Problems with my ZX81s

[walterg74]

As said, the bit of the red solder mask that has come off is not a problem electrically, it is jus cosmetic.

With the green issue 1 board, have you tried cleaning the edge-connector contacts with an eraser? The type that is suitable for ink pens. Or a PCB cleaning block.

Mark

Hi Mark,

I tried cleaning it with alcohol, but there seems to bemetal missing from it, not just dirty. I think it shows in the first of its pics.

[1024MAK]

It's hard to see on on the pictures. The contacts are made from copper tracks which have been coated in a tin/lead coating similar to solder.
Alcohol will only remove some contamination. It will not remove all contamination.

It is possible for edge connector contacts to wear through, normally after the tin/lead coating has worn through you can see the harder copper underneath. If this wears through, you would be able to see the fibreglass PCB material. It is not possible to say how common worn out edge-connector contacts are, but I don't remember very many members posting about it.

It's certainly worth a try with a slightly abrasive cleaner.

Mark

[gammaray]

Alcohol should not be used as it dissolves any aluminized electrical connections like the keyboard ribbon.

[RetroTechie]

For the edge connector, try using clean paper (no ink, fingerprints or 'glossy' layer etc). This acts as a very fine / very mild sandpaper. With no solvent of any kind. Regular printer paper works well.

At first you'll see the paper catch black dirt, simply continue with another piece of clean paper. After a bit of rubbing you'll see the tinned contacts start to shine again. Well somewhat anyway..

RAM pack etc. might need a few insert / remove cycles after that. But usually this procedure works well for me with tin-plated connectors. Note that connector-dirt may have stuck on the peripherals' connector as well. So try cleaning those connectors too if necessary.

[walterg74]

Thanks all, I'lll give it a try, even if it's just to have a replacement board, since without being able to get a working ULA, it's just the same anyway, as I have 2 machines but only one working UlA