Re: Lisa I/O board troubleshooting, and schematic weirdness

On Mar 26, 8:25 am, Mr Ian Primus <ian_pri..._at_email.domain.hidden> wrote:

> I did not soak the boards - I did clean them with vinegar and a toothbrush, scrubbing the corrosion the best I could, then rinsed in alcohol. I did not actually submerse the boards in the vinegar though.
>
>   My Lisa 2/5s were horribly corroded and didn't
>
> > start
> > functioning until the boards were immersed overnight and
> > carefully
> > scrubbed.  I think there was green "crud" underneath
> > some of the
> > chips.
>
> That's a good point - there could still be junk underneath chips - what concentration vinegar did you use?

I used about 50/50 water and white vinegar. I disassembled everything (including lifting the motherboard off the tray) and soaked the three boards overnight. Even after the surface cleanings that preceeded it, there was a significant amount of chemical reaction - lots of bubbles. The four large bus connectors were completely green with crud beforehand. When I finished, all the contacts were gleaming. If you have a wall oven that can be set at ~140-150 degrees, that's a good way to dry them out.

One of the units had an open via, so that's definitely a possibility. It's tedious, but reasonably straightforward to check everything point to point. FYI: NOS wiring harnesses were available on eBay. I grabbed one for the worst of the two units. A bit of work to change out, but it solved a lot of intermittant problems.

Don't forget to check electrolytic caps! These things are old enough that some/all may be dried out.

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