Fixing Other People's Bad Repairs (Again)
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- Опубліковано 3 чер 2024
- This episode is sponsored by PCBWay www.pcbway.com
Fixing computers is hard enough. But fixing computers other people tried to fix and failed... that's the stuff of nightmares and this is a perfect example of that.
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Tools I used:
- Bench power supply amzn.to/3PdKdh4
- TOPDON thermal camera (iOS) amzn.to/45jFMa1
- TOPDON thermal camera (Android) amzn.to/45BYGZm
- Hantek oscilloscope amzn.to/3Ew2wYJ
- Amstrad diagnostics ROM github.com/llopis/amstrad-dia...
Chapters:
00:00 Intro
00:32 Power
01:06 Inspection
03:11 Voltages
04:07 Temperature
09:23 Signals
14:49 Stuck test
19:53 CRTC?
26:11 ROM
31:46 Final touches
Music tracks:
Funky Stars by McKlain mcklain.bandcamp.com/track/fu...
Battro OST by McKlain mcklain.bandcamp.com/track/ba...
More awesome music by McKlain: www.mcklain.com
🛠 Tools I use ➤ noelsretrolab.com/tools.html
Connect with Noel's Retro Lab:
Discord ➤ / discord
Facebook ➤ / noelsretrolab
Twitter ➤ / noelsretrolab
Instagram ➤ / noelsretrolab
Mailing list ➤ noelsretrolab.com
#repair #retro - Наука та технологія
You usually make great videos. But here, it may be your BEST video!
There was everything we can expect for a complete repair: inspection with temperature scan, oscilloscope, voltmeter, then diagnostic with schematics reading, signal reading, Z80 assembly code, testing and finally trace repair, socket replacement, and chip replacement!
This video must be an introduction to anyone who plans to repair a retro computer.
Honestly, this one could probably have been done by a knowledgeable person without the use of a thermal camera or an oscilloscope. Having a good diagnostic cartridge and the source code listing of the diagnostic software is quite useful though. --- The best part about his videos, though, is when he explains what he is doing and why!
I admire your knowledge and patience. I'd have thrown that bad boy out of the window... :D Good job, fun to see and glad to see that you finally repaired it.
Yes, it is fun seeing the thought processes behind fixing someone else's 'fixes'.
Honestly, it seems like they managed to locate most of the problem areas. Might be as minor a mistake as assuming the board traces were fine. You know aside from the melted plastic on some of those sockets. --- Many people would have missed the issue with the single-wipe sockets used for the Z80 and the gate array, given that they look fine. Thoroughly checking stuff over is tedious, but it's the only way to be sure.
These are my favourite type of video, love the process. Always include videos like these in your output, so entertaining.
I prefer to view these mistakes as evidence of someone's journey towards becoming a great repair person, and helping to keep our hobby alive. It's easy to make fun of a botched repair job, but let's not forget that we all started with zero knowledge in the beginning. We shouldn't discourage anyone from trying and failing. That's literally what it means to gain experience.
Well done for your persistence and tenacity. You finding the intermittent socket connection reminds me of the movie "The Andromeda Strain" where the electronics technicians were looking for an electrical fault and the actual issue was a piece of paper! Turned pin sockets are not designed for multiple insertions and removals - when you first insert the IC legs they cut into the inside of the socket and effectively weld themselves, similar to what happens with wire wrapping. Unfortunately this process can only be relied upon once and after that if the leg is removed the cut can start to oxidise and will never make such good contact again. If a chip is likely to be inserted and removed multiple times it is best to use dual wipe sockets.
I so appreciate this diagnostic and repair saga: a heroic effort and win. Nicely done.
Thanks for sharing this walk-through. I really appreciate your perseverance and humility.
The first thing I noticed was the big blotches around the caps around the RAM, did he cook and de-laminate it.
My nightmare repair was a mate who managed to feed 240V AC up the main bus, blowing tracks of the board etc. The most amazing part of that one was the irreplaceable ROM's survived! So we fixed it.
After fixing the blown tracks, we then replaced any IC's that were red hot, then we replaced any that were clap cold, this got us 95% of the way. Boy was the dead pile big. However we were working for a telco, and using their repair facility, on their time - of course. Thanks go to all the telco subs that funded us......
