Midway Games

[channelmaniac]

Model: Galaga
Symptom: No sounds except explosions

Sound PROM at 5C was incorrect. It had a PROM for 1D in the socket.

[channelmaniac]

Model: Galaga
Symptom: Reboots constantly

This is different than the bad CPU socket problem in that it wasn't stuck at RAM OK but rather as soon as the crosshatch then the text came on the screen it rebooted. The Reset line on CPU #2 and 3 came active for a VERY short period of time then the game reset.

Swapped out the CPU sockets. Subbed out the custom chips. Nothing. On a whim I turned off each DIP switch and found by playing with them that when DIP switch #3 at 6J was on it would cause the system to lock up when running or to constantly reset when booting.

Replaced the 74LS151 at 4K and the 74LS368 at 5A. Problem still there. Checked the EPROMs again. They were all checking good on the programmer. Swapped out the first 2 program EPROMs. Nothing. On a whim I burned a new set of Williams EPROMs (these were Namco) and swapped out all the EPROM.

Problem fixed.

[channelmaniac]

Model: Galaga
Tip: Replacing PROMs

The PROMs used on the board are Harris 7611. These are 256 x 4 bit bipolar PROMs.

Other PROMs can be used to replace this one, including:

• 5623
• 6301
• 7052
• 74S287
• 82S129
• 93427
• AM27S21
• F93427PC
• 63S141

I have tubes and tubes of Fairchild's 92446 - a 512 x 4 bit bipolar PROM. If you take the code for the 256 x 4 bit PROM and duplicate in the upper half of the PROM these can successfully be substituted for the smaller PROM.

[channelmaniac]

Model: Galaga
Symptom: flickering garbage on screen.

Board had been worked on before by a ham fisted technician. Removed their soldering work at 2K, 2L and 2M. Cleaned up the bridged soldering mess under the socket at 2L, installed new sockets, and installed new chips.

Board now had a solid white screen with garbage characters on the top row. During the attract play when the boss ship captures the player's ship that part is visible on the screen under the garbage but the ray is mixed up.

Pin 19 on 2L was stuck high. The input, on pin 18, was missing because of a damaged platethru. Ran a wire jumper and played the game.

[channelmaniac]

Model: Galaga
Symptom: Multiple graphics problems

Another "attempted repair" by a ham fisted technician. This board had flickering video, incorrect text, bad colors, double characters, and a lot of vertical lines through the screen.

Found a bad trace connecting Pin 1 of 4A. 4A drove address line A9 for 4 of the video RAM chips. Fixed the trace to cure the vertical lines problem.

Found a bad trace connecting pin 1 of 3D. Patched the trace to fix the double characters.

Tapped the board and found that if the EPROM at 4L was tapped the screen flickered and the text changed. Replaced the bad socket to fix the flickering and incorrect text problem.

Repaired a bad trace on the video output resistor ladder to fix the color problem.

[channelmaniac]

Model: Galaga
Symptom: Multiple video problems

Another board from a ham fisted repair attempt.

Board had no video. Cleaned the pins on the custom chips at 00xx, 7xxx, and 02xx. Repaired bad pins on those chips and piggybacked an extra socket on the 00xx and 02xx chips to protect the fragile pins.

Board now has video but the video has blue lines through it. Replaced a broken SIP resistor pack at RM5 to fix the blue lines.

Board now has video but the layout is wrong. Ships are doubled, text and player ships stack vertically up the left side of the screen and the crosshatch has many tiny squares down the left side. Patched a trace between pin 11 of the 00xx and pin 21 of the 07xx chips.

Board now has video but colors are wrong. Replaced all the cut and resoldered resistors in the output ladder. Patched 3 damaged traces. Now the video looks great and I set a new personal high score.

[channelmaniac]

Model: Galaga
Symptom: locks up

2 boards with the same symptoms... Passes RAM/ROM tests, makes the explosion sounds, then locks up randomly. When it freezes up the characters on the screen may or may not disappear. Most of the time the screen will then flip upside down. It might play for a minute or 3 then it will start doing strange things.

