On Tue, 27 Dec 2011 22:13:31 +0000,
(D.M. Procida) wrote:

My Christmas present to the children was a Commodore 64.

I picked it up a couple of months ago, and ran it for several hours to
test it; it was all fine.

On Christmas Eve I tested it again; after a few minutes it would start
throwing junk all over the display and then lock up, and I realised that
the difference was the house at room temperature where it crashed, and
the much cooler garage where it wouldn't.

We've repaired it now (mostly), by resoldering many of the pins on the
PCB where the solder seemed to have developed holes. I've never noticed
this phenomenon before, even in much older equipment. I assume that it
wasn't like that after manufacture.

What causes it?

Presumably, a 30-year-old computer would have had proper lead solder,
not this tin-whiskery lead-free stuff.

Actually it can't have been the soldering alone that fixed it because it
continued to crash; I also used a hot air gun to try to identify the
component that was failing after warming - I only once managed to get
that to trigger the fault, but since then, it hasn't crashed again.

So the crashing is fixed, but the next thing to tackle is the sound
output, which is barely audible.

Anyway, the children have been happily playing The Hobbit and Attack of
the Mutant Camels from tapes that have been sitting in boxes for nearly
three decades, which isn't bad going.

Daniele


Fault finding is probably better assisted by a can of Freezer Spray
from the local Maplins or equivalent.

The solder rot is probably extant because the OEM used solder with a
highly active or acid flux and lousy cleaning (if the board was
cleaned at all) to overcome oxidation of plating on cheap and nasty
PCBs and the terminations of cheap and nasty components to increase
the yield but at the expense of medium to long term reliability. (I
opened up a Sinclair ZX Spectrum once, it looked like a rat had
cr@pped the solder onto the board.)

Reflow the joints with some good honest 60/40 Lead based solder (still
legal for repairs) and a decent temperature controlled soldering iron.
Clean the reflowed joints with Isopropyl Alcohol - if you can get hold
of it - and a stiff brush followed by de-ionised water. Ensure the
board is completely dry before re-applying power.

Regards
JonH

p.s. If you look diligently on the web, you should be able to find US
military handbook MIL-HDBK-2000 (Previously MIL-STD-2000 and WS-6536)
which goes into much more detail and is in the public domain. It's
successors, the IPC 6100 series of workmanship standards are ruinously
expensive.