Sinclair ZX80 / ZX81 / Z88 Forums

So, in that case I guess I have to swap out Z80s until I get one that works! Hope one of my spares does it! Annoyingly, I fitted a brand new IC into this Speccie to make sure it was reliable

Hi Paul,

That rings a bell, and I know I have read about this somewhere, but Google has not been my friend so far to remind this!

Hello All, I've just got my ZX Interface 1 upgraded (thanks to Ian Gledhill at Mutant Caterpillar, who did an excellent job) to a cool running vLA1 and the version 2 ROM, and it works just fine on my Harlequin. However, it is not paging into my original ZX Spectrum 48k which is the computer I want t...

Hi Folks, I'm just finishing off sorting out this Issue 3B PCB that is in an upgrade Spectrum + case ready to put on eBay, and I was wondering whether anyone knows the purpose of this little bit of extra wiring? All the resistances and voltages from the coil are spot on, and I'm not going to fiddle ...

Hi Distant Star, Just a quick response from my experience, and I'm sure there are many other more experienced people who will also respond. Your voltages all look okay to me, although the -5V is a bit low. I'm looking to do something similar to rebuild a spectrum from components taken from a board w...

Hi Mark, I've lifted one leg of C65, and the image is a little more stable, but still mainly chaos. Also, as the (hopefully) attached video shows, after about 5-10 seconds, the video signal drops out entirely. I suppose this means that IC14 is part of the problem, but that there is something else ca...

Another update…. some progress, but still a long way off! I’ve now redone the DC-DC circuit on this board, following Mark Morton’s approach, and now get 11V + to IC14 pins 14-16 and pin 8 in the lower RAM chips. In terms of voltages, everywhere I have tested is right where I would expect it to be. I...

An update on a productive day of sorting stuff. I’ve just got another Issue 3 board working, with keyboard clicks and response to a BEEP command, but the SPECTRA is still not feeding any video or audio output to the screen, so it maybe the SCART lead that is not behaving. I’ll try and check that thi...

Oh, and I forgot to mention, having left the computer on for about 10 minutes, none of the chips or transistors have become hot, all have reached lightly warm at most….

All the Lower RAM tested fine for resistence and voltages, as previously mentioned.

Cheers,
Simon

Hi Mark, Thanks for all of these. I currently only have a multimeter, and a diagnostic ROM for when a video signal is actually working, although I’m planning on getting a cheap mini oscilloscope and a logic probe this month (this might be the steer I need to actually order them!) So, some answers to...