Baby Pac-man MPU solid green light

ssRat5

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Hello all,

I just got my very first arcade machine, a non-working Baby Pac-man. So far the best I can tell is the monitor comes to a white screen and the MPU is stuck a green light. (Not sure if the issues are related)

I figured I would start with the MPU and I have been trying to follow the guide (http://forums.arcade-museum.com/showthread.php?t=243363) regarding this to the best of my novice abilities and here is where I am at.

1. Checked the test points on the MPU and they check out except for TP3 which is much lower, I assume that the Baby pac is lower than other MPUs? (I think I saw that somewhere)

2. Checked pin 40 on U9 at power up, checked out ok.

3. Checked U9 pins, 3, 5, 36, 40, checked out ok I think, pin 5 was about 2.2 I think, not sure if that is good enough.

I haven't pulled and reseated the ICs yet, I ordered a puller because I was nervous using a screw driver. The battery was replaced at some point but looks ok to me. Is my next step replacing U6, U9, U11 ? If so and suggestions where to order from or should I try to get the equipment to do it myself?

Thank you for any suggestions you have and for making this a great forum!

Michael
 
I'd pull and reseat those chips like you said, but the problem is probably down near that battery in the reset section. The thing about pin 40 that you checked is that it needs to go from low to high, if it doesn't do it in the right little window of time, the board never starts up.

Usually though those chips are all filthy, so if they're not making good contact in their sockets, the board will never start to boot anyways becuase it can't read the code or access the pia/cpu chips.
 
Thanks! So pulling the chips is definitely the next step. I don't have a logic probe but using my multimeter I checked pin 40 on power on and it went from 0 to around 5 volts pretty quick. No idea if in the correct window though. When I pull the chips should I clean them? What should I clean them with?
 
OK. I pulled and reseated the chips, they looked good for the most part except U6 was a little dirty, I used some contact cleaner on it. Still solid green.

Doubled checked the test points as follows:
TP1 4.95
TP2 15.22
TP3 4.64
TP5 5.00
TP6 0.259

Not sure where to go from here.... :-(

Is a good step to get replacement ICs to plug into the board?
 
Check the lower portion of the board where the battery is/was and look for acid damage. The reset circuit that was mentioned is one of the things that gets damaged when the battery leaks. If it were mine I would pull all sockets and check under them then install new dual wipe sockets, fixing any corroded traces if needed. I have seen some that appear to have no acid damage but then found bad traces under the sockets because the acid sits there and eats them away. I have also seen the pins corrode in half under the socket, again with no visible acid damage on top. I wouldnt even bother troubleshooting an mpu board until the sockets have been replaced and all traces inspected very carefully.
 
Pull the MPU and take it to the bench. Power it from the bench, and see what you get. Remove the 5101 & the 6801 & the 6821 PIA in the middle (U10?) and power it up.

If the LED is still lit solid, you most likely have a acid corrosion problem. Rebuild the reset section and replace the crappy single wipe sockets with fresh new dual wipe sockets.

If the LED is still lit solid, replace the ROMs at U2 & U6. (replace their sockets if you have not already done so)

It is also helpful to have a known good set of 68's on hand. 1 - 6800 CPU, 2 - 6821 PIA's, 1 - 6801 RAM, 1 - 5101 RAM (Bob Roberts sells these in a set)
 
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