PacMan missing Pacman and Ghosts

HouBill

New member

Donor 2012
Joined
Mar 1, 2012
Messages
7
Reaction score
1
Location
Houston, Texas
I pulled a Pacman out of storage and it worked upon powering it up. It then lost all of the characters. Sound was there, and it sounded as if it were playing. Turning it off-on did not help. There is a lot of stuff on http://lawnmowerman.rotheblog.com but I do not find anything about the lost characters. Ideas for replacing an IC or is not that simple. Thanks.
 
From: http://www.arcadegameover.com/pactrouble.html

Caused by interfering or grounding databus RA0 thru RA5.

These can be found on 2A,2B,2C,2D p2,3,4,11,12,13, or 1E p11,12,13,14 or 2E p13,14.

2B p1 is high, or p2&3 or 3&4 or 4&5 shorted.

2A p12&13 or p11&12 shorted.

2E short pin7 to p10.

1E, 2E p15 shorted to p 11,12,13,14.

3D Bad or Removed.

3A, 3B p1 low.

3B p1 short to p8.

Signal 3E p6 to 3A,3B p1.

2F 10,13 low.
 
From: http://www.arcadegameover.com/pactrouble.html

Caused by interfering or grounding databus RA0 thru RA5.

These can be found on 2A,2B,2C,2D p2,3,4,11,12,13, or 1E p11,12,13,14 or 2E p13,14.

2B p1 is high, or p2&3 or 3&4 or 4&5 shorted.

2A p12&13 or p11&12 shorted.

2E short pin7 to p10.

1E, 2E p15 shorted to p 11,12,13,14.

3D Bad or Removed.

3A, 3B p1 low.

3B p1 short to p8.

Signal 3E p6 to 3A,3B p1.

2F 10,13 low.

This is where you need a logic probe

http://www.ebay.com/itm/LOGIC-PROBE...007?pt=LH_DefaultDomain_0&hash=item53eb0cb88f
 
2A-2D are rams that affect the colors of the ghosts. These rarely go bad.
The 7489 rams are fairly common to see bad and if its not those there are two ls283 and ls161 right below them that are also suspect. If I had this problem I would start at the 7489 rams. Usually you can piggyback these to see if it resolves the problem.
 
Pacman Ram

My 3H and 3F are 8225's. Are these the same as the 7489? And they can soldered over the existing IC's? What a deal. Bill
 
My 3H and 3F are 8225's. Are these the same as the 7489? And they can soldered over the existing IC's? What a deal. Bill

Your probably looking at the date code. No, I wouldnt solder it over the old chip but you can try piggybacking it to see if thats your problem. It doesnt work all the time, depends on the chip and how the chip failed. It usually does work on the 7489 rams.
You do have a midway pcb right?
 
Pacman Characters

It is a Midway pcb. The only other numbers of the IC's are 8120. I am not familiar with the term 'piggyback' in refernce to the IC's. How are they handled?
 
It is a Midway pcb. The only other numbers of the IC's are 8120. I am not familiar with the term 'piggyback' in refernce to the IC's. How are they handled?

This is a tech trick but you have to be really careful and have some way to see the video screen or have an assistant. It is just like it sounds, you piggy back good ram chip right on the suspect ram chip and when garbage clears up, you found the bad chip.

EDIT:
Copied this from a search and cut it down to this and explains method much better.

The piggyback method requires that you install the test chip
over a board RAM chip so all pins make good contact and no pins
short together. The test chip must be oriented correctly as well.
There is a notch or dot (or both) on one end of those ICs. Those
markings must line up because if the test chip is installed
backwards, it will likely be damaged when power is applied. You
can press the test chip pins against a tabletop to push all pins
inward slightly, and that will provide some spring tension when
the test chip is inserted over the board chip and can hold it in
place. It's OK if you want to hold the chip with your fingers and
then power up the computer. There is only five volts present and
therefore absolutely no danger of electrical shock. Again, if the
bytes free number changes, that board IC is probably bad and
should be changed. If there is no change when all RAM is checked,
suspect the two RAM control logic ICs mentioned above. They must
be replaced to diagnose a problem there.

here is the page this came from

http://personalpages.tds.net/~rcarlsen/cbm/memory.txt
 
PacMan

Well, that piggy-back is all new to me. I have double-checked 3F and 3H and also 2K. The numbers are N82S25N 8103. It is a Midway board. I will be ordering a couple of the RAMS. It will be a week before I can get back to the game.
 
I'm planning to pick up a board shortly that has this same issue, and I've read a lot of possibilities for what could be causing it. The only reference on Lawnmowerman's page is a bad V-RAM Addresser, which he indicates is a "rare case".

Please do check back in if and when you get the problem fixed, or even with what you try that doesn't work.
 
I'm planning to pick up a board shortly that has this same issue, and I've read a lot of possibilities for what could be causing it. The only reference on Lawnmowerman's page is a bad V-RAM Addresser, which he indicates is a "rare case".

Please do check back in if and when you get the problem fixed, or even with what you try that doesn't work.

+1

Maybe it will put a fire under my @$$ and start on my Super Pac-man. I am working on the Operation Wolf sound boards right now and just don't want to start another project. I also want the re new kit for this board as it has them crappy resistor packs before I start to trouble shoot it.
 
Hey Quattrohead

Where did you get your replacement 74LS75 from? My board is doing the same thing, and that chip looks like the easiest to replace. So figured I would start there.
 
I got mine off an old board I had kicking around, a phone PBX to be exact. Every chip was socketed, so it was easy to pull them.
Also anyone trying the piggyback test should note that will only work if the chip gate has failed open, if its failed short you won't see any difference with this test method.
I found my bad gate by measuring and comparing the resistance of the same gates on different pins of the chip. One was noticeably different.
 
Back
Top Bottom