Sinclair ZX80 / ZX81 / Z88 Forums

I've fitted a couple of zeddies with Alliance AS6C62256 32k ram chips. Memory testing is happy with 16k present and usable by basic.

However, with a 220pF cap fitted it's not enough and if I go one step higher to 330pF I end up losing the left column.

I don't immediately want to write this off as a RAM issue, but I'm between steps here.

Grateful for thoughts and advice.

I just thought to tag a 220pF and 47pF together... and that still resulted in garbage on the screen.

I have not had to go above 100pF to get hires working. So far they have worked on 47 to 100pF

Lardo Boffin wrote: ↑Fri Mar 08, 2024 1:22 pm I have not had to go above 100pF to get hires working. So far they have worked on 47 to 100pF

Maybe Mouser are now selling duff chips!

I did try 47 and no dice. I'll try 100 and see what I get, but I don't hold out much hope. ... but that's one reason why I asked... at this point it can't just be a ram/cap thing?

I don't have any spare ferranti's to try either... I've got a couple of uLA81 on back order. No clue when they'll come.

This game is the first to use executable code in upper memory, but that should not be the problem

The lowres display is ok, problem is in the hiresdisplay.

dr beep wrote: ↑Fri Mar 08, 2024 1:43 pm The lowres display is ok, problem is in the hiresdisplay.

Correct. it's just the highres display that I can't get stable.

Incidentally, I use that game because it's quick to get in via tape.

Also, I appear to have a good clock. A little curved at the front and dipping below 0 on the drop, but hitting 5v at 3.25Mhz.

In case it matters for the price of fish, here's the clock as going in to the processor...

I can tell you exactly what value must be read but not ATM.
Tonight earliest.

I WROTE THE GAME