Sinclair ZX80 / ZX81 / Z88 Forums

I found a short between 6 and 24 ... er... on the CPU that's pins... er... 33 and 37.

mrtinb wrote: ↑Sun Dec 24, 2023 4:50 pm This issue around the holidays, is what we call: White Christmas.

Ha! Good one!

OK - everything tones through to something and I can't find any shorts. It doesn't go to K, it just sits at a white screen even when giving extra time.

1024MAK wrote: ↑Sun Dec 24, 2023 4:30 pm Please check for short circuits caused by solder splashes on both the top and bottom of the board.

OK - so what you're saying is that it doesn't matter which address lines they map to... as long as they map to "an" address line.

Gotcha.

Will get out the probes now

I have made the link between the centre point and link 2, but there appears to be nothing "in" a link 1 to begin with, if you know what I mean.. because there's no jumper. ... unless there's a trace i've got to cut.

I'm trying to continuity test the address lines on this issue 3 board, and they seem to be jumping around. It's almost as if the memory expansion is mapping to the Ferranti rather than the CPU.

I'm confused.

OK ... I installed this mod... https://myretrostore.co.uk/product/zx81-internal-16kb-memory-expansion/ ...and I now get a white screen with no cursor. The fact that I got the same when I got the Panda working briefly, indicates that I could have likely damaged something on the motherboard. The follo...

mrtinb wrote: ↑Sun Dec 24, 2023 10:58 am Why not go full 64k with battery backed up RAM? It’s even possible to replace ROM area with RAM, so you can load your own custom ROMs.

Let me learn to walk first before I set off on a marathon

BUT... I'm reading about Hi-Res graphics... and ... well... if there's going to be no real benefit, then I won't and stick at the 16K... but I'd be interested to hear thoughts please.

OK - so reading things... there's no real gain by going for the 32 and I should stick with teh 16k because it'll be a lot easier. Yes?