This channel is great! Been finding a lot of these smaller channels lately and man are they good. Even the small touch of showing which pin your scope probe is on is just so thoughtful. Subbed!
That's why I love this channel, a real debugging!
Man what a journey. Some times it's appropriate to just take things apart to the atoms, check and rebuild everything. But very often that's just not needed because usually it's just a simple broken trace or chip that you just need to find. Probably a big reason why I love these repairs, you never exactly know what to expect :)
These repair videos are really relaxing. I hope you continue making more. Thank you.
Amazing as always. These repairings are helping you to get a bulletproof tester. Congrats on the mix between the board and the code debugging: so illustrative !!!!
So well done Noel!!!!!! Glad you fixed it, but to be honest, never got any doubt you would not get it running 😀 Greetings, Michael
Thanks 👍
Thanks Noel. I never thought cheap sockets are the problem.
I was screaming: "THE BOARD IS DELAMINATED!!!"
Always a delight when one of your videos appears in my feed. You sure showed that CPC who's boss :)
00:26 true Noel, its very enjoyable watching somebody else having a nightmare 😂
This is akin to my experiences of doing tech support (for Compaq in the late ‘90s).
I once got a customer who was told by a previous tech to reformat and reinstall Windows for no sound. All he had to do… wait for it… plug in his speakers! I wish I was making this up. I don’t know who was worse: the customers calling in or some of the people I worked with. lol
I had something similar in the past, also with a Z80 computer..
Broken via.. took me ages to find that one...
It was a wonderful episode!
Thank you for your hard work!
Not on a CPC, but in the past I have had faults that are fine when the computer is cold and then when things warm up and connections expand then the fault appears or visa versa. Intermittent faults are always the worst and require a lot more time and effort so well done on that one!
Yes, that's even worse! I haven't encountered that with expansion, but I did get a few problems that only show up after 5-10 minutes and they're a pain!
The first thing I saw was the de-lamination around the RAM. Somone used a paint stripper to get that ram out!
At first read your comment and I thought you were referring to some kind of chemical. But I think you were referring all along to applying too much heat 🤣 Yes, I think that's the most likely cause.
There's plenty of youtube videos with 'retro repair experts' delaminating boards with excess heat as they try to desolder chips using hot air and those godawful ZD918 solder suckers, not to mention their *awful* soldering when they try to put stuff back together.
Still, the more they destroy, the more my restro stuff is worth
First thing I saw too... A major failure right there with plenty of scope for fractured vias in the PCB too. I never saw that done to a double-sided board before. Goodness knows how much heat was applied.
Agreed, that's the first thing I saw too. Way WAY too much heat! This kind of damage will expand the PCB substrate and will break any vias in the affected area. I wouldn't even start to attempt a repair with prior "repair" work like that... but it does make for a good video 🙂
single wipe sockets cause SO much hassle - I replace them on sight in Amigas, whether theyre working or not !
I understand your pain. I tried to repair an Amiga 2000 (my own computer) which had battery damage when I had full on cataracts. I've since had surgery and I look at it now and see I've basically destroyed the board.
Fascinating repair. You could probably modify the diagnostic rom to stop the crtc check after a number of loops and display a failure message
In a past life, I used to do third-level phone support for software. By the time callers reached me, it's mainly to undo and fix what previous levels had done.
Boy howdy did they go off-script and do things that weren't sanctioned that I had to resolve for them.
Mmmmm bad sockets that fail depending on how you hold the board, almost like the classic "Is the computer plugged in? Is the cable sited all the way in?" but way more insidious and hard to diagnose. I can't imagine how hard it could be if that problem was originated on a cracked trace, doable but tedious and probably better to have a new PCB made.
BTW perfect Ñ pronunciation, pretty rare on English speakers.
I believe Noel is a native Spanish speaker and that’s why his Spanish pronunciation is perfect. He also has excellent English and I think he now lives in the United States instead of Spain.
Those read/write signals might look a bit ugly, but it's important to remember that for TTL inputs generally anything around 2V and above is considered logic high, and TTL chips by spec may output a logic high anywhere as low as about 2.4V.
So as strange as it may look, it may still be perfectly normal and within spec.
Great video. Glad I found your channel a couple months ago. Your recent TI-84/4A video finally made me order a video cable for mine. Now I just need to dig it out and hope the power brick still works. I know PSU mine came with had the in-line transformer which are usually pretty reliable.
