Odd Keyboard Issues

[RWAP]

Someone has sent me their ZX81 - a new membrane has been fitted and the ZX81 works perfectly for a few seconds, but then the keys 2 W S and X stop working...

Any ideas - I have re-soldered the pins on the keyboard connector - one appeared a little loose and this made it slightly better (ie. they worked when you turned the machine on).

Could it be the ROM?

[Moggy]

Hi Rich

I have sent pm with possible solution

Regards Moggy

[sirmorris]

Hmm, the matrix has 2, W, S and Z all on bit 1 with 9 O L and '.'

Are those keys affected too?

[RWAP]

Oddly the 9 keys etc were initially affected before I resoldered the keyboard connector, but now they seem to work (will have to retest). That is what makes me think that something else is happening rather than just the connection to the keyboard. Again, the odd thing is that they all work when I switch on the machine - I can test every key working across left to right and down, until I get to S and by then, 2 and W have stopped working.

I have also tried the keyboard top in my own ZX81 and it works fine.

Moggy has suggested the ULA - the chips on this one are socketed, so it must be a self-build. I have tried swapping the Z80 and ROM from a TS1000 I have here, and it has no effect.

Alas I do not have a socketed ULA to try!

Hmm - it certainly is an odd one. Alas my own ZX81 produces a very dark grey output on my TV and I cannot read the screen easily - whereas this one does produce a very crisp white steady picture - the best I have ever seen from a ZX81, so I don't want to simply swap the motherboard!

[RWAP]

I have still not managed to rectify this issue - does anyone have a socketed ULA I could try?