Ms Pacman color issues

elekTRONarcade

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So, my Ms Pac board is working almost 100%, except the colors on the ghosts is screwed up. The ghosts are pink and yellow and they all have green eyes and yellow pupils. The maze colors appear to be fine. When eating a super pac pellet, they turn yellow instead of blue. I've searched around for the issue, and found two different similar issues here:

http://www.arcadegameover.com/pactrouble.html

First one:
Image58.jpg

Yellow maze. Yellow on top of midway logo. Pink monster is red, yellow is cyan. Green eyes yellow pupils.
Signal from 4A p11 to 3A,3B p11 low.
Signal from 3B p9 to 7F p11 is low

Second one:
Image71.jpg

M(Red, Pink, Red, Pink)
All monster eyes are blue with no pupil.
2B bad, removed, shorted p15 and 16, or p7 high.
Signal from 3A p7 to 2B p15 high.
Signal from 3D p8 & 3B p6 is low.

Neither is an exact match, but each have a bit of the problem.

I've replaced 3A, 3B, 4A, and 7F so far with no change. Unfortunately I don't have a logic probe or o-scope yet, so I can't actually check the signals, only replace components. I'm waiting on replacement chips for 2B and 3D to come in. I've also recapped the board, and the PS and filter boards are fine. Is there anything else I could check that might cause the issue?
 
Last edited:
Not without the logic probe...

You are stuck swapping chips. Wait till you swap the other two then come back. ;)
 
Usually if you have issues with the ghosts eyes its related to the 2125 ram 2A-2D. Try piggybacking them before desoldering and replacing. Alot of times you can pinpoint which chip it is like this.
If you havent already I would swap out color proms 4A and 7F with known good ones. Dont rule out their sockets, I have seen many pac boards with bad prom sockets.
 
Luckily I have two 16 pin sockets I can replace them with if need be. I had thoughts of piggybacking but wasnt sure if I could with RAM. Luckily I have a 16 pin IC clip just for that purpose lol.

So, it looks like I need to get on teh bandwagon and break down and buy both a good logic probe and an o-scope. Any recommendations for both cheap and good versions of each?

Hopefully Santa will bring me a Fluke as well :p
 
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