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Did you follow the hints in the chapter about checking soldering points, jumpers and so on ?
Do you have a oscilloscope ?
Please try without NMI board first and ROM switch to 4 (ZX80) and 6 (ZX81).
And don't forget to put two jumpers on J96 when the NMI board is not present.
That's okay.poglad wrote:but I also found an additional SMD capacitor that didn't seem to have a home. I'll check again tonight.
As there is no value printed on, I decided to give one capacitor more than needed to check it's value (the amount of capacitors is different per value which will leave one as a free gift).
Please check all jumpers and the hints in the chapter. Important is R100 and J100 but there are more important things.
Please inspect your board first carefully for any unsoldered or bad soldered pins or eventually shorts.
Measuring the values with a multimeter, the video-related signals are nothing much like the ones in the guide - but I suppose that's because of the random video output I'm getting. I measured CLK on the Z80, and get 2.1V (not 1.8V) and on IC20 I get 1.46V (not 1.0V). Not sure if that's a clue.
Anyway - I had no idea that X1 had any particular orientation - I think I had it back to front. Tried to take it out and turn it round, but unfortunately its legs broke off. Well I live next to an electronics store, so hopefully can pick up another but it might not be for a day or two! Perhaps that's all it was!