Awesome detective work, Noel! One of the few channels I never fast forward, just too interesting all the way. And 10 extra points for the G7000 Videopac poster :) My first videogame back when.
Thanks! That's actually the label for the box containing a Videopac G7000. It was kind of getting in the way 😃
Back in the 1990s when I worked at a computer shop, we charged _extra_ for fixing computers which was a repair attempt from elsewhere.
Well done! That was a big repair. Great video.
Excelente video! Super difícil de diagnosticar alguna de esas fallas. Felicitaciones.
Yes that’s the stuff .. love the mystery and the twists of the fix .. very entertaining.. thanks mate .
Yay! A Noel's video to lighten my Friday, thanks! Too bad Ic an only drool over those beautiful machines as they are next to impossible to get in Brazil :)
Nice helpful video, even though I don't own an Amstrad computer, it was still helpful to see what and how you fixed it.
Touching a PCB making it work - that's called "magic hands"... :D
Nice one!
Ah the most comfy T-shirt ever, Steam Dev Days (2016 dark blue edition). I think that might have been the last time I saw you unless you went to GDC in 2017/18.
Right??? One of the best t-shirts ever! I haven't been to GDC in over a decade, so yeah, that was the last time. You need to come by if you're ever in the East Coast!
@@NoelsRetroLab Will do!
Noel did it again. An impressive repair. Well done!
Very well made repair video Noel. I enjoyed that!
This was super. I liked the 'boss fight' analogy at the end, too :D
Every time I try to fix an Amstrad it fails, to fit in the garbage can. lol.
I commend your patience. Great job!
Nice effort! Do you think it would be a good idea to change your diagnostic ROM to time out on the VBL and report that as a possible issue with the VBL line?
Just shows how skilled you are, Love the videos Noel.
1:30 looks like the PCB has been hot air desoldered to socket the RAM, and this has been done too hot/too long and delaminated the PCB ripping the internal traces/vias.
Great videos! Damn those single wipe sockets....
This video is a perfect example of why sometimes you need a working machine to fix a broken one. With my C64 I had to fix it blindly. The ram wasn't too hard. I knew exactly which one it was, but I replaced all 8 because it was mt ram. But then I had this wierd glitch. I for the life of me couldn't figure it out. I replaced the color ram. The PLA. Eventually I realized the voltage dropped too much but only when I had my U2+ cart installed. Then I realized my home made PSU didn't have thick enough wiring. That's all it was. New wiring = works fine....until the cartridge port gave up the ghost. De-oxit had been working for a while. But eventually de-oxit wasn't enough. I replaced it and the system is fine now.
If I had another C64 that worked, I could have tested the color ram and the PLA.
That is so true. People underestimate how important is to have a working one side by side. If nothing else, it helps me to learn the signal patterns under certain conditions and then you can backtrack into why something isn't working.
Great debugging, well done.
Wow, I mean I'd like to solder on my Amiga, but I'm going to make sure I practice a lot first on a random board. Also, it amazes me that the person didn't think how he/she might be the cause looking at the work itself. :)
amazing repair, thank you!
Noel, I hope you are able to bring us more videos on a regular basis as I like your channel very much. However I can understand with your work and move to the US it's not always easy.
Nice repair, well done Noel.
well done for getting it working. great video id like to see more repairs they are interesting
The flood of satisfaction the runs through you when you finally solve difficult issues
In some point of the program you should do a loop waiting for vsync but counting and report an error indicating vsync never received.
That's a really good idea. Just generally extending it to check all the PPI ports possible would be great too, but I may need to design a harness for that. Not sure.
or even a beep turned on before the loops, and off after
@@NoelsRetroLab At least the vsync is something you can detect easily, and it would tell you there may be a problem in ppi or vdp
Impressive video as usually now ! 😮. Thx.
Great! I would never have solved that.
Los demás mortales daríamos lo que fuera por esa habilidad para comprender el sistema eléctrico de un ordenador.
Felicidades eres un artista
Very interesting! It feels like following an investigation to find the criminal(s) 🙂
Well, that was my friend, who has since told me he wishes to remain anonymous (for obvious reasons 🤣🤣🤣).
I'm truly impressed! That you actually got it to work properly! Wow!
