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Repair Log - Pac-Man

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Anonymous
April 26, 2005 4:40:43 AM

Archived from groups: rec.games.video.arcade.collecting (More info?)

Pac-Man PCB Repair Log:
-----------------------

Symptom: Game isn't syncing correctly and some strange characters are
being displayed (can't tell what they are).

Solution: Put the PCB on my test bench and confirmed there was little
or no video sync. Normally, this is either 8C (74LS74), 2S
(74LS161) or 2R (74LS161). Socketed and replaced 2S and
the game picture was stable.


Symptom: Screen is full of "T"s, except for some random characters in
the upper left corner.

Solution: Pressed on all of the PROMs and the RAM (4R popped - RAM).


Symptom: Game displays full screen of garbage. Several reboots
confirms the garbage is consistent, so the game is trying to
boot.

Solution: Replaced all of the RAM (4K, 4L, 4M, 4N, 4P & 4R), since my
gut told me something was wrong with the RAM.


Symptom: Game displays a blank screen.

Solution: Suspect this is a problem with the ROW 6 PROMs, so I
install my bootleg aux PCB (has Z80 and ROW 6 PROMs on it,
so it bypasses the on-board ROW 6).


Symptom: Game boots to the grid pattern screen, but just keeps
rebooting. The test screen information can also be seen in
the background (3 Pac-Man, 1 COIN is 1 Credit, etc.).

Solution: I now know something is wrong with the ROW 6 PROMs, but I
focus on the resetting problem. Install the ABC Diagnostics
aux PCB and run the tests against the game. It boots,
works fine and confirms everything on the PCB (it can't
test the ROW 6 PROMs) works fine except for the watchdog
(74LS161 at 9C). Piggy-backed a good IC on the watchdog IC
and the watchdog started working. Socketed and replaced
the watchdog (tested and works fine). A logic probe should
have also shown problems, but the piggy-back was quicker. :) 


Symptom: Removed the ABC kit and the game only shows a blank screen
again (using the on-board ROW 6 PROMs).

Solution: Installed the bootleg aux PCB and the game boots and plays
fine. Replaced PROMs 6E and 6F and the game now boots
normally using the on-board ROW 6. Done!

More about : repair log pac man

Anonymous
April 26, 2005 4:40:44 AM

Archived from groups: rec.games.video.arcade.collecting (More info?)

Nice info.

-r-

"Scott Caldwell" <lscottcaldwell@excite.com> wrote in message
news:f6gbe.325$gd5.146@newssvr12.news.prodigy.com...
> Pac-Man PCB Repair Log:
> -----------------------
>
> Symptom: Game isn't syncing correctly and some strange characters are
> being displayed (can't tell what they are).
>
> Solution: Put the PCB on my test bench and confirmed there was little
> or no video sync. Normally, this is either 8C (74LS74), 2S
> (74LS161) or 2R (74LS161). Socketed and replaced 2S and
> the game picture was stable.
>
>
> Symptom: Screen is full of "T"s, except for some random characters in
> the upper left corner.
>
> Solution: Pressed on all of the PROMs and the RAM (4R popped - RAM).
>
>
> Symptom: Game displays full screen of garbage. Several reboots
> confirms the garbage is consistent, so the game is trying to
> boot.
>
> Solution: Replaced all of the RAM (4K, 4L, 4M, 4N, 4P & 4R), since my
> gut told me something was wrong with the RAM.
>
>
> Symptom: Game displays a blank screen.
>
> Solution: Suspect this is a problem with the ROW 6 PROMs, so I
> install my bootleg aux PCB (has Z80 and ROW 6 PROMs on it,
> so it bypasses the on-board ROW 6).
>
>
> Symptom: Game boots to the grid pattern screen, but just keeps
> rebooting. The test screen information can also be seen in
> the background (3 Pac-Man, 1 COIN is 1 Credit, etc.).
>
> Solution: I now know something is wrong with the ROW 6 PROMs, but I
> focus on the resetting problem. Install the ABC Diagnostics
> aux PCB and run the tests against the game. It boots,
> works fine and confirms everything on the PCB (it can't
> test the ROW 6 PROMs) works fine except for the watchdog
> (74LS161 at 9C). Piggy-backed a good IC on the watchdog IC
> and the watchdog started working. Socketed and replaced
> the watchdog (tested and works fine). A logic probe should
> have also shown problems, but the piggy-back was quicker. :) 
>
>
> Symptom: Removed the ABC kit and the game only shows a blank screen
> again (using the on-board ROW 6 PROMs).
>
> Solution: Installed the bootleg aux PCB and the game boots and plays
> fine. Replaced PROMs 6E and 6F and the game now boots
> normally using the on-board ROW 6. Done!
!