Testing Galagas

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I've been having some fun servicing a pile of Galaga boards and have found
a few commonalities that I thought I'd share:

*The custom chips legs are corroding off - spray contact cleaner on them to
slow this down, something that leaves a fine silicon film might be best.
*White IC sockets are trash - replace them
*Ceramic SIP resistors are trash - replace all of them!
*Weird problems are sometimes traceable by momentarily shorting circuits to
ground on the video board that use resistor pull-ups, the control ICs do
not have strong pull-ups (otherwise they would not need the resistors) and
you can learn a lot of how the images are built this way. Interesting
watching lines appear, characters vanish, stars scroll sideways....
*The horizontal delay timing is CRITICAL and if you are getting RAM errors
but the RAM is good, then check the 220pf cap on the delay circuit...

That's all for today. But I did get in my Z80QT pod and boy that one is
FAST on the RAM tests! A couple of seconds to verify a 1k block instead of
a minute or two (short test). What a difference to troubleshooting time!

John :-#)#

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Received on Sat Jun 15 23:02:45 2002