Pacman Repair Logs
Symptom: Garbage on screen. Screen is flipped. No audio.
Board had squished looking blobs for ghosts, text, and fruit. The maze looked as if it were Atari 2600 quality. Very blocky.
Replaced a 74LS174 at 1H to fix the garbage graphics. Pin 9 on it was dead. Replaced 74LS259 at 8K to fix the flipped screen problem. This chip also controls the 74LS273 at 2M for audio but now the speaker would output garbage noise. Replaced the 74S89 RAM IC at 2L to fix the sound problem.
Symptom: Garbage on screen. Dead.
4 ROMs failed checksum. Burned new EPROMs for 5E, 5F, 6H, and 6J and tested the board.
Symptom: Dead, Garbage on screen.
Fixed a bent pin on ROM 6F. Roms at 6E, 6H, 5E, and 5F were bad. Programmed new ROMs and tested board.
Symptom: Colors wrong on maze
The PROMs at 7F and 4A were for a Pac Man Plus and not a Pac Man. Burned new PROMs and tested board.
Symptom: Maze would disappear and ghosts would all be blue.
This one took awhile to track down. The maze would be there then disappear. Then it would be fuzzily fading out from top to bottom. Very odd symptoms. When the maze disappeared the ghosts would all be dark blue in color and the text describing their names would be the same shade of blue.
Found pin 1 on 5B / 5C, pin 3 & 5 on 5A, and pin 1 on 4D were floating. These pins are tied to +5v through a 1k ohm resistor. Replaced the 74LS194 at location 5C to fix the board. This chip was pulling too much current on pin 1.
Symptom: Sparkling garbage in text and maze
The high speed RAM is used for moving graphics, not the maze. Since the moving characters were perfect the RAM was good. Traced it back to the character EPROM at 5E. EPROM tested good in a programmer but would not run at speed. Replaced the EPROM to fix the game.
Symptom: Garbage on screen.
This was another board that had squished looking blobs for ghosts, text, and fruit as if it were Atari 2600 quality. Very blocky.
Checked the 74LS174 at 1H and it was stuck low. The chip was constanly in clear mode. Checked the circuit and found multple chips hooked to that line, labeled "P" on the schematic. Replaced the 74LS107 IC driving that line and played the game.
Tip: Burning new PROMs
When burning PROMs for this game, there are some chips that CAN be successfully substitued.
The 82S126 at 1M and 3M CAN be replaced by an 86S129 PROM.
The 82S126 is Open Collector outputs and the 129 is Tri-State.
I have not tried subbing out the 129 for the 126 at location 4A.
The 82S123 at location 7F is the video output PROM. It CANNOT be replaced by the 82S23. It will technically work but does not have enough current drive and the output is very low resulting in a VERY dim display on the monitor.
Symptom: Dead. Horizontal lines through playfield, but not scores or level/men remaining area.
Replaced 3 ROMS with corroded off legs to fix the dead board problem. The lines looked like a failure in the high speed video memory. Every chip I checked the Data Out line with the logic probe resulted in the signal going nuts on the probe AND on the screen. The well calibrated finger to the bottom of each chip made the screen go nuts. Checked the Data In lines and they were OK. The Data Out connections went from the RAM chips to the 74LS75 IC at location 3D and were tied high by RM2. Touching either of these made the display go nuts.
Checked RM2 (5 pin SIP resistor network. 4 1k resistors with a common to pin 1) which was to tie the DO lines high. There was no connection between each resistor and pin 1. Replaced RM2 with one from a parts board to fix the video.
Symptom: Blocky graphics
Pac Man would coin up and play, but the grapics on the screen were nothing but large squares & blocks.
Replaced EPROMs at 5E and 5F.
Symptom: Flickering garbage graphics. Game will not play blind
The VRAM Addresser (284) module was not in the socket correctly. Removed module and discovered that 2 pins were missing from the bottom. Replaced the socket on the bottom of the module, reinstalled it, and played a few games.
