Sinclair ZX80 / ZX81 / Z88 Forums

I've just finished putting my second one together; I think I was lucky with the first as it worked first time and that gave me confidence to build a second.

The second is having a display issue and I have no idea where to start looking; it seems that the its "functioning" as PRINT "HELLO" causes the screen to display a slightly differently corrupted line at the top, CLS refreshes the screen back to the picture below etc. Sorry about the quality of the picture - it's a photo of a CRT, used specifically in case it was an issue with my LCD screens and has been used for both my other Minstrel and my composite modded '81.

I've checked the soldering with a magnifying glass - as far as I can tell all joints look good. The only "divergence" away from the standard kit was I socketed all the ICs rather than just the ROM/RAM and CPU and used the same make rolled-pin sockets as supplied in the kit.

Any clues?

Trev

Does it produce saving tones if you attach an audio amplifier to the mic output and you try to SAVE?

If yes, then the problem is limited to the part of the circuitry that generates the pixel data,

Mark

thanks Mark - I'll give it a try shortly.

After much faffing around involving laptops, supposedly amplified speakers, and eventually a good old fashioned cassette recorder, I can quite categorically state that there's no save tones. I tried a simple 10 PRINT "X", SAVE "X" - nothing.
I tried it a few times, just in case of typos (powered off and on between tries to make sure there was nothing in memory) and the screen stayed garbled and stable - no discernible save pattern. The issue I have is that if there was an error code, I couldn't see it - the screen being screwy really doesn't help.
I tried the same on my other Minstrel - and got the save pattern and tones on the cassette.

I have a very limited supply of diagnostic tools - essentially a multimeter and that's it.

Any advice on the next steps?

Trev

Now fixed.

'twas a pebcak (for those who know the acronym)

Jumper A13 in the wrong position.

Thanks TFW8B for the help

Trev

Good to hear that the problem is sorted

Mark

It always amazes me when something I've soldered together actually works...