Sinclair ZX80 / ZX81 / Z88 Forums

Hi could someone identify the attached mod to a ZX80 I've just purchased
Not seen anything like this before
Kind regards Paul

Paul999 wrote: ↑Sun Dec 15, 2024 7:35 pm Hi could someone identify the attached mod to a ZX80 I've just purchased

Hi Paul. Can you please attach a photo that shows it

I've also moved this topic to the ZX80/ZX81 Hardware area.

Mark

now added files lol

Paul999 wrote: ↑Sun Dec 15, 2024 8:09 pm now added files lol

I don't see them

Are you trying to add them as attachments (either dragging into the text edit box or by using the attachments tap under the text edit box and navigating and selecting them), then waiting until the forum uploads them? If you don't wait, the upload will be abandoned.

Are they a file type that the forum supports (jpeg for example)? Are they under the maximum permitted file size? We prefer that you crop and resize large images unless posting the whole i.she is necessary.

Or are you trying to link to them. In which case, it needs to be a valid link to a website (not to a file on your own computer unless you run a web server).

Mark

think ive sorted it this time thanks

The board contains the following logic chips:

U1 74LS3? (I can't see the full part number)
U2 74LS93 4-Bit Binary Counter
U3 74LS00 NAND gates (4 x two input)
U4 74LS93 4-Bit Binary Counter
U5 74LS32 OR gates (4 x two input)
U6 74LS00 NAND gates (4 x two input)
U7 74LS00 NAND gates (4 x two input)

The two 74LS93 chips are different makes and so is one of the 74LS00 chips which is odd.

Date codes range from 1979 to 1980. So existing stock that someone had?

Only board marking on the silk screen that I can see is "REV A" which is not that helpful

Best guess is that it's likely a "SLOW" mode board, as that ZX80 has both a ZX81 keyboard overlay and a ZX81 "550" mask ROM chip.

Mark

I own some of these boards and can confirm its a slow mod making it a full ZX81.
A pitty what they did to this wonderful machine

hi ok thanks for the info, can it be reversed easily?