Sinclair ZX80 / ZX81 / Z88 Forums

Thanks for the confirmation, I'll raise an issue on the project's GitHub.

I went back and re-watched the Joulespercoulomb video and according to him the black pixels should be at 0V which they're some way off on your oscilloscope traces. Is there an easy fix for that? Is that what the additional 1K resistor was aiming to fix? I notice that the circuit with your fixes is s...

Opened up my working Issue 1 to test:
ULA pin 20 to +5V = 1.737
ULA pin 20 to GND = 0.768

So the values are pretty consistent. Which is odd because it kind of suggests that the ULA circuitry on the defective Issue 3 should be ok.

I secured the WESPI board to the bottom case using a strip of adhesive hook and loop fastener which worked well. I like having it hidden inside. Wolf in sheep's clothing

Hang on, looks like I measured my resistances wrong. I didn't realise it would be directional, and it only works with the probes one way around. Is that because the connectivity to +5V and GND is going via a diode inside or upstream of the ULA? If I put the negative probe on the ULA pin 20, and with...

I'm considering removing the ULA and socketing it, and then trying to buy a battered Zeddy on eBay to be a donor. Is this madness, or can it reasonably be removed - if for example I've previously managed to successfully remove the RAM chips without damage?

My multimeter reads "1." for both when I do that, which is the same reading it gives when neither probe is touching anything, so I guess that means there is no short of pin 20.

I have replaced C10. No change. R33 and R34 were measuring their correct resistances. All the continuity back to ULA pin 20 is fine. I used the test program linked above and it just detects zeros whatever is playing via EAR. I have replaced the 4K7 resistor at R33 for a 3K3 one and it made no differ...

Having seen the photo on page 1 of this thread of a Traco regulator installed upright I soldered mine in like this. That was a mistake. There are two problems. The upper case slopes down just at the edge of where this regulator sits, just enough to prevent the proper mating of the PCB to its standof...