exxos's Atari, Amiga & retro forum

So my eBay ZX81 in a case arrived today and it's huge compared to the original!!!


Just look how big it is!!!

I need to check it over fully before I power it on, and it'll also need a comp mod as based on the eBay pics it's modulator only. More when I open it up, but I don't think I'll put the comp mod in the modulator can this time as there is so much space inside it seems rather pointless.

The keyboard looks and feels identical to the DK Tronics keyboard I had back in the day, so that's a nice win.

I've donated the Sinclair RAM pack that came with it to my ZX80, but as it happens the Memotech RAM pack that doesn't fit the ZX80 fits this thing a treat :)

Well, internally it's interesting.


The PSU is connected directly to the ZX81. So basically its a 5v PSU (Actually about 4.2v when measured) and there is no 7805 and the board has been modded to take 5v direct.

I'm wasn't sure if the PSU was regulated or not, but sometime you get a little surprise...


I think next I need to hook up a comp mod and see if it just works or not. I'm expecting it to need a back porch.

Interestingly the keyboard cables were wrapped in foam and I did wonder if there was some sort of PCB in there, but no, just a massively over engineered connector!!!


The keyboard is apparently from Mapli:


I need to get rid of all the masking tape, it's dry and crispy and not really much good for anything!!!


And a gratuitous image of the PCB for posterity and IC numbers:

I did the 5v mod to my Atom with an external regulated 5v PSU, so much less heat in the case and more reliable now.

Love the insulation used for the mounting nuts @rubber_jonnie

PhilC wrote: 09 Oct 2025 11:19 I did the 5v mod to my Atom with an external regulated 5v PSU, so much less heat in the case and more reliable now.

Nice. I'm a little worried the voltage is low, but I need to test under load. And it is about 4.7v under load, so all good :)

Also, it works:


So just needs a comp mod wiring in properly and not with clip leads :)

Icky wrote: 09 Oct 2025 11:20 Love the insulation used for the mounting nuts @rubber_jonnie

Yeah, cardboard and making tape is kinda 'What have I got in my bin' thinking...

Also, I found the remains of a fag packet under the PSU to shim it into place!!!

Very home brew, but a bit out of sync with the mega nice keyboard connector...

Love the DIY effect...

:D

HigashiJun wrote: 09 Oct 2025 12:07 Love the DIY effect...

:D

Yeah, very similar to the one I had back in the day.

And it's all back together:


And the last few shots before closing up:


I had a few problems getting the 16K RAM pack to work and ended up running my soldering iron and wick over the top to clean the edge connector. A bit of contact cleaner helped too.

Didn't know that you had a 7800+ as well as the 2600+ @rubber_jonnie

Is that another recent addition?

I've still not managed to get the 2600 junior you gave me set up and working yet...

Maybe in a month or so I will actually have some hobby time.

My last day at work is the 31st October.... spooky!

:D