21 Jul
2004
21 Jul
'04
9:01 a.m.
One thing I
have found though - a *lot* of chips in this machine are
replacements, and the solder quality is total crud.
Ugh. Add "Solder
sucker", "Desolder wick" and "RoadRunner wiring pen" to the
"Tools Required" list too. I hope you've got a good soldering iron and a
powerful light (60W or so). All the RAM chips and both MC6821's are
replacements, and the sockets
for the LM1889 and MC6847 look to be non-original too, implying that
those suffered some form of destruction and were replaced. Given solder
quality, I'm going to check continuity on the address / data lines for
all the RAM chips and check for shorted tracks too.
Watch out - the tracks to the
RAM may be mixed up, i.e. A0 going to A8 and so
forth. Check the schematics, then buzz out the board with a continuity
tester. For some reason one of the RAM chips has a 220n
decoupling cap, whilst
the rest are 100n.
Shouldn't make much difference. If it looks like the 220n
is a replacement,
swap it for a 100n.