Rommager
Member
I had an interesting problem on a revision A Centipede board. During the first 5 minutes or so that the game was on, it seemed to play fine, then slowly, the archer would begin to lose the ability to move left. Eventually, it would move only right, no matter which way you rolled the trackball. I ruled out the trackball, and so I knew the problem was on the logic board. Perhaps my troubleshooting will help someone else out. 
The revision A boards have a different circuit design for the trackball. I found the revision A schematics at arcade-museum.com.
1) I began by probing the the output of the IC at F10 (pin 6 for Horiz Direction), and would hear chatter when rolling the trackball. When the game started having the problem, I could hear the output was stuck low. I probed the input (pin 5) and could still hear chattering. I replaced F10 with a new socket and chip, but the problem remained.
2) I then cut out the IC at E11, and ran the game. Again, the output of F10 pin 6 died after 5 or so minutes, so I could rule out the E11 (along with any other part of the circuit). I replaced E11 with a new socket and chip.
3) I replaced the 3.3k resistors for trackball 1, R84, R86, R131, and R133 with 1/2 w 6.8k resistors. The problem was resolved! It only took replacing 2 chips before I figured out one of the resistors was apparently bad.
You may ask why I replaced the 3.3k resistors with 6.8k resistors. I found a tech note for Centipede at txtfiles.com (http://pdf.textfiles.com/manuals/ARCADE/A-J/Centipede [Trackball Tip] [English].pdf) which advised this modification for trackball issues. I have to say that the trackball is much more responsive than it was before (before the archer started moving only right), so I would definitely recommend this update for anyone who has a board with the 3.3k resistors. I imagine you might also have to replace R83, R85 R130, and R132 if you have a cocktail setup, as those resistors appear to be for the second trackball.
I also noticed my board has the intermittent fire problem mentioned in that tech note as well, so I will be replacing the 1k ohm resistors at R115, R117, R119, and R120 with 470 ohm resistors tonight. I am looking forward to playing a bit of Centipede tonight!
Anyhow, I haven't seen this issue in other repair logs before, so I hope this can help someone.
The revision A boards have a different circuit design for the trackball. I found the revision A schematics at arcade-museum.com.
1) I began by probing the the output of the IC at F10 (pin 6 for Horiz Direction), and would hear chatter when rolling the trackball. When the game started having the problem, I could hear the output was stuck low. I probed the input (pin 5) and could still hear chattering. I replaced F10 with a new socket and chip, but the problem remained.
2) I then cut out the IC at E11, and ran the game. Again, the output of F10 pin 6 died after 5 or so minutes, so I could rule out the E11 (along with any other part of the circuit). I replaced E11 with a new socket and chip.
3) I replaced the 3.3k resistors for trackball 1, R84, R86, R131, and R133 with 1/2 w 6.8k resistors. The problem was resolved! It only took replacing 2 chips before I figured out one of the resistors was apparently bad.
You may ask why I replaced the 3.3k resistors with 6.8k resistors. I found a tech note for Centipede at txtfiles.com (http://pdf.textfiles.com/manuals/ARCADE/A-J/Centipede [Trackball Tip] [English].pdf) which advised this modification for trackball issues. I have to say that the trackball is much more responsive than it was before (before the archer started moving only right), so I would definitely recommend this update for anyone who has a board with the 3.3k resistors. I imagine you might also have to replace R83, R85 R130, and R132 if you have a cocktail setup, as those resistors appear to be for the second trackball.
I also noticed my board has the intermittent fire problem mentioned in that tech note as well, so I will be replacing the 1k ohm resistors at R115, R117, R119, and R120 with 470 ohm resistors tonight. I am looking forward to playing a bit of Centipede tonight!
Anyhow, I haven't seen this issue in other repair logs before, so I hope this can help someone.
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