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Author Topic: Midway Games  (Read 100752 times)

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Offline channelmaniac

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Re: Midway Games
« Reply #20 on: May 07, 2014, 08:38:07 PM »
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.
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Re: Midway Games
« Reply #21 on: May 07, 2014, 08:38:16 PM »
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.
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Re: Midway Games
« Reply #22 on: May 07, 2014, 08:38:30 PM »
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.
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Re: Midway Games
« Reply #23 on: May 07, 2014, 08:38:39 PM »
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.
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Re: Midway Games
« Reply #24 on: May 07, 2014, 08:38:48 PM »
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.
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Re: Midway Games
« Reply #25 on: May 07, 2014, 08:39:04 PM »
Model: Galaga
Symptom: No sounds except explosions

Sound PROM at 5C was incorrect. It had a PROM for 1D in the socket.
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Re: Midway Games
« Reply #26 on: May 07, 2014, 08:39:17 PM »
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.
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Re: Midway Games
« Reply #27 on: May 07, 2014, 08:39:30 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

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Re: Midway Games
« Reply #28 on: May 07, 2014, 08:39:44 PM »
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.
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Re: Midway Games
« Reply #29 on: May 07, 2014, 08:39:56 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

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Re: Midway Games
« Reply #30 on: May 07, 2014, 08:40:17 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

http://www.arcadecomponents.com

Offline channelmaniac

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Re: Midway Games
« Reply #31 on: May 07, 2014, 08:40:26 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

http://www.arcadecomponents.com

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Re: Midway Games
« Reply #32 on: May 07, 2014, 08:40:35 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

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Re: Midway Games
« Reply #33 on: May 07, 2014, 08:40:45 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

http://www.arcadecomponents.com

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Re: Midway Games
« Reply #34 on: May 07, 2014, 08:40:55 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

http://www.arcadecomponents.com

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Re: Midway Games
« Reply #35 on: May 07, 2014, 08:41:09 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

http://www.arcadecomponents.com

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Re: Midway Games
« Reply #36 on: May 07, 2014, 08:41:25 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

http://www.arcadecomponents.com

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Re: Midway Games
« Reply #37 on: May 07, 2014, 08:41:35 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

http://www.arcadecomponents.com

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  • Few things are better than fixing an old game...
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Re: Midway Games
« Reply #38 on: May 07, 2014, 08:41:44 PM »
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.
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Offline channelmaniac

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  • Few things are better than fixing an old game...
    • Arcadecomponents.com - Looking for hard to find chips?
Re: Midway Games
« Reply #39 on: May 07, 2014, 08:41:52 PM »
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.
I have too many hobbies! Electronics, gunsmithing, Miatas, arcade games, metal detecting, etc...

http://www.arcadecomponents.com

 

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