Sinclair ZX80 / ZX81 / Z88 Forums

Thanks, think so and leant a lot a long the way, and thanks for help.

Just need to get the keyboard fixed and then get some games loaded

Composite mod solved the picture quality from the RF modulator.

Sound was a failed D9, replaced and now beeping.

Unfortunately keyboard membrane fell apart after cleaning the keys, so new one on order.

Getting there slowly.
New DRAMs installed and up and running. Upper memory passed

Keyboard works.

TV RF Output a bit iffy, could be modulator.

No sound, so that needs looking at.

Interesting how the short on the DRAMs did not really show itself until I fixed the power rails. Mark was correct and the resistance measurements across the power rails may not show the fault. My guess so far is the 7805 regulator went first, this then killed TR4 and the loss of the power rails kill...

Thanks, interesting how far out the readings are and I now understand why it is recommended to change the electrolytic capacitors. I still have a few to change and I have a some 4116 DRAMs on order. Probably can't get a replacement ULA until April. Need to look at the screen output. Is this an artif...

Getting somewhere now swapped ULA 6C001E-7 with an earlier 5C112E-3 and it's up and running the Diagnostics but tv out signal is a bit rubbish.

Well not much is running X1 is dead but X2 is alive a least. This could be a long process.

OK voltage and current ok with the ULA back in but diagnostic ROM is not running.

Time to get the scope out and see what is alive.

So, I was lucky. IC13 removed still same, IC12 removed and now I have stable voltages and all correct.

Will Plug ULA back in a see what happens.