Model: Pac Man 11-in-1 Symptom: Dead. Burned power connector
Replaced the 4 power traces on the connector with copper circuit tape. Board would power up but was dead. The CPU and EPROM board added on as part of the 11-in-1 mod had bent pins on the bottom socket. Replaced the socket and played a few games to test the board.
Symptom: Dead. Burnt edge connector. Black screen.
Repaired the burnt edge connector with copper circuit tape. Powered up the board to find it was dead.
Checked the reset line on the CPU. It was stuck high. Checked pin 9 of IC 9C and found the reset switch was working properly. The IC at 9C was not receiving the VBLANK signal on pin 2. Traced this back to the 74LS74 at 5M. Found the 16V, 32V, 64V and 128V clocks were missing. Further troubleshooting revealed that all of the V clock signals were missing.
Checked the IC at 3N and found the 16H and 64H signals were present on pins 11 and 12. Replaced the IC, no change. If pins 11 and 12 are shorted together, the game will boot but will have the screen divided into 9 identical small screens. checked the 74LS161 ICs at 3R and 3S. The IC at 3R had identical outputs on pins 11, 12, and 13 instead of divided clock signals. Replaced the IC at 3R and played a few games to test.
Board had attempted repairs already done.
There were a few pins on the machine pin sockets from the attempted repairs that weren't fully soldered in. Once that was done the symptoms looked like bad RAM. If the board was flexed it would give different bad RAM symptoms - All zeros, colored text/graphics, and even booted once.
Broke out the pscilloscope on this one... the upper data bits were horribly garbled. Replaced the 6 2114 SRAM sockets and tested. Board died during extended testing. The Reset* line died. Without the proper reset pulse at power on the Z80A CPU will never start.
Replaced a 74LS161 at location 9C to fix the reset circuit.
Symptom: Garbled sound.
This board had been worked on before. There were many patches on this board and the IC at 1N had many traces and pads pulled. It also had many of its holes DRILLED out.
Removed a short between pin 5 and 11 on the 7489 RAM at 2L to fix a portion of the sound.
Removed short between pin 8 of 1N and R4. Patched open trace between pin 9 of 1N and R4. Now the sound disappeared. This was because one of the inputs on the digital switch was shorted directly to the resistor on the output.
Patched open trace between pin 7 of 1N and ground. Noticed that 1N was incorrect. Replaced the 4006 at 1N with a proper 4066 IC and redid many patches on the board then played a few games to test the board.
Symptom: Random reboots
Cleaned the Z80 Sync Bus controller chip's pins. This was the old custom chip version with tarnished legs, and not the daughterboard. Replaced the bad CPU socket and ROM 5E sockets to finish the repair.
Symptom: Dead hacked board.
Board was poorly hacked and had jumper wires that were not soldered on one end.
Removed the 8 EPROMs for the Ms Pac Man bootleg hack, removed several jumper wires, fixed 5 cut traces, and installed freshly programmed Pac Man ROMs in rows 5 and 6. Tested game.
Board was part of a group of 7 boards sent in for repair. It would not try to boot and was stuck in watch dog. Replaced CPU socket then board would try to boot but fail. Checked the ROMs and found Pac Man Plus ROMs on the board. Reprogrammed the 4 program ROMs and 2 character ROMs and tested. Board had Pac Man PROMs so the colors were OK.
Board was part of a group of 7 boards sent in for repair. It would not try to boot and was stuck in watch dog. Checked the ROMs and found a rotted pin on 6E and a mixed set of bootleg ROMs for the remaining 3 on row 6. Replaced the bad ROM and reprogrammed the other 3 program ROMs and tested. Board had a Pac Man Plus PROMs at 7E which caused the board to output incorrect colors. Replaced the PROM and tested.
Symptom: high pitched beeps and blips instead of normal sounds
The beeps and blips occurred at the same time and cadence as the normal sounds. Replaced the 74LS273 and checked the PROMs by both checksum and substitution. Replaced the 2 bi-polar RAMs. No change. Compared signals to a working board and found all the enable lines were correct. Replaced the 74LS283 at 1K to fix.