Author Topic: Midway Games (Read 104203 times)

channelmaniac · « **Reply #320 on:** June 07, 2020, 06:39:20 PM »

Model: Mortal Kombat 3
Symptom: U49 CMOS RAM Error

U49 is not the backup RAM, U63 is. Replaced bad backup RAM only to have the power to it disappear. Patched a corroded trace and tested.

channelmaniac · « **Reply #321 on:** October 08, 2020, 10:02:51 PM »

Model: Ms Pac Man
Symptom: No sprites on screen

Traced backwards from the motion RAM circuitry to find the 74LS174 at 1K had a stuck output on pin 15. Replaced the IC and tested.

channelmaniac · « **Reply #322 on:** October 21, 2020, 03:34:53 PM »

Model: Mortal Kombat II
Symptom: All graphics ROMs fail testing

Board had attempted reflow done to the custom DMA controller IC.

Upper address line signals were missing off the Graphics ROMs. Fixed a shorted pad and reflowed the 2 sides of the custom that someone had attempted before. Replaced bad 74LS374 at UE17 and bad PAL at UE18. Tested.

channelmaniac · « **Reply #323 on:** October 21, 2020, 10:13:33 PM »

Model: Mortal Kombat II
Symptom: Dead. Missing ROMs

Programed replacement program ROMs and installed them to find graphics corruption. Replaced bad RAM at UB11 and tested. Board failed CMOS RAM tests. Patched bad trace to the RAM's /CE line but that did not fix the issue. Replaced the CMOS RAM and tested.

channelmaniac · « **Reply #324 on:** October 21, 2020, 11:33:06 PM »

Model: Mortal Kombat II
Symptom: Dead. Missing parts.

Patched gouged trace and replaced missing program ROMs and a missing PAL. Board would boot but ROMs tied to data bits 0-7 would pass but 8-31 would not. Replaced 3 bad 74ALS245 chips at UH13, UF15, and UF16 and tested.

channelmaniac · « **Reply #325 on:** October 25, 2020, 09:58:11 PM »

Model: Galaxian
Symptom: No moving enemies

This one was interesting. Someone replaced some of the attack RAM with the wrong type. Three of the 27LS00 (256 x 1 bit) RAMs were replaced with 82S25 which are 16 x 4 (64 bits) and of the wrong pinout. Replaced the three RAMs with 82S16, a compatible RAM and tested.

channelmaniac · « **Reply #326 on:** October 25, 2020, 09:58:33 PM »

Model: Galaxian
Symptom: Hum

Recapped board and tested.

channelmaniac · « **Reply #327 on:** October 25, 2020, 09:59:26 PM »

Model: Galaxian
Symptom: Squished enemies and double text on screen

Replaced a missing character ROM at 1K and 74LS86 chips at 4B and 5B. Tested.

channelmaniac · « **Reply #328 on:** October 25, 2020, 10:01:54 PM »

Model: Pac Man
Symptom: Garbage on screen

Replaced a bad RAM at 4N and three bad ROMs at 6E (dead), 6F (pin rot), and 6H (pin rot.) Repaired a burnt edge connector and replaced the power caps. Tested board and found the ROMs at 5E and 5F were for Ms. Pac Man. Replaced them at the customer's request with Pac Man versions.

channelmaniac · « **Reply #329 on:** November 16, 2020, 12:14:44 AM »

Model: Galaga
Symptom: Dead

Replaced all the old style 24, 28, 40, and 42 pin sockets with good quality dual wipe sockets and replaced unencapsulated resistor packs. Replaced missing ribbon cable and tested. Board would crash like crazy and had clock issues. Replaced bad 6116 SRAM and retested. Replaced bad 74LS368 on the video board and CPU board. Replaced bad 74LS107 on the CPU board. Board still had an unstable main clock after 3 bad ICs were replaced. Replaced the main crystal and had a solid clock afterwards, but the board would still crash. Replaced bad bipolar PROM at 5C and tested.

channelmaniac · « **Reply #330 on:** November 16, 2020, 12:16:06 AM »

