Sinclair ZX80 / ZX81 / Z88 Forums

ESR tables, a useful guide to the readings from your component tester;

https://quantumwarp.com/kb/articles/44- ... -esr-chart

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 artifact of running and Issue 2 board ULA in an issue 6a board?

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 killed 2 DRAMs.

The over voltage on the 7805 may have also killed the ULA. Z80 survived have not tested to the ROM yet and not sure yet about the ZX8401 although it must be working to a degree but not sure what is causing the display issue when running the diagnostic ROM.

Couple of lessons so far.

1. Use a bench power supply from the start
2. Measure input voltages.

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.

Sound was a failed D9, replaced and now beeping.

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

Composite mod solved the picture quality from the RF modulator.

Sounds (!) like you are nearly there with a working machine. Well done

Mark

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