Symptoms:

• Starfield starts flickering fast
• Enemies wings move a LOT faster
• Enemies MOVE a lot faster

Tested the ROMs with the EPROM programmer and by substitution. Cleaned the custom chip legs and swapped out the 7xx, 6xx, and 51xx chips. Replaced the ROM sockets and CPU sockets on one of the board sets. The logic probe showed the CPU at 4E was halting. I noticed that when shorting the IRQ pin to D0 (15 to 16) on that CPU the board would run (strangely) and not lock up. Replaced the CPU on each board and played a couple of games.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

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.

[channelmaniac]

Model: Pac Man
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.

[channelmaniac]

Model: Ms. Pac Man
Symptom: Dead. Had shipping damage due to insufficient packing and no zip ties on daughtboards.

Board arrived with shipping damage. Once damage was fixed, the board was still dead.

The VRAM Addresser and Z80 Sync Bus Controller modules were both floating around loose in the box. They weren't zip tied into place.

Removed the bent up socket on the bottom of the VRAM Addresser board and replaced it. Straightened the pins on the Z80 Sync Bus Controller board. Board symptoms: Dead.

Replaced bad CPU. Game would play but had no audio. Used the logic probe and found audio signals at the output of the sound section. Used the oscilloscope and verified audio was getting to the final amplifier IC's input pins. Replaced the bad audio amplifier IC and the filter cap on the 12v line.

It's uncommon to have a blown audio amplifier IC. If a Pac Man series or Galaxian series board is put into a Neo Geo multislot cabinet with a JAMMA adapter, the audio IC will get finger blistering hot and burn out. The multislot MVS boards are wired differently and this stresses the audio output IC.

[channelmaniac]

Model: Galaxian
Symptom: Constant background tone when playing

Galaxian is supposed to have a varying tone in the background when playing. It gets faster and faster as the game is played. On this board it was only playing a single continuous tone.

The troubleshooting guide points to a problem with a 555 timer and the 2 GE6015 transistors. The 555 timer had already been replaced by the customer. Checked the 2 GE6015 transistors and they were good.

Checked C15, C16, R15, R16, R17, R18, R20, and R21. All checked good. Swapped the 555 timer chip since it was CMOS and the original part wasn't. No change. Checked the resistance from pins 2/6/7 of the 555 to +5v and ground. It read 1200 ohms to both power and ground. Swapped out the LM324 quad op-amp chip to repair the board. It connected to pins 2/6/7 of the 555 timer chip and had an internal short to power and ground on the input.

[channelmaniac]

Model: Galaxian
Tip: Transistor cross reference

The Galaxian sound subsystem uses 2 GE6015 transistors to oscillate the background audio. These transistors are no longer made and are not in the NTE cross reference book.

They can be successfully replaced with the easy to find 2N3906 transistors.

[channelmaniac]

Model: Mortal Kombat 4
Symptom: Board had multple RAM failures and no video sync

Replaced U74, a surface mount 74LS07 and replaced a burnt zero ohm resistor on the video ground to fix the video sync problem.

Resoldered U66, U32, U62, and U63 then resocketed U48 to fix the RAM issues and random reboot issues. Board can now be jostled briskly without rebooting.

Reset button was dead. It had liquid (rodent?) damage. Cleaned the board and replaced the switch.

[channelmaniac]

Model: Pac Man Jr.
Symptom: Burnt edge connector.

Repaired connector traces with copper trace tape and tested.

[channelmaniac]

Model: Galaga
Symptom: Dead. Stuck in reboot loop.

Removed a 68B09 CPU from socket 4H and installed the proper 51xx custom Namco chip. Replaced the 3 Z80 CPU sockets and the 6 ROM sockets. Board would still either be stuck in a reboot loop or act dead. When it acted dead the CPU was stuck in a reset loop. If the board was slightly flexed it would try to boot.

Replaced a bad socket on the 7xx chip. The VBLANK* signal was not getting to IC6A, pin 1, to keep the watchdog signal from resetting the CPU. Reset the DIP switches to factory settings and tested.