I also hope you weren't in Spain in the past months with the 40++C temperatures...
Thanks! No, I've been back in the US for a couple of weeks so I missed it. Phew!
I always enjoy your videos and is one of the evening highlights when I sit down and watch it with some snacks and enjoy your skills. You really have a great talent to explain what you are doing and what you expect happening.
Are you back in the US by the way?
Greeting from Germany!
Yes, I've been back in the US for a few weeks already (this video was actually recorded before my previous one, so things are a bit out of order).
Nice video, well done, thanks for sharing :)
Interesting that the disc-type capacitors were replaced by MLCCs. Typically they are quite robust, unless the disc cracks or so. And the MLCCs derate their capacity with rising voltage. It's probably no issue here, but I would have used discs again, especially since they are still in production.
Nice video! Thank you so much.
It wasn't one of mine. :) But I kinda-sorta do have an Atari 2600 in similar condition that needs fixing. Let me know if you want to tackle that. That said, I was able to fix two other 2600's so I'm not a complete nim. But great job on that computer. That was fun to watch.
That moment when using your code to find the bad trace on that logic IC *chef's kiss*
Wow, after all that fixing up other people’s mishaps!!! It’s working , great job, keep up the great content mate. 🤙🏼🇦🇺
Joe from Australia 🤙🏼🇦🇺
There is a certain… irony? to the fact that sockets are usually added to make things more maintainable, but are causing a maintenance nightmare because they were bad sockets badly installed.
17:37 when desoldering pin 10 you can see some sparks. I don't think this is normal.
I hadn't noticed until you mentioned. Those are definitely not sparks, but they do look like it. I think it's the melted solder and as I press the trigger, it flashes by for a split second, creating that illusion.
@@NoelsRetroLab "Sparks" could be a wrong word, but this definitely looks like discharge, it's clearly visible on freeze frame. You may have some grounding issues in desoldering gun.
Hi Noel, nice repair, as always! Where did you get that nice tool that you used to remove Z80 at 30:50?
Thanks! I don't know. I think it's called a crow bar chip lifter or something like that? It's just like a screwdriver with a curved tip. I don't know if it's exactly the same, but search for Wiha Precision Chip Lifter on Amazon and you can go from there.
Amazing job you did there🎉
Thanks! Some good tips I'm going to use to try and get my reproduction board up and running.
Thank you! I'm sure you'll be able to get the repro board working. Just keep plugging at it and learning.
Been there, done that! Except I'm usually the idiot who messes it up the first time around, trying to hurry through the troubleshooting process.
Magnífico como siempre. Una pena perder de España un crack nivel Dios como tú.
Oh my! That is some serious delamination on that poor mainboard!
Wow, great job. I'm both liking and subscribing.
Thank you and welcome aboard!
A Phillips VideoPac, nobody else has ever heard of one of those. My Stone Sling cheats.
Did you ever try the 16k eprom that came with the machine? Maybe it is a program for controlling some proprietary hardware connected to the CPC? (some old machine of some sort)
Thank you for very interesting video, second one in a row.
Looks like Spain-based videos turn out much more interesting than US-based for quite some time. Hope it going too change in future, so US-based video become as good as this one.
Ever tried to clean corroded contacts with flux? Flux is made for that too!
Aren’t the gate array and the Z80 working fine and was it just the el cheapo sockets that were the culprit?
That would mean that someone that tried to fix this computer probably did not have the old school knowledge of the era that PC came from. like installing a socket that wasn't used when that computer was originally built. I remember in late 70's, 80's and 90's, wen you used sockets that was for prototyping in electronics. And that was why they soldered IC chip to the PCB back in those days, improving the electrical connection. And also back in the day, they used lead in the solder, now you need to find new old stock of roll of solder with lead content. If not you are stuck using the new friendly solder, but you need to use flux to make sure the solder will flow and make a secure electrical connection. And that is why often we have to fix broken traces on PCB.
Not sure what you mean about the solder. New 63/37 solder is easy to find and I use it all the time. Can't stand the lead-free stuff. I think sockets are used more on old machines now because the chips are old and going bad, so it makes things easier to work on. You didn't really have that problem forty years ago when they were new.
Why at 20:50 does it say UNKNOWN CPC - is this because it doesn't know until it gets further along in the test but was blocked by the endless loop for Vsync check?
