Sinclair ZX80 / ZX81 / Z88 Forums

Mark

Fully working now?

If yes, well done

Oh, and welcome to the forum

Mark

Thanks a lot Mark, I'll buy the one you recommanded. Happy to help, but I think it was Paul that pointed to the ‘scope you are thinking of buying, not me. Yes, I live in England, in fact in the South-West of the country. I work for an infrastructure company and am classed as a critical / key worker...

For most 8 bit computers normally an analogue bandwidth of 20 MHz to 25 MHz is the minimum recommended. For the remaining 8 bit and most 16/32 computers (including Atari ST/STFM/STE machines), an analogue bandwidth of 40 MHz is the minimum recommended. That is an unusually low price for the specs th...

No, but if you have one, when some other components are added, it can be used for some testing.

Mark

Do you have a 4020B or a 4060B CMOS Logic chip?

Mark

I assume you tried the ULA and ROM from the faulty ZX81 in your known good ZX81? On your faulty ZX81, was this fault present before you carried out any work on it? Have you carefully visually examined the board, paying particular attention to the tracks near the chip pins. You are looking for broken...

Yeah, a MPS2369 is one of the few types that should be used, so it’s the correct transistor type.

Mark

I’ve posted details of the simple transistor based logic probe here . Due to its limitations, it has limited use on the CPU clock circuit. However by testing some of the other pins on the Z80 CPU, you can tell if the Z80 is doing something. As the ULA on the board that you are working on is in a soc...

Actual Testing on a ZX81 Z80 CPU Pin - Function 1 - A11 - both red and green lit 2 - A12 - both red and green lit 3 - A13 - both red and green lit 4 - A14 - both red and green lit 5 - A15 - both red and green lit 6 - clock - with the simple logic probe, only red will light 7 - D4 - both red and gre...