Sinclair ZX80 / ZX81 / Z88 Forums

Thanks for this, it'll be very useful for those fault-finding colour related issues. If only this had been posted a few weeks earlier

JD

Yep, its just a crystal - same as transplanting any other component. I'm surprised it's not the ula with there being no difference in voltage on pin 16, that makes little sense.

I guess sniffing around ic14 makes sense, but I'm still confused by pin 16 on the ula...

JD

Doesn't look great, mine failed high with pin 16 at just under 4v, but I'd definitely expect it to vary. Seems these ULAs are fragile things! I got hold of a Nebula from Retroleum and that worked great, plus you no longer have to worry about replacing the socket as they now have fine pitch pins. Sti...

Set border and paper colours the same, then work your way through the colours measuring the voltage on pins 15-17 on the ula and post the results - it could well be the ula that is faulty. Alternatively replace the lm1889 but I'd do the ula check first as it's quick and costs nothing! Also check tr8...

Might be worth checking pins 15-17 on the ula, as well as the LM1889. I'd recap it first as dodgy caps can cause problems...

There's a few posts in here about colour issues, have a read

JD

Thanks for that, I did check pin 16 on the socket with no ula fitted and it was showing 0v, I'll do the remainder of the checks tomorrow. I just need to find a Nebula or vla82, noone seems to have stock which is annoying! I've actually quite enjoyed figuring out the fault on this, might keep an eye ...

Excellent, thanks for putting my mind at ease

JD

Hi,

Just putting a list of parts together to refurb this Spectrum +, it's a Samsung issue 4s board, would this already have the dc converter reliability mod done to it? Not sure of when this was done as a standard part manufacture.

Cheers

JD

Well, I've found the problem.... Swapped out the ULA from the machine with the fault into the working Spectrum I picked up, lo and behold the fault followed complete with 3.94v on pin 16. Re-fit the original ULA into the new Speccy, and it works fine. So, it looks like the ULA is goosed. Next questi...

Anyone got any ideas on this? I've sourced another Speccy, but before I do a ULA swap any assurances the higher voltage on pin 16 is not liable to nuke another ULA?

Cheers

JD