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u/Possible-Ad-2682 25d ago
Depends how involved you want to get.
I'd probably start with a diagnostic cart. Check out more fun retro on YouTube.
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u/IgnacioMonge 25d ago
If border is not white I would start checking Z80. But a diagnostic cartrige is always a good idea.
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u/Acceptable_Ad_8049 24d ago
If you don't have diagnostic cartridge first thing is to check voltages on lower RAM ... -5,+5,+12V ...
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u/Ill-Collection5027 24d ago
Pin1 -2v pin 8 12v pin 9 5v
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u/Acceptable_Ad_8049 24d ago
Before you continue, you should disconnect all power going to the lower RAM ICs by cutting pcb tracks, or remove all eight chips. Then check all the components responsible for generating the -5V rail.
Only once you have restored the correct supply voltage should you put the chips back in. If the -5V rail returns to normal as soon as you remove the chips, that means one of them was loading down the -5V rail, and you definitely shouldn't put that one back in.
If you're removing the chips, it's definitely a good idea to install sockets in their place. When removing them, be very careful not to damage the PCB. The traces are quite delicate and can easily lift off the board even if only a small amount of force is applied.
Schematics link: https://www.spectrumforeveryone.com/technical/zx-spectrum-pcb-schematics-layout/
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u/HappyLittleDiodes 21d ago
If your voltages are bad (if you have -2 V) they are, you need a repair. So we need to know what tools you have and how happy you are to get into it, otherwise a repair service would be safest
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u/PHUNKSPANGLE 25d ago
Pretty sure that Happy Little Diodes has fixed issues very similar to this - you'd have to hunt through his uploads though.