Faulty Mortal Kombat 1 MK1 Y-unit boards

[xrodney]

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

[xrodney]

no replies on this?

[xrodney]

there are no techniians that can help?

[Kevin Mullins]

Board repair, especially on one like those can be difficult to troubleshoot at times.

FIRST thing I would do is check the power supply.
A weak power will also cause weird symptoms like you describe and may need turned up a bit.

[xrodney]

other boards work with the cabinet, so the fault is in the board

[Beretta]

not necessarily, the board could like more voltage, or it might not tolerate high voltage, check whats coming out of the PSU to see where it's at.

if it's a little low then bump it up a little.. if it's higher then normal drop it down a bit..

it might not be the problem but it's quick and easy thing to eliminate.

[ctozzi]

Did you get the control panel yet ?

[Kevin Mullins]

not necessarily, the board could like more voltage, or it might not tolerate high voltage, check whats coming out of the PSU to see where it's at.

if it's a little low then bump it up a little.. if it's higher then normal drop it down a bit..

it might not be the problem but it's quick and easy thing to eliminate.

Absolutely......
I've taken non-working MK boards out of machines, hooked them up to my test rig and they worked fine...... put them back in the machine, bumped the voltage up a tad..... all is good.
And this was after measuring the voltage from the power supply which measured fine for most other boards.

So take the 2 minutes to measure the voltage on the power supply WHILE the MK board is connected and let us know what it is.
I've seen finicky MK boards that wanted 5.3 volts where 5.1 was good for many other boards.
Heck, half a volt can make all the difference in the world sometimes.

Welcome to the arcade world.

[xrodney]

i will try that. but the boards where advertised as non working when i bought them.

if that does not work, what is the next step?

ctozzi, cpo not here yet

[xrodney]

ps, i am new at this.  where do i measure the voltage, and how do i turn up the voltage?

[Beretta]

do you have a multi meter?

if so set it to DC 20, then stick the black probe on one of the grounds on the power supply.

then use the red probe to check the other voltages, 12, 5, -5

there is a dial on the power supply turning it wil increase or decrease the voltage levels.

dont over do it.. example running a 12 at 15 or something is probably not a good idea..

but say running 12 at 13 and still no change then it's probably not the voltage.

you're basically tweaking it 1 volt or so one way or the other.


for the board that comes up but is faulty.. couple of things.

1. have you tried taking up the roms that it says are bad and then putting them back down? they might just need to be reseated.

2. the other board you're taking roms off to fix the one with bad roms.. are the two boards using the same version of roms?

There was several revisions of MK, if you're say mixing v1 and v2 roms together i would imagine it's gonna call it a bad rom even though it might actually be good it's not the version of the rom it's expecting.. i assume it probably does this with some sort of CRC check, so if it's not exactly what it wants it's gonna say its bad.

beyond making sure the roms are the same version and resenting them.. i do not know.. it could be a million things, anything from a loose connection, to a blown resistor or anything.