Sinclair ZX80 / ZX81 / Z88 Forums

They're the ones Lardo, not too vicious at removing gunk and especially good for cleaning ancient EPROM pins prior to programming them.

I have one of those. It gets bits of fibreglass everywhere. And it's itchy!

Thats the one! Works though.

msknight wrote: ↑Wed Jan 10, 2024 6:20 pm Poor 9v connection? We're talking the jack socket, or possible 7805 failure? How would I check this please?

Yes, both the jack socket contacts and maybe the solder joints. And for the 7805, the solder joints. For all soldered connections, a bright light and a good quality magnifying glass. But if there's any old flux (brown deposits) clean first with IPA or a specific PCB flux cleaning solution. For any suspect joints, desolder. Clean the component/connector pin and then re-solder.

For the contacts, apply some IPA or contact cleaner to the contacts. Re-tension them by pushing down with a flat bladed screwdriver (with nothing in the socket).

msknight wrote: ↑Wed Jan 10, 2024 7:59 pm I have one of those. It gets bits of fibreglass everywhere. And it's itchy!

Yes, the bits of fibreglass are annoying. Which is why I hold whatever I am cleaning over a bin.

The fibreglass "pencil' is good for cleaning chip legs/pins.

For the sockets, with the chip removed, again, examine under a bright light using a good quality magnifying glass. If you see any green, or any of the contacts look distorted or look different to other contacts, the entire socket should be replaced.

Otherwise, just clean each socket with a squirt from an aerosol can (using the plastic 'straw') of IPA or contact cleaner (but not the type that leaves an oil residue).

Mark

Moggy wrote: ↑Wed Jan 10, 2024 1:53 pm Forgot to add that Mostek chip pins tend to tarnish far more readily than other chips in my experience so the above may help the ROM at least which, judging by your picture of that board, the ROM pins look almost black or is that just bad lighting?

I went back and checked. They're getting on to the black side. Looks like that will be my first port of call once I've finished the new case for the first zeddy.

The black is likely silver that has tarnished.

From elsewhere on the web (not me this time ):

Way back in the day, when I used to repair computers for a living, some chips pins would turn black over time. If they were soldered in place this was not a problem. But back then, many computer boards used sockets. This would cause connection problems. The thing is only certain manufacturers chips would turn black. Usually TI chips were the worst. The thing is that TI used to (maybe still do?) silver plate their pins. The black build up was silver tarnish. Just like your mom's good silver. What we used to do was to take the chips and dip them in a silver cleaner, then dip them in rubbing alcohol, then in hot water. Then we would let them dry. The alcohol would remove any residue from teh silver cleaner. The water would remove the alcohol. The parts would come out nice and shiny and work for several years after that.

Mark

1024MAK wrote: ↑Wed Jan 10, 2024 9:58 pm The black is likely silver that has tarnish

Ah! Great. I'll de-socket the chip and take it to "Flog It." Should get a fiver at least.