Sinclair ZX80 / ZX81 / Z88 Forums

Here is my issue 3. The chips are socketed, but not by me.

Looking at some of these issue 3 boards,they seem to have a date code as well next to the ear socket.

And here is another issue 3, not socketed. I bought this in the hope of an easy ULA swap for mine to see if it cures my output issues but sadly it's not looking easy!
Lardo

And another issue 3, socketed but different to the first socketed issue 3 of mine above!
It looks like the ROM is in an oversize socket?
This one appears to be producing a rather good image without being composite modded. Once I get the keyboard fixed I will test that in a bit more detail.

Lardo

QUOTE.
"It looks like the ROM is in an oversize socket"?

From the factory any ROM socketed 81's came with a 28 pin socket, your other issue three has been converted by the last owner, I suspect, as issue threes were in the main not socketed possibly as a cost cutting exercise.

The top 4 pin holes on your first issue three are factory soldered over as the 24 pin ROM was directly soldered to the board at the factory.

Moggy wrote:QUOTE.
"It looks like the ROM is in an oversize socket"?

From the factory any ROM socketed 81's came with a 28 pin socket, your other issue three has been converted by the last owner, I suspect, as issue threes were in the main not socketed possibly as a cost cutting exercise.

The top 4 pin holes on your first issue three are factory soldered over as the 24 pin ROM was directly soldered to the board at the factory.

That explains that then thanks!

An issue one I happened across...
I like the agricultural feel of the heat sink!
So far I have got an output (dark background not surprisingly) and the keyboard works. Or at least it did until I took the case apart. Fingers crossed it still does when I eventually put it together again!

Not sure whether to composite mod this one or keep it original.

Unusually the case has a serial number 001-003011.

Lardo

Erk - bet that gets a bit toasty! Looks like a good candidate for one of those recom regulators, or one of these - http://www.ebay.co.uk/itm/272451377177? ... EBIDX%3AIT

I get the impression that the SN'ed cases were much later in the ZX81's life, perhaps they used returned/serviced pcb's in them? This is Sinclair we are talking about

Fwapp wrote: I get the impression that the SN'ed cases were much later in the ZX81's life, perhaps they used returned/serviced pcb's in them? This is Sinclair we are talking about

That would explain why a later case contains an earlier PCB. I guess it could have also been the previous owner - the screws holding the PCB in the case are missing.

Also a good chance of that as well