Sinclair ZX80 / ZX81 / Z88 Forums

I was having a look round for ULA's and found this.

This guy has got be be kidding right?

https://www.ebay.co.uk/itm/Sinclair-ZX8 ... SwxstgFZ37

Check out the silkscreen on the chip.

Hi You already have your answer to where the ROM should go. As said above, normally there is no need to renew the electrolytic capacitors on a ZX81, one (or two if an issue three board) decouples the +9V supply (this is mainly intended for when the ZX Printer is attached), the other is the capacito...

And you're not leaving until it's fixed!!! :lol: (Or until Lardo sells you one of his Chinese zeddy knock offs) Moggy hides fearing lardo's wrath It may be somewhat later in the week that I check with the RAM pack. I've no idea of the condition of it either so will likely open it up to check first.

As I said earlier I'm not the smartest here but I have seen similar patterns when the onboard RAM chip(s) were shot. The only way I could test was by using a RAM pack, which cuts out the onboard memory, as for for scoping and probing tests then hopefully a forum guru who knows their way around such...

Paul wrote: ↑Mon Feb 22, 2021 6:05 pm Ah, and if there is no picture from a PCB it's also a good idea to have a look under the cover of the modulator.

I don't get a picture per se with one of them, just a modulated plain black screen.

I very much suspect the ULA as I believe that creates the clock for the machine?

So the IC4 is the RAM?

I presume they had both sizes just to go for the cheapest at the point of manufacture?

Your second one has a quite early ULA at 8106. Nice. As most of the chips are socketed you could try swapping them around and may get a working zeddy. Thanks, but I'd rather repair them both. Gotta keep these 8bit machines running! I keep buying BBC's as 'spares' machines. But so far I've managed t...

Ok, so moved the ROM down to the bottom of the socket and switched it on.

Much different!

Now get the following...
Had to rotate the pic as it seems the site won't accept them vertically.

I'll have to remember to take the pics landscape mode.

This is no spectrum. The electrolytic capacitors are not critical. No need to change to get the Zeddys running again. The ROM will not be damaged if in the wrong position. But please don't turn them upside down. That will damage them. Cool. I note the two different boards caps are of differing volt...

Moggy wrote: ↑Sun Feb 21, 2021 7:16 pm Top picture wrong, bottom picture correct re ROM position.

I cannot help further than that I'm afraid as I don't have the Latin for things technical.

Ok, so if that ROM is in the wrong place on the socket, is there likely any damage caused to the ROM or other IC's/parts?