Sinclair ZX80 / ZX81 / Z88 Forums

Further fiddling with the issue 2:

Fitted the -7 ULA, with the Retroleum rom card installed with an immediate improvement in colours. All RAM etc passes the tests.
Removed the card and whilst it boots, I rapidly get random coloured blocks, black dots etc appearing on the screen with an eventual crash and reboot.
Fitted a spare ROM from the donor issue 4 pcb in place of the original one and get the same, plus garbled text at the copyright message. Looks like missing horizontal lines from the text.
Both ROMs in the Retroleum card give a good solid boot screen etc.

Are we looking at pcb faults still, as ROMs in the external card work fine?

Put the original ULA and ROM back and again a good solid boot, but with dodgy colours. Think I’m going to have to get a 5C112E ULA to prove things. Anyone want to swap a tested 6C001E-7?

Just won a working issue 2 off eBay, donor ULA (and working pcb for comparison) on it’s way

Received the donor S2 motherboard. Swapped the ULA into my S2, same results, odd colours. Ok thinks me, my original ULA must be ok, or….. is the new one dodgy too?

Put ULA number 2 back in its socket and tested the new S2 motherboard on the big telly as it’s not comp modded. Guess what? Dodgy colours. Two duff ULAs??

Tried the 6C001E-7 ULA in the new S2 motherboard and with a bit of twiddling of the trimmers got good colours. Oh great, looks like both S2 ULAs are indeed dodgy.

Or do the early ULAs not like modern LCD TVs?

Good thing is that the new S2 motherboard runs fine with the 6C001E-7 ULA, so my original one does have other issues. I’m planning on removing the 48K RAM upgrade and seeing if it runs ok with the 6C001E-7 ULA. After that the lower RAM will get swapped out, but for that I’ll need to desolder etc …..

I’m almost at the point of giving up on my childhood S2 and just sticking with the new motherboard. I really want to fix it though …….

Not sure what made me do it, but I tried all my issue 2 boards on the jvc telly in the bedroom (no not loading any dodgy games involving Sam Fox lol)

Upshot is that they all tune in fine, including my childhood pcb. Nice solid good colours

Conclusion? Issue 2 pcbs are picky about what telly they drive. The solution if you have weird colours on yours is to use a different tv or swap the ULA for a later 6C variant. These seem to output a signal that is compatible with a wider range of modern tvs.

I now have several working systems, including the newly assembled Harlequin 128K that Santa got me. Most will be going on eBay, there will be;

Issue 6S, transistor comp modded and recapped, tested and working, all diags passed. This would have been my main board had the Harlequin not come on the scene.
Issue 2 as it came out of the factory, tested and working, all diags passed.
Issue 2 dead, no display. I guess I could try to get it working, but I really haven’t got the time. Someone else can have that challenge or use it for parts
Rubber key case, working recent replacement membrane. Dings and scratches, extra holes in the base where it has been screwed to a wall by a previous owner, no feet.

1024MAK wrote: ↑Thu Sep 07, 2023 7:48 pm If you have, can borrow, beg another TV, definitely worth it to save a wild goose chase.

Mark

1024MAK wrote: ↑Wed Jan 17, 2024 10:39 pm

1024MAK wrote: ↑Thu Sep 07, 2023 7:48 pm If you have, can borrow, beg another TV, definitely worth it to save a wild goose chase.

Mark

Yes, I really should have learnt from the last time shouldn’t I?

To be honest I’ve kinda enjoyed the journey, even though I’ve ended up with far more Spectrums than I needed ……

I also have quite a collection of 6C ULAs in stock for no good reason.