The board was now missing all text on the screen except the very top row, which was green instead of red. When playing game the flags showing the level were the wrong color and missing lines and the line showing the credits was missing.

This is handled by the EPROM at location 4L. It is fed by a 74LS273 at location 2L and 74LS86 at location 2N. These were good, the EPROM tested good by a programmer and by substitution. All the signals were correct on the custom chip at location 4H. The IC at 4H outputs the control signals for those images out pins 11 and 12 to pins 5 and 6 on IC 2N, a PROM. Checked the PROM and found that pin 9 was folded under the chip. This is the D3 output. Straightened the pin and tested the game.

[channelmaniac]

Model: Galaga
Tip: Stuck in reboot

If the DIP switch for Video Freeze (6J, switch 5) is left on and the game restarted it will be stuck in a reboot loop until the switch is turned OFF. The effect is different than when you have bad CPU or ROM sockets on the CPU board where it shows RAM OK then reboots. In this case, it is showing ROM OK, RAM OK, and the rest of the normal text before suddenly rebooting.

If after replacing those CPU and ROM sockets (which should be done on ANY Galaga game that still have factory sockets) the board is still rebooting then check that switch. You'll save yourself headaches.

[channelmaniac]

Model: Galaga
Symptom: Multiple problems. Board had been worked on before.

Board would boot but had no explosion sounds and would not accept inputs properly. Sprite graphics were missing every other vertical line and there were vertical blue noise 'tails' on the bottom of the screen.

CPU board: Replaced missing 00xx and 06xx ICs. They were in the box with the board but were not installed and had missing pins. Repaired broken pin 28 on custom IC 55xx to fix the input and sound problem.

Video board: The sprite problem would come & go with flexing the PC board. Replaced a bad socket and trace on pin 3 of 1C. Resoldered the SRAM socket on 2148 SRAM at 6B. The ground pin was not soldered properly. Resistory pack RM7 was bad and causing the blue vertical streaks.

[channelmaniac]

Model: Galaga
Sympom: Dead. No video output.

Board was previously worked on and had problems on both the CPU board and Video board.

CPU board: Fixed one badly jumpered trace. Replaced a bad EPROM at 3K, the D1 and D2 lines were shorted internally. Replaced bad sockets on the CPU at 4M and the Namco custom chips at 4D, 2L, 2J, 2H, and 2E.

Video board: Cleaned board. The 6MHz clock signal was not getting to pin 1 on the 02XX IC at location 4H. Replaced bad sockets on Namco custom chips at 1N, 1L, 1H, and 4H. Fixed a broken leg on the 07XX chip at 1N and cleaned the legs on the custom ICs at 1N, 1L, 1H, and 4H. Cleaned the legs on the SRAM IC at 1K to finish the repair.

[channelmaniac]

Model: Ms. Pac Man
Symptom: Dead

Removed the daughterboard and powered up the system without it to isolate problems. Some of the normal startup RAM tests are occurring but when it is supposed to switch to another area of RAM it reboots. Rebooting is NOT being kicked off by the watchdog timer.

Found that when the board was flexed it would boot normally. Found a cut on the trace coming from pin 3 of the 74LS367 buffer chip at 6R. This was the AB10 signal line feeding the 74LS139 2 to 4 selector that controlled the CS* (Chip Select) line on the 2114 SRAM ICs. Repaired the trace and the board would play as a Pac Man game with corrupt characters, normal since the Ms. Pac Man ROMs were in 5E/5F.

Replaced a broken 40 pin connector on the daughter board ribbon cable, reassembled the game and tested.

[channelmaniac]

Model: Galaxian
Symptom: No Sync

Replaced a bad 74LS08 at location 6H and tested.

[channelmaniac]

Model: Pac Man
Symptom: Dead

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.

[channelmaniac]

Model: Cruis'n USA
Symptom: Dead

Board was paired with a Cruis'n World and someone tried to troubleshoot by swapping parts.

Sorted out the ROMs with an EPROM programmer and eplaced 1 missing program ROM. Swapped the correct PALs back on the board and tested the game.

[channelmaniac]

Model: Pac Man
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.