Midway Games

[channelmaniac]

Fixed: MK3 Ultimate
Symptom: Dead

Physical inspection of the board turned up a large (20 gauge!) wire patch on the EPROMs. Replaced that patch with a 30 gauge Kynar wire wrap wire patch. Found one other gouged trace that was broken in 2 places and gouged off the board by what appeared to have been a huge soldering iron. Board booted but had a ROM error. Replace ROM U132. Game played but had scratcy audio. Resoldered the audio output IC as it had been physically hit and the solder joints had cracked.

[channelmaniac]

Fixed: NBA Jam
Symptom: Scratchpad RAM Error

Board would power up with a Scratchpad RAM Error for UJ7. Replaced the bad chip, a 44256 DRAM, with a socketed replacement. Board would then power up and run but would intermittantly give an error on Video RAM UA11.

Replaced the VRAM IC at UA11 - part # MT42C8128, a 256 x 8 SAM + 128K x 8 RAM dual port video RAM chip. Chip is hard to find but can be found on some old Sun Microsystems frame buffer (video) cards from the early 90s. (In this case a Weitek Power 9000 based card by Megatek)

Ran board through the built-in burn-in tests and played a couple of games.

[channelmaniac]

Model: Ms. Pac Man
Symptom: Garbage on screen

Replaced the ROM at location 6H. It had 5 pins broken off of it and was half way out of the socket. Straightened the pins on the V-RAM addresser daughterboard and reinserted it. It had come loose in shipping. Replaced the zip tie holding the daughterboard in place.

The ROMs on Ms. Pac Man are 2532 and NOT 2732.

To retrofit a 2732 you must rewire 3 pins.

2532:
18: CE*
20: Vpp
21: A11

2732:
18: A11
20: CE*
21: Vpp

This can be done by stacking 2 sockets. make the wiring change between the 2 sockets so the EPROM fits in and it all fits into the board.

[channelmaniac]

Model: Galaxian
Symptom: Large color stripes on screen

Board was missing the U and W ROMs. Burned replacement 2716 EPROMs to bring the CPU to life. Large color stripes would change periodically. The ROMs at J1 and L1 were bad. Burned replacement 2716 EPROMs and the board showed a perfect screen.

[channelmaniac]

Model: Galaxian
Symptom: White screen

Game gave a full white screen and no video artifacts. CPU was rebooting itself and the data lines were in a repeating loop for signals. Replaced bad ROM at Z. Pin 13 was broken on the chip.

[channelmaniac]

Model: Ms Pac Man
Symptom: Rebooting at random

Replaced the CPU socket and socket J1 for the ribbon cable on the daughterboard.

[channelmaniac]

Model: Ms Pac Man
Symptom: Will not boot. Single glitching character on screen.

Ms. Pac Man will normally cycle through characters while doing a self test. This board was stuck on 1 character but was glitching that character continuously.

Replaced bad ROM at 6J and the board would try to boot but come up wtih garbage on screen.

Replaced a bad 2114 SRAM to finish the repair.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Pac Man
Symptom: Garbage on screen. Dead.

4 ROMs failed checksum. Burned new EPROMs for 5E, 5F, 6H, and 6J and tested the board.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Pac Man & Mrs. Pac Man
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.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Galaxian
Symptom: Bad RAM 2 error message on screen

This error message is related to the RAM at 3F or 3H. Replaced both RAM chips then the board came up with a Bad RAM 3 message. This indicates a bad RAM at 4FH or 5FH. Replaced the RAM at 5FH to fix that error. Board then came up with a Bad ROM message. Reseated the ROM daughtercard to fix that error.

Board then came up with horizontal lines across the screen. Burned a new character EPROM at 1H to fix the lines.

[channelmaniac]

Model: Galaxian
Symptom: Bad RAM 1

This indicates a problem with the RAM at 7N or 7P. Replaced both RAM chips to fix the error. The game had horizontal lines across the screen. Replaced the ROMs at 1H and 1K to fix the lines.

[channelmaniac]

Model: Galaga
Symptom: RAM 2L Error

This board was frustrating. RAM 2L bad. Replaced it. RAM 2H bad. Replaced it. RAM 2L bad... RAM 3L bad... RAM 3H bad...

Cleaned the pins on the custom IC at 1H on the video board to fix the error.

[channelmaniac]

Model: Galaga
Symptom: No characters on screen

The player and enemies were both missing. Cleaned the pins on the custom chips on the video board.

[channelmaniac]

Model: Galaga
Symptom: Cannot control Player 1. Enemies go in circles then disappear

This was odd. Game self tested fine and coined up. Player 1 controls were non responsive. Couldn't fire and couldn't move. When enemy ships came down the last one tried to peel away and would go in circles for about 10 seconds then disappear. Once it disappeared the next wave came and the last one repeated the circling and disappearing act.

Checked the ROMs on the CPU board. Found EPROM 3300 was for revision 2 of the Galaga software while the rest of the ROMs were for revision 1. Replaced the EPROM with one holding the correct code to fix the game.

[channelmaniac]

Model: Galaga
Symptom: Random lockups

Board would lock up even during self test. Could tap on the board and cause it to lock up.

Replaced the 3 Z80 CPU sockets. The old TI sockets were making intermittent contact with the chips.

[channelmaniac]

Game: Galaga
Symptom: Locks up after the initialization explosion sounds

The ROMs on this board were Namco instead of Midway with the exception of the ROM at 3M. Replaced it with one programmed with the Namco version of code.

[channelmaniac]

Game: Galaga
Symptom: Faint digital artifacts instead of music.

Resistor pack RM2 was broken. Replaced resistor pack and artifacts were gone. Music was still missing.

The 74LS273 chip at 3B had inputs but no outputs. The clear line was being held high, which is correct. The clock line was cycling during explosions but when high when music was supposed to play. This line is controlled by the PROM at 5C.

Replaced the PROM and the music played as it should.

Read the PROM in the EPROM programmer (7611 which crossed to an 82S129) and it read good. The code didn't change when reading multiple times. Ran the code through ROMIDENT - It's a PAC MAN PROM chip for location 3M. Someone stuffed the wrong PROM on the board.

[channelmaniac]

Model: Galaga
Symptom: Passes RAM tests then instead of explosion sound & crosshatch it dies

Replaced 3 CPU sockets. Board would then get to the point where it says RAM OK then the screen slowly paints white then the board resets.

Checked the EPROMs. Found 2 were for Galaga set 2, 2 were for the fast shoot hack, the ROM at 3J was bad, and the ROM at 3E was for Bosconian!

Replaced the ROMs and the board came right up.