You are probably seeing the quality differences between various manufactures up conversion circuits. Now I think our host here said there is an RGB output available from the ZX. Most LCD TV's have a VGA input. You would need an adapter cable and possibly some simple circuitry if the sync signals are the wrong polarity to make the transition. I don't know the ZX but perhaps someone else here could help you with an RGB connection to your TV.
I connected my ZX 81 to the wrong power output, it got 24 V. Not functioning anymore. Is it now completely toast? Can I try to save it ? (Or let someone save it bc I'm without electronic know how?)
Ouch! I will definitely need some repairs. If you're lucky, it was just the RAM that blew up, shorted, and protected everything else. If you're not... it could be multiple chips. You should definitely get it repaired somewhere though (or use this as an opportunity to try it yourself--that's how I started!). I have a couple ZX 81s that need repair, so I'll probably make a video about it in the next couple of months if that helps. Good luck!
Don't be silly, I'm not going to try and fix my computer: I'm going to send it to you :)
is the base always the middle pin out on a transistor ?
Not always unfortunately. When in doubt, check (and re-check) the data sheet. It's easy to get the leads wrong, especially if you're switching to equivalent transistors.
@@NoelsRetroLab haha .. hence my comment :-) .. just in case anyone else was wondering .. or just copying
Hey Noel, Karl from the UK here. Just recently found you channel, and i Just wanted to say how awesome the videos you make are. Have you heard of a UK youtuber called Retro Man Cave? He's also quality, would be great if you guys could collab sometime. Keep up the great work, and thanks for the great content. :)
Hi Karl! Thanks so much. I really appreciate the comment. I'm a huge fan of Retro Man Cave, of course! (check it out, it's in my Favorite Channels sidebar). I would absolutely love to do some kind of collab with Neil sometime :-)
One of these days I'll try to fix my C64... :(
Something a little odd is that the ROM in both machines is an EPROM.
Something to try would be erasing and reprogramming it.
That's actually normal. This is the 128K Investronica model, and I imagine they were in such a rush that they just used EPROMs and put the hand-written sticker on top. I just did a quick search and I see that the UK version used regular ROMs.
I was taught electron flow not conventional flow like you use.
Is there a common cause to this many failures? I'm a bit confused.
Probably someone either plugging in the incorrect voltage, or shorting everything by connecting a device on the edge connector while the computer was on.
I enjoyed the video, but for a ZX spectrum.. there's always the point where you have to think why continue?
Make a new board with an FPGA.
With a regular Spectrum perhaps, but this is the somewhat rare 128K Toastrack. It's worth any amount of work to revive it 😃
Why don't you touch the top of the chips? More often than not the failed components get super hot very quickly, especially RAM. It could save you some troubleshooting time. I learned that from GadgetUK164's videos. Recently I purchased FLIR One Pro, it makes finding the failed components and shorts much quicker and easier.
I did but must not have shown it or talked about it. Nothing stood out as getting warmer, but it's usually a great step. You'll see that in some of my other videos. I don't have a FLIR yet, so I usually use my fingers or a laser thermometer. How are you liking the FLIR? Is the offset between the heat and the image fixable or is it always there?
@@NoelsRetroLab I like it. The offset is fixable with a slider as long as you're taking a portrait photo, you can even fix it later on existing photos. In landscape it's bugged, the app still adjusts it vertically like it's portrait but should do it horizontally for landscape. Sometimes I still find myself taking landscape photos and realizing I can't fix focus on them so I have to take them again as portrait.
It would be cool to have you as a neighbour :)
😀😀
** ZTX651
Here goes the inefficient linear regulators again!
At least this time they didn't cause any trouble of their own :-)
16:06 I can make out the text "RAM FAIL 012345678".