Model: Galaga
Symptom: Dead

Replaced all the old style 24, 28, 40, and 42 pin sockets with good quality dual wipe sockets and replaced unencapsulated resistor packs. Replaced a missing 00xx custom and missing L ROM. Board would boot but had no sound. Replaced sound amplifier IC and tested.

channelmaniac · « **Reply #331 on:** November 16, 2020, 12:17:57 AM »

Model: Galaga
Symptom: Dead

Replaced all the old style 24, 28, 40, and 42 pin sockets with good quality dual wipe sockets and replaced unencapsulated resistor packs. Replaced 6 missing 2114 RAMs and tested. Board would boot but crash during attract mode. Replaced incorrect ROM at 3L (Namco code vs. the other ROMs having Midway code) to fix that issue. Audio played but had a thumping in it. Recapped the audio section and retested.

channelmaniac · « **Reply #332 on:** November 16, 2020, 12:19:43 AM »

Model: Galaga
Symptom: Bad Audio

Board had previous repair attempts.

Replaced 4 24-pin sockets and 3 28-pin sockets with good quality dual-wipe sockets to get the boardset stable. Replaced a bad 7489 RAM at 2A to fix the audio issue.

channelmaniac · « **Reply #333 on:** November 23, 2020, 11:27:54 PM »

Model: Pac Man
Symptom: Stuck in boot loop

Replaced bad 2114 and tested. Recapped board and retested

channelmaniac · « **Reply #334 on:** November 23, 2020, 11:28:27 PM »

Model: Pac Man
Symptom: Hums

Recapped PCB and checked the rectifier diodes. Tested.

channelmaniac · « **Reply #335 on:** November 23, 2020, 11:29:17 PM »

Model: Pac Man
Symptom: Incorrect colors

Replaced incorrect PROMs at 7F and 4A. They were from Pac Man Plus. Recapped the PCB and repaired a burnt edge connector. Tested.

channelmaniac · « **Reply #336 on:** November 23, 2020, 11:33:31 PM »

Model: Pac Man
Symptom: Incorrect colors and no sound

Board had previous attempted repairs with some damaged traces.

Recapped the PCB then replaced the Pac Man Plus PROMs at 7F and 4A to fix the color issue. Replaced a bad 7489 and 4066 in the sound circuit. Fixed a broken trace under the socket of the 74LS273 and replaced both the socket and the 273. Still no sound. Started tracing through the rest of the previous work done and found the resistor pack on the PROM at 3M was installed backwards, tying the Open Collector outputs of the PROM to ground instead of tying them to +5v. Replaced the 6 pin resistor pack with a 5 pin and installed it properly to fix the sound issue. Tested. Board would intermittently not read the DIP switches properly and moving the joystick would cause the game to step to the next level. Replaced a bad socket and the 74LS138 at 7J and retested successfully.

channelmaniac · « **Reply #337 on:** November 23, 2020, 11:35:22 PM »

Model: Ms Pac Man
Symptom: Random reboots.

Recapped PCB and fixed burnt edge connector. Replaced bad ribbon cable to daughterboard and tested.

channelmaniac · « **Reply #338 on:** November 25, 2020, 02:26:09 AM »

Model: Ms Pac Man
Symptom: Reboots at random

Board was DC converted

Replaced missing diodes at D7 and D7, missing 4 ohm 10 watt resistor, and repaired the burnt edge connector. Replaced dirty sockets at 6H and 6J that had some kind of spill down inside them. Tested. Recapped PCB and retested.

channelmaniac · « **Reply #339 on:** November 25, 2020, 11:16:16 PM »

Model: Pac Man
Symptom: No Green Output

Board had attempted repair damage.

PCB arrived dead. Replaced bad previously replaced 74LS161 at 3S and patched two damaged traces under it. Replaced power caps and tested. Cleaned legs on the PROM at 4A to fix graphic and color issues. Board would run but would reset at random. Tapping the board would also cause it to reset. Discovered that the 10uf cap in the reset circuit was bad and you could make the board reset at will by simply tapping it lightly. Replaced cap and tested.

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Author Topic: Midway Games (Read 104203 times)