Sinclair ZX80 / ZX81 / Z88 Forums

Hello, I am back, with my "Russian ZX80 PCB" build.

I am done building ZX80 kit (the one bought from Ebay, so-called Russian PCB), but it just does not start. I checked the following
1. Crystal, it is 6.5MHz
2. 2732 ROM modification, the PCB already has some
3. I did 555 based back porch generator
I got some sort of picture, so I presume CPU is working and it does read ROM, but something wrong with any of the rest of ICs. Unfortunately, I have no oscilloscope, so maybe there is a quick solution like replace IC 11 or IC 20 (for example). All chips are 74LS
Here is a video of the powered board, any advice would be welcome!
https://www.youtube.com/watch?v=6ulOMmdu0Dw

I have one of these but haven't finished it yet. Is that just a plain socket under the ROM? Are you sure the ROM is right? The kit that I got included a ROM chip (2732) but there was no data on it. I have a 2732 to 2532 adapter for when I make mine.

Can you provide a link to the website of the producers?
Was there any documentation with the board? We need to know what modifications compared to the original board were implemented.
Kind regards Paul

I can't speak for the OP, but I got mine on ebay from a Russian (who seemed to have Chinese connections). It seems very well made and as far as I can tell, it's (in terms of traces) an exact copy of an original. Here are some pics.

It came with all the IC's and crystal, most of which look 2nd hand - certainly the Z80, which has a 1994 date stamp. As mentioned, it included an EPROM (2732) that was non-programmed. I can't find any details on the producer or specific documentation.

I'm pretty sure the EPROM pinout isn't right for the board, i.e. the board has the same connections as an original, so I have an adapter for that. I'm going to steal a modulator box and the 3.5mm sockets from a spares ZX81, when I get round to it!

Thanks for the pictures.
I can send you new 3.5mm connectors (original) . No need to slaughter a Zeddy for this.
Just pm me your address.
Kind regards Paul

crrush wrote: ↑Wed Nov 13, 2019 11:03 pm Hello, I am back, with my "Russian ZX80 PCB" build.

I am done building ZX80 kit (the one bought from Ebay, so-called Russian PCB), but it just does not start.

Hello

Do you have a multimeter? If yes, what type / model?
Do you have a logic probe? If not, are you prepared to buy one, or make your own simple one (I can post up a schematic).

When you say “2732 ROM modification, the PCB already has some” do you mean that you think that the PCB track layout is designed for a 2732 EPROM, or do you mean that you have modified the PCB so that a 2732 EPROM should work?

Mark

If the board has the same track layout as an original ZX80 then the 2732 EPROM just requires a simple mod as per the picture, I have tried this and it does work.

Paul wrote: ↑Thu Nov 14, 2019 7:57 am Can you provide a link to the website of the producers?

It seems he does not sell ZX80 clone anymore and gone for Wilco PCB instead
But it was on his eBay store, here
https://www.ebay.co.uk/itm/PCB-DOUBLE-C ... 3175822007

No additional info was supplied, just an IC kit, no passives and PCB

Moggy wrote: ↑Thu Nov 14, 2019 12:33 pm If the board has the same track layout as an original ZX80 then the 2732 EPROM just requires a simple mod as per the picture, I have tried this and it does work.

I did some multimeter testing and concluded the PCB already modified to accommodate 2732 ROM.
But the fact that kit may come with empty ROM is very interesting

1024MAK wrote: ↑Thu Nov 14, 2019 11:39 am
Do you have a multimeter? If yes, what type / model?

Yes I do have Bort BMM-830-A
Hight precision digital one

1024MAK wrote: ↑Thu Nov 14, 2019 11:39 am Do you have a logic probe? If not, are you prepared to buy one, or make your own simple one (I can post up a schematic).

None at the moment, but yes, I am willing to do one, please send me a schematic

1024MAK wrote: ↑Thu Nov 14, 2019 11:39 am When you say “2732 ROM modification, the PCB already has some” do you mean that you think that the PCB track layout is designed for a 2732 EPROM, or do you mean that you have modified the PCB so that a 2732 EPROM should work?

I checked PCB with the multimeter and according to the schematic on Grants site that PCB already modified to accommodate 2732, no modification required

Thank you for your reply