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Old 21st Feb 2021, 8:45 pm   #612
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,339
Default Re: Non-working Commodore PET 3016

Originally Posted by julie_m View Post
anything's going to look a bit disappointing after that absolute money shot of the fault on the address buffers!
Not to mention a definitely duff UD7 PROM as well.

It's looking like this one is going to be a slow uphill slog. The potential damage from damp is what concerns me most, there could be one or more open circuit / corroded VIAs. The oxidisation on the pins of the PROMs was really quite severe, if every tinned surface and solder joint on the PCB is like that then Colin has done very well to remove the devices he has so far replaced with relatively small damage.

Among other things, I work on door entry access panels which are usually mounted on outside walls - if the rain seals get damaged or the panel isn't sealed up tight enough and the board gets wet, stays wet for a while and then dries the solder can turn into something which behaves almost entirely unlike solder, no amount of heat from an iron will melt it unless you carefully scratch through the dull grey surface with a fine point to make it all shiny again. That takes a lot of time and patience.

For the time being I think we have to focus on trying to get the CPU to keep running when all its pins are connected to the databus - if we can achieve that and that gives us video and sync signals then we are in with a chance.
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