pac-man stuck in self-test mode

Superully

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hi guys, i thought i had figured this out, but i was wrong :(

it all started with this thread: http://forums.arcade-museum.com/showthread.php?t=91912

let me sum things up, i don't want you to have to read all this again:
- my pac-man was stuck in self-test mode once i powered it up (see pic 1)
- got a lot of different suggestions like replacing the fuse holders, reseating the chips
- tested the board in a friend's working pac cab -> same result: stuck in test mode
- found two "blown" capacitors on the board (see pic 2), replaced them
- finally got the chance to test the board in my cab (after finishing the restoration)

RESULT: STILL STUCK IN TEST MODE

my conclusion: since the board is producing the same error in a friend's cab, the error DEFINITELY has to lie with the pcb itself!

do you have any suggestions for me?
 

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Does that screen change or flash...anything?

Thats not self test. Check and make sure DIP SW 8 is off :)

Whats up with that diode thats tied to the GU1C? Thats not supposed to be there.
 
Does that screen change or flash...anything?

it changes between four different screens (didn't want to bore you with all four, but since you've asked --> see attachments)

Thats not self test. Check and make sure DIP SW 8 is off :)

in the other thread someone suggested this was self-test mode. both DIP SW 7 & 8 are OFF
 

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Whats up with that diode thats tied to the GU1C? Thats not supposed to be there.

are you talking about the setup as shown in the attached picture? because this is how it looked originally when i got the game and that's why i soldered it back on the same way. no idea what the function of it is supposed to be ...

any ideas?
 

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Well that certainly is different. My boards don't look like that at all. Can you take a close up of the whole board? Looks like yours might be hacked up a bit. I wonder what else is not like it should be...
 
Here is a snap of mine...
 

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Can you take a close up of the whole board? Looks like yours might be hacked up a bit. I wonder what else is not like it should be...

i've had the attached picture (pic 1) on my computer, if it's not good enough i can take a better one. note that my pac-man also came with a credit board (pic 2). for a better quality, here are the flickr links:

main pcb: http://farm2.static.flickr.com/1283/4695781791_06bb46ba59_b.jpg

credit board: http://farm5.static.flickr.com/4035/4695780201_6011648c44_b.jpg
 

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Thats an interesting hack, never seen that one. Looks like they slapped in a 7805 regulator.

The credit board was used on export machines only as far as I know. I have yet to come across one.
 
what's that and where's that? ;)

Its the transistor in front of the two large caps. That should be a 4 pin transistors marked 78GU1C. Someone has hacked in a 7805 regulator in its place.


You have custom sync bus and vram chips. The legs are probably dirty or broken. Carefully remove the one next to the Z80 and clean it.
 
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Its the transistor in front of the two large caps. That should be a 4 pin transistors marked 78GU1C. Someone has hacked in a 7805 regulator in its place.

ah, now i see it! what's the use of that hack?

You have custom sync bus and vram chips. The legs are probably dirty or broken. Carefully remove the one next to the Z80 and clean it.

are you talking about the two chips circled in red on the picture? i already cleaned / reseated them the last time - they looked totally fine to me, but i can do it again!
 

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Yes, those are the customs. The early pac boards used customs then they went to a daughterboard with TTL chips. If you already cleaned them and made sure there were no broken pins then they should be ok.
Measure you 5vdc across capacitor C3 and see what you have. That hack was done because the original IC used there is rather expensive and hard to find. See what your 5v is on the board and we will go from there.
I noticed your 2114 rams are not socketed. Thats pretty rare but I have seen a couple boards like that before.
 
test switch? isn't it already in test mode?



where can i increase the +5v?

It is not in test mode....It's not fully booting up and hanging at various points of it's boot up sequence.

To increase the 5VDC line....I'd start by undoing that hack....it's part of the 5VDC circuit.

Edward
 
No its not in test mode. Its going through self-test and then looping when trying to boot the program. Could be from the low voltage, bad ram or something in row 6(eproms, sync bus custom, sockets, Z80). There are other possibilities but those are the most common culprits.
The voltage is not adjustable. Im sure your low voltage is caused by that hack but its possible a bad IC could be pulling it down too.
 
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so what's there to do? replace the 7805 regulator with a 4 pin transistor 78GU1C? or anything else?

Yeah that would be a good starting point. You could jumper 5 & 12v to the board from a switcher for testing purposes(make sure you pull the 4 fuses first).
 
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