Interesting Centipede repair

channelmanic

Well-known member

Donor 3 years: 2011-2013
Joined
Apr 5, 2008
Messages
17,110
Reaction score
1,093
Location
Texas
http://newlifegames.net/nlg/index.php?topic=65.msg122251#msg122251

This one looked like an Atari 2600 when you turned it on without a cart installed. It was an off white color with big red stripes on the screen.

There was no border vertically so that told me there was a problem in the synchronization circuitry - the circuits that generate all the different clock signals and the sync signals. The 74LS163 chips are similar to the 74LS161 that are in Pac Man and various other games. They divide a clock signal by varying amounts depending on how certain pins are set (high or low)... and if you check them with a scope or logic probe you'll see the different outputs. The outputs on M2 and P3 were stuck - dead. Replacing those gave me the game screen but it was full of garbage.

3 new RAMs later and the game is happily running.

When dealing with Centipede and you have bad RAM, don't order just one replacement. The RAM test stops when it finds a bad RAM. Replace it and run the test again, replacing any other bad RAMs until you get no more beeping when running the self tests.
 
Back
Top Bottom