REPAIR FAIL - The worst ZX Spectrum yet
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- เผยแพร่เมื่อ 26 ส.ค. 2024
- So this repair began life with another faulty ZX Spectrum eBay purchase. At £22 I thought I'd bagged a bit of a bargain. Little did I know just what it had in store for me trying to get it working :-(
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Before installing RAM onto the board it's better to power on without RAM and no ROM and see stable picture with no flickering dots etc. As long as I remember there must be some black and white rectangles on screen interleaving like a chess board.
After that insert RAM and make sure you have vertical stripes on the screen. Pressing reset button should make stripes move. Only after this is okay, you can insert ROM chips. Or not to insert because you already know that something's wrong.
I bought an issue 6A board from what looks like the same seller - sold as "PSU fault", supplied with no ULA. Fitted a replacement ULA and it stil wouldn't boot. Turned out TR4 was blown (as expected), other than that it was IC12 which was the issue - but when tested for resistance with the board powered off, it *seemed* OK. Only when powered did that chip get significantly hotter than the others. Replaced that one and all seemed good, I left it on a soak test for a while with thermally printed labels on the chips and the label on IC9 discoloured in the centre - so I replaced that too.
Having worked on some other boards, don't discount the upper RAM - as that shares the data lines. I had one board which kept telling me one of the lower RAM chips was dead - when it was an upper RAM chip which was causing the issue. So on that basis, I'd remove ALL of the upper RAM and try powering it on again ...
I'm really glad you got it working 😊. From my experience, getting stuff that other people have had a go with just quadruples the problems. Not only are there broken IC's to find, but then there's the almost inevitable damaged traces to locate
@@RetroComputingRebootme too 😊I had to repair some traces on another board, albeit that was self inflicted - I was working with just a soldering iron and desoldering pump. Seems that with these boards, you either need to cut the chip out and remove the legs afterwards, or desolder as much as you can and use a hot air station to get the chip out. I've used the latter option quite successfully to remove, socket and refit the upper RAM on boards before. It's possible to repair the traces on the underside - allowing the sockets to sit flat to the PCB - but as you mentioned, that takes more effort - definitely worth getting some kynar wire for repairs though, learnt that lesson when modifying my old PS2 ...
If it's not the upper RAM, it might be worth checking for shorts and/or connectivity on all the address and data lines, from memory pin 2 and 14 of the lower RAM are connected and you should have similar resistance on pin 2 of each chip to ground, which might also help identify any faulty chip(s).
For the issue 6A board, I removed all the lower RAM and fitted sockets, powered on the board and then TR4 didn't overheat - so I knew it was a lower RAM chip fault. So I then refitted the lower RAM one chip at a time, powering on each time, until the faulty one was inserted - at which point the machine didn't boot and TR4 started getting warm very quickly. Turned off, removed that chip and then continued with the others.
Nice video and a great repair job, it's a shame that it didn't work but with so many faults and burned chips, omg...it was expected. And I know the feeling :) Cheers!
Thanks JosipRetroBits. I can't help but feel I was sooo close.....
100nF or 47nF for decoupling caps makes naff-all difference tbh. Could even go as low as 10nF.
Thanks Andy. I appreciate the feedback. Thanks for watching and commenting 🙂
Don't give up! We'rw all rooting for the Speccy!! :D
Have you replaced the Z80 and the ROM at the same time?
Thank you for the support 😊. I will be revisiting it. I think I just needed a break from it.
Yes I swapped out the ROM and Z80. I think there may be a damaged trace somewhere....
hey simon ..you did a good job! some of those boards are tough...i wish i could help you but i am a novice at this...i still enjoy your videos!keep it up!!😊
Thanks Mike, I really appreciate that.
I just had a bit of a pitty party and lost what my channel is really about - sharing my love of all these old relics. It really is about the journey, not just the wins.
I havnt given up on this board. I'll have more of a tinker with it I'm sure. It's just so much harder trying to fault find when someone has been there before you. I just felt I was soooo close to getting it working 😁
i agree...it does feel like you are really close...and again when someone else has been digging all over that board makes it even tougher..but don't get down on yourself...I like your videos ..my favorites are videos on your computers and games and those classic handheld games you have! great stuff!
@miked4377 Thanks Mike, I really appreciate that.
Don't worry, I've had a hard word with myself and there's plenty of stuff I hope you'll like in the pipeline 😁
They’re all dead Dave! 😂
I'm glad you enjoyed. I chuckled to myself at the time 😊
Omg - I’m at 9:48 and thinking you might better getting your other board going instead of this one.
Hi Mike, I think you're absolutely right 😂
Look how they massacred my boy
You've been made a mug by the seller. He's fobbed you off with a wrecked board populated with dead chips so he can claim "for parts"
There is a lot of it on eBay, scummy third rate board butchers making some money back from their failures.
You're probably right. Unfortunately it does happen sadly
no 1080p?
Hi, there should be SD available or 4k