Faulty Mortal Kombat 1 MK1 Y-unit boards

xrodney

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I have a couple of questions. I have 2 faulty mk1 y-unit boards. One has 2 whole banks of rom faulty, the other other justa black screen, no boot up.

The one with faulty roms (from u95 to u98 and u111 to u114), I replaced one rom to test it but still giving a faulty rom.

The other, LED 2 does not blink so there is no activity. How can I fix these? Any thoughts

Rodney
 
I have about 8 of these I'd like to fix as well. The problems range from faulty picture, to know picture. Not sure if they are "Y" unit boards though, they look like plain MK boards.
 
From what I understand, the "Y Unit" boards are the main boards for MK, High Impact Football, etc... the auxiliary (sound) boards are called something else.
 
From what I understand, the "Y Unit" boards are the main boards for MK, High Impact Football, etc... the auxiliary (sound) boards are called something else.

yeah, the sound boards vary. I have High Impact Football and a couple MK1s and I believe the earlier Williams games use a different sound board that the latter Midway games toward the end of the hardware's life span.

not sure what stuff like Total Carnage runs.

anyway, OP, I promised I'd give you some feedback on what to look for. :)

your first board with the 2 bad banks of roms, I think you should check some basic stuff like the traces coming off probably the first and last rom sockets to see if there's any broken traces in the series. I highly doubt that 2 whole rows of roms would have dirty sockets, but I guess it doesn't hurt to look.

your second board with the black screen, I'd say if you're adept at handling a digital multimeter to check your voltages at the JAMMA harness OR rather check the JAMMA harness itself ... see if anything's cooked on it. black screen could be something as simple as the board not getting juice, which probably explains why you're not getting LED activity.

maybe get us some close up pictures; board #1 I'd say try to get the top and bottom of the rom sockets, and board #2 I'd say get a picture of the JAMMA edge or any other portions of the board that look like they may have got fried. :)

then maybe you'll get more guys with technical expertise to reply. I've never tried repairing any of these boards before, so I'm just throwing out some things to check.
 
Thank you for your reply mecha187. i will try the stuff you said. i am not a technician, so i will have to learn all the stuff you said hehe. by traces you mean the yellow/gold lines in the board right?

reg the jamma harness, other boards work perfectly with this cabinet. maybe with the second board, i should start from the edge connector

thanks, i will post videos and pics of the faulty boards soon

Rodney
 
yeah, the sound boards vary. I have High Impact Football and a couple MK1s and I believe the earlier Williams games use a different sound board that the latter Midway games toward the end of the hardware's life span.

not sure what stuff like Total Carnage runs.

anyway, OP, I promised I'd give you some feedback on what to look for. :)

your first board with the 2 bad banks of roms, I think you should check some basic stuff like the traces coming off probably the first and last rom sockets to see if there's any broken traces in the series. I highly doubt that 2 whole rows of roms would have dirty sockets, but I guess it doesn't hurt to look.

your second board with the black screen, I'd say if you're adept at handling a digital multimeter to check your voltages at the JAMMA harness OR rather check the JAMMA harness itself ... see if anything's cooked on it. black screen could be something as simple as the board not getting juice, which probably explains why you're not getting LED activity.

maybe get us some close up pictures; board #1 I'd say try to get the top and bottom of the rom sockets, and board #2 I'd say get a picture of the JAMMA edge or any other portions of the board that look like they may have got fried. :)

then maybe you'll get more guys with technical expertise to reply. I've never tried repairing any of these boards before, so I'm just throwing out some things to check.

Not to derail too much, but what could it mean if you're getting no picture, 5v and gnd testpoints are spot on, and only one LED (of the two) lights on a High Impact PCB?
 
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