Sinclair ZX80 / ZX81 / Z88 Forums

I got new 4116 chips, inserted them all and the screen was still the same. So I tried 8 old but known good chips from the 'spare' Issue 2 (which is now also sorted, see below) and the patterns were very different. So, because it was already socketed, I tried swapping the 6C001E ULA for the 5C112E th...

I got my super-duper de-soldering solution and was able to remove the 8 lower RAM chips. Lifted 3 traces but was able to sort those in a neat fashion. Now it all looks good. What sort of screen should I be getting with no lower RAM installed? With empty sockets it's exactly the same as before with t...

I really feel I've learnt something here, about the various voltages on the Spectrum board and where they come from etc.

Well that's even more encouraging then. I may well do the DC-DC mod, but first I'll wait for the new RAM and see how/if it works with that. Thanks for now.

Right, well a little progress, although the screen output is unchanged. I changed C46, R55 is spot on. I changed C74 as a lead fell off. I also changed C61 and D11 (I currently don't have new diodes but stole one from a parts ZX81 - one of the keyboard connector diodes which have the same value writ...

Thanks so much for your time and expertise here, it's not the first time you've helped me with words of wisdom. I think I've done this right: On the input side of the regulator it measures 11.3v. The 12v leg on the RAMs are about 12.3v. Voltage measured on the anode side of D11 is -1.6v. Voltage mea...

Certainly, here it is.

On the 4116 chips the +5v and +12v was fine, but the -5v showed a small (0.4+) voltage on all of them.

My original Sinclair transformer puts out 14v (without load) so I'll also try a modern one that is actually 9v. Is it therefore likely that the TR4 and TR5 are dead? I just have a multimeter.

I also ordered the Retroleum SmartCard, perhaps that will help with one or the other.

Thanks for the replies. The border isn't white, it seems to be mostly red, but I do remember it being yellow or black too on various re-power-ups, but never white. I de-soldered (I'm ok at desoldering) the Z80, popped a socket on and put a known good Z80 on it - same thing, so put the old one back a...