Russian PCB ZX80 clone problem

Discussions about Sinclair ZX80 and ZX81 Hardware
crrush
Posts: 17
Joined: Fri Jul 26, 2019 10:38 pm

Re: Russian PCB ZX80 clone problem

Post by crrush » Tue Nov 19, 2019 10:21 pm

Erm wrote:
Sun Nov 17, 2019 6:22 pm
I'm following this more intently now.
Sure, I will inform you of my progress. However, let's deal with this situation technically wise. Let's also assume the ROM is okay now, but we have the very same picture.
The TV picture is generated only if the CPU (at least starts) reads ROM and may write to RAM, the later is somewhat being controlled by 8 bit IC5. Right? IC 20 is doing some clock job and address video signal, so it is rather good, its clock is ok (since CPU is working). Assuming that I may conclude that it is IC 21 to blame for the bad picture.
Also, IC 18 and 19 are responsible for synch generation. Also, IC 15 is mixing M1 cycles signal with synch, so it also falls into suspicion.
I am moving in right direction?

crrush
Posts: 17
Joined: Fri Jul 26, 2019 10:38 pm

Re: Russian PCB ZX80 clone problem

Post by crrush » Wed Dec 04, 2019 5:30 pm

Meanwhile, empty EPROM has just been confirmed

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