I'm always fascinated when people try to repair something by butchering it violently. So far I have never seen a computer where the initial problem was that it wasn't butchered enough 😁
There's a fine line between confidence and fool's confidence, and then not being confident at all. It looks like someone tried to fix this, only made it worse, they went down the wrong path and it went worse and worse until they eventually gave up. Sometimes that's how people learn.
And with through-hole stuff, no less. I can understand SMD repairs going wrong, but you have to be really careless to damage so much on an old 2-layer board.
@@Waccoon it's called a hardware store soldering iron that gets 600 degrees hot, meant for brazing together roofing drains. Temperature controlled soldering irons are thankfully getting more widespread but lots of people try and do soldering on irons really only meant for wire splicing.
When a craft changes to art.
the discoloration on the board is bit how ya doing.. looks like flux that has got into the board.. probably not much of an issue with no internal traces.. but still not good...
nice troubleshooting Noel..ive seen the same sort of thing from a single pin on the GA having a bad connection on the socket.. machine would run, but would randomly reboot itself..changed socket and its been rock solid ever since
Yeah, I didn't see anything obviously wrong with that part of the board, but the discoloration was odd. I don't think you can do that just with rough soldering though. I wonder how it happened.
@@NoelsRetroLab2 ways ive seen (with an old board that ive ripped all the components off!).. heat! these board really dont like it.. they are just fibreglass afterall!..you'll usually see scorch marks tho... or flux has seeped into the board
@@NoelsRetroLab I'd have to guess someone read bad forum posts and tried whatever disastrous chemicals they happened to have around the house. "magic cures" are all too common in the more religious part of the flock.
Would plugging in the power supply with the wrong polarity fry the chips in the way observed? Did you ever check that the voltage sag was gone at the end?
Good questions. Normally plugging it in with wrong polarity (or a 9V one) would fry the RAM and maybe the Z80. That's what I've seen in the past. Not the GA and other chips. But everything is possible! I didn't check the voltage drop at the end, because I know that with my PSU, for whatever reason, it's always around 4.6V or so, which seems really low. With a plain wall wart I get rock solid 5V, so go figure.
That looks like a really bad PCB delamination issue near the ram chips.... 🤔
I noticed that too and recorded some comments about it, but ended up cutting them from the final edit because I didn't see anything obviously wrong there and I've never seen any products cause that. I'm curious what it was though.
Just for my curiosity, what was in the 16k EPROM? What the computer would do with it inside? Will it boot to something or just show garbage on the screen?
I didn't think to check, but I'm 99% sure it was just one of the two 16KB ROMs needed to boot the Amstrad. They probably didn't realize it needed both of them (in the same chip).
Interesting. Thank you.
Will a CMOS Z80 work? I know the CMOS version doesn't support the undocumented opcodes found in the older NMOS version.
What is with the discoloration under the solder mask near the ram?
De-lamination -- too much heat.
Not those crappy Amazon caps!
Wow that was a pretty shoddy first attempt by your friend. Well done!
There is no excuse for still using that type of IC socket in 2023. Turned pins all the way!
The board area around the RAM is delaminated. Someone used way too much heat. That PCB is in a sorry state…
Yeah, you're right. I wasn't sure what caused that, but other commenters agree that's the likely cause.
Voltage regulators like the 78xx need a few volts to do their work. So if there is a 7805 in there you should supply it with 6v or so from the bench power supply. That way it has something to work with. You cannot set the bench power supply to 5v and expect the regulator to still supply 5v.
More likely a minimun of 7 volts is needed for a stable 5v output, there are versions that are stable with as low as a 5.5v but that is very dependent of the current.
no regulators anywhere on the original CPCs!..power coming directly from CC/CV bench power supply... always a bit of voltage drop on the board...
@@WacKEDmaN I'm not that familiar with the board, but Noel talks in the video like there is one on the board.
But even if there isn't, it's a general statement and valid for any place where a regulator is used.
@@bzuidgeest ..he said there is no regulators!.. and even put some words on the screen....
@@WacKEDmaN relax, it's always possible I misunderstood him. Instead of focusing on the presence or not of a vintage regulator. Let me ask you this (again). Do you want to claim that my general statement about the working of voltage regulators is in any way wrong? If not, then what are you really bitching about?