Mortal Kombat Monitor Problem

I recently aquired a near-mint condition Mortal Kombat arcade. Everything is in excellent shape, artwork has no sunfade and everything looks all peachy! By far the machine I'm proud of the most! Even the monitor is in excellent condition, no burn-in, no geometry issues... but there is one small problem. On the Mortal Kombat machines, they have an adapter attached to the monitor chassis that gives you the adjustment pots in the front of the cabinet as opposed to the rear, and unfortunately the contrast pot has disintigrated.

I can still make out the picture by adjusting the black level pot, but after shorting a few traces I can clearly see it's *nothing* compared to what it could look like had that contrast pot still been working. I was going to switch the broken pot with another pot (vertical hold?) on the daughter board, but I realized that the monitor cant function without it (I thought it held it in memory). So long story short, has anyone ever repaired one of these daughterboards before? I think the contrast pot is 10k F if I'm correct.

Thanks in advance!
Shmenge

You should be able to desolder the old pot and put a new one in its place granted the PCB doesn't have corrosion, hairline fractures, etc. It should be a pretty easy fix...

-B

The values are likely to be quite different anyway, contrast 10 K and V hold probably around 250 K.

You should have no problem locating a suitable pot. Try Jameco.

As a temp fix - short the center (wiper) connection to either side of the pot, one side will give max contrast, the other minimum.

Yeah thats something I noticed, when I shorted the contrast just for a second, it would max the contrast out, and then slowly fade to minimum. I can live with it like this, it's finding a pot that fits it thats going to be the hardest part.

Edit- also, is there a reason a lot of arcade monitors have the "screen" pot on the flyback glued down? I saw this on a few of my cabs and started wondering.

I have an old sega volume potentiometer I could use, but I was wondering what each signal does? Like, at the top of the pot there are three places to connect the wires, how do I know which one goes where? (or is it a trial and error thing?) Also, the original pot reads "10K (small triangle thingy) F", and the sega one I have reads "B 5k ohms". Does this matter?

Edit - I just wired it up because I'm an impatient son of a gun, and sure enough, it worked! My only question is how long. Plus I dont like the fact that theres a pot hanging off the side of a pcb... something tells me gravity will intervien and all of a sudden I'll be in the middle of playing when the contrast maxes out out of nowhere

ShmengeTravel said:

Edit- also, is there a reason a lot of arcade monitors have the "screen" pot on the flyback glued down? I saw this on a few of my cabs and started wondering.

Click to expand...

Yes...

As the monitor heats and cools that cycle could cause the knob to slowly drift/turn. They put a little dab of junk on there to keep it in place. If you readjust it simply use a little dab of fingernail polish (NOT THE METALLIC FLAKE TYPE!) to keep it in place.

RJ