Pac Man board repair help needed

smalltownguy2

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Received a non-working Pac board from a fellow KLOVer. Here's what it does:

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Changed out the eproms from a known working board, as well as the vram addresser and z80. Board acts the same way regardless.

I don't see this image on any of the common pac repair logs / pages.

Anyone see this before? Where do I start?
 

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Make sure the regulators in the 5VDC line hasn't failed.

Edward

+1

and take; no report the voltages also. I do NOT want to see they are fine, I want to see the voltages you measured. The +5 and any other voltages the board takes. I bet something is pulling down the voltage.
 
+1

and take; no report the voltages also. I do NOT want to see they are fine, I want to see the voltages you measured. The +5 and any other voltages the board takes. I bet something is pulling down the voltage.

Coming back to this now. How do I take these measurements?
 
Upon closer inspection, it appears that the 2125 ram in row 2 (2A-2D) are looking pretty cruddy. I'm going to swap out those ram chips with replacements and we'll see how that works.

Riptor...PM incoming :D
 
I highly doubt the 2125 are going to help that problem. Those rams affect the colors of the characters.

Thanks for chiming in, Riptor. Any ideas on what's causing this? I metered C2 and C3, both have 5v on them. I'd like to use a logic probe on this board to start looking at chips. Where do I hook up the red and black leads?
 
Not sure never seen that one, don't want to throw guesses out there. Do you have some known good color proms to swap out?
Hook up your probe to cap C3. Negative towards the edge of the board.
 
Not sure never seen that one, don't want to throw guesses out there. Do you have some known good color proms to swap out?
Hook up your probe to cap C3. Negative towards the edge of the board.

I do have some good color proms. I'll get those swapped in and start probing the board.

Thanks - will report back. I appreciate it.
 
If you can read the high score and the credit with fruit at the bottom but not the maze then check the 2125(93415) at position 2A and 2B also check for a bad 74ls158(quad 2 input multiplexer) at 3A.
 
Swapped in good color proms at 4A and 7F. Both tested bad.

Progress!

With new color proms, here's what I have now:

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Everything I've read about this type of situation points to issues with the chips in row 2.

Like Darthi8nt mentioned, I have to may have to check/replace the 2125's in row 2.
 

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I just checked the repair log info on Lawnmowerman's page, where it states:

HI Score & Credits legible, no Maze or graphics. Shorting 3E pin 6 to pin 7 shows maze but no sprites.

Bad 93415 RAM pulling Chips Select down.


I probed 3E pins 6 and 7, and indeed, the maze did appear. So that confirms it, I have bad ram in row 2. Since they all look shitty, I'll probably change them all.

Riptor can get me the ram, but this board is missing the heat sinks too. Anyone know where I can find those?

Also, side note - could the missing heat sinks have contributed to the demise of these ram chips?
 
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