Galaga Showing Garbage on Screen

SSilver2k2

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I picked up a semi dead galaga the other day. I tested the fuses, replaced them, checked the power supply and its at 5.2 (i checked the big cap thingie its at 5 - 5.2).

After its on for a while the monitor image gets short. If I turn it off then back on immediately it takes up the full screen again. Any thoughts on what is gong on. I have two galaga boards to swap and they both give garbage on the screen.

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Mine looked like that when I picked it up last week. The problem for me was that the edge connector needed cleaning. Someone had already put a switcher in it.

The picture shrinking sounds like it may be a monitor problem.
 
Picture shrinking is a monitor problem.

If the board isn't doing anything on power up then check for a dead CPU (closest one to the board edge), bad EPROMs (first 4 above that CPU), or dirty custom chip legs.

It can also be caused by bad sockets. I've worked on many Galaga boards that had socket problems. They used some VERY crappy sockets on those boards that end up with intermittent connection problems.

RJ
 
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