TECH: Galaxian sync

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Archived from groups: rec.games.video.arcade.collecting (More info?)

Goodmorning to all,
I have a Galaxian board that will not sync. It is defiantly the board. I
have had other boards on my test set with no problems.what chip would you
look at? I will try to post a pic later if that might help...........Thanks
John

 

[Guest]

Archived from groups: rec.games.video.arcade.collecting (More info?)

That would be "chips" as any number of them could be bad that make up
the entire sync circuit. You NEED the schematic. Start at the sync
output on the PCB edge connector, and work your way back looking for a
weak or missing gate out (logic probe and DMM) and when you've run out
of possibilities, get a scope and start tracking the clock.

- Matt

 

[Guest]

Archived from groups: rec.games.video.arcade.collecting (More info?)

According to the schematics, the *CSYNC (negative-going composite sync)
signal is generated by a 7408 chip at location 6H, pin 6.

Coincidentally, just last week I worked on a Pac board with a similar
problem. It too had a bad 7408 chip. The output was reading a very leaky
100 or so ohms to ground. Replacing the chip cured the problem.

HTH,

Matt J. McCullar