Sinclair ZX80 / ZX81 / Z88 Forums

mikeh_nz wrote: ↑Sat Jun 03, 2023 6:02 pm I’d suggest reading this post as well.

That looks familiar! I remember reading that thread at the time as a visitor and thinking how lucky I'd been for everything to just work with no messing.

Looking at the way mine's set up, you don't need to isolate pin 27.

Yes. I'm not sure where would be tidiest, but pin 28 of the RAM IC goes straight to the +5V rail.

Lardo Boffin wrote: ↑Sat Jun 03, 2023 2:21 pmDoes the resistor just apply if using the full 32K? I’m only using the simple 16K version.

It applies to both as it's given as the last step of the 16KB mod instructions.

Pure guesswork on my part, but maybe it needs the same resistor arrangement as the 32KB mod I'm running?

http://www.zx81.de/english/32k-rame.htm

if you want to run HRG8, connect pin 27 via a resistor of 10K ohms with 5 volts

Hi,

What was the software mentioned specifically? Maybe someone can then point you to an alternative host.

Thanks Moggy. I wasn't sure on the 1K/2K RAM situation either as this one is clearly 1K. At least it's in a socket so I can upgrade it to 16K/32K internal RAM easily enough if it turns out to be a runner. EDIT: Having said that, I've just found 3x NOS Toshiba TC55257APL-85L on eBay for £10 delivered...

Hi guys, I've recently taken delivery of this US version ZX81 from a UK eBay seller for £25 delivered. Bear in mind that I'm based in the UK, so this was quite an exciting find for me. It was listed as "for parts or not working", but all ICs are socketed, so there may be some hope of resurrecting it...

I have an early ULA that only loads within an incredibly narrow range of accepted input signal voltage. It's randomly completely blind to 3V3 logic levels on the TAPE IN pin which I'm assured by another member here should work fine. The plan was to build an internal signal conditioner for this one, ...

Very nice. I like the authentic look of it.