MK arcade sometimes works sometimes not

MKmaster

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I have an Ultimate MK 3 machine that would play for a month or two and then quit working for a few months. Then it would all of a sudden work again. The last time it was working good....the screen would occasionally turn green colored. You would still be able to play the game, but it would just turn green for a few seconds from time to time. Then it quit working again for about a year or more. Then, yesterday....it acted like it was working but the screen was all screwed up and glitchy, and now I can't get it to work again.

The problem is, the board won't power on, but when it does.....the screen is either solid green, or the picture is all glitchy. But even when the board doesn't power on....the screen always does....but it's just a black screen.

Any help will be much appreciated, as I have no idea about repairing these things. Also....please also know that I may not understand any of the terminology of any gizmos inside, so please describe what I might need to fix. I would really appreciate any help.

Oh, also... Could I just buy a new board to replace? Would that fix this problem? I'm afraid if I have to do anything TOO technical, a might screw it up even worse.
 
the reason for your board not powering on is most likely being caused by a faulty power supply. there might be some life left in it, however, and I don't expect you to perform this task immediately (it takes some time and understanding for those that aren't like technologically-inclined) but allow me to explain some fundamentals of how these work.

the power supply, contrary to what most newbies believe, doesn't power anything that's AC driven unless it's a very messed up arrangement. :) AC powered items are 1) the power supply itself 2) the monitor and 3) the marquee light fixture.

the power supply outputs a series of different sized voltages, in the case of MK3 those are +5, +12, and -5. only one of these voltages, however, is what's called "regulated". the most important voltage in any video game is the +5, because that's what's required to "power" the video game board. although it's called +5, that doesn't mean that it's exactly 5.00 volts, in fact, the voltage needs to be a little bit higher than 5.00, more in the realm of 5.10, in order to ensure proper operation. you can actually declare this voltage through the +5 adjustment on the power supply, but it's not something you just turn and hope for the best.

to do this, you need a digital multimeter, which is capable of measuring this voltage so that you get an accurate reading of what your +5 is set at. over time with power supplies that have age and mileage riding on them, this adjustment for lack of a better way of describing it goes OUT OF adjustment. if the power supply still has some life in it, you can adjust this back up to the desired 5.10 volts. otherwise, there are some power supplies that will either be incapable of outputting that high of voltage anymore, or there are some that are just seriously broken.

the power supply that was in my Killer Instinct cab would sometimes go into overload protection mode, which essentially shuts the power supply down, despite having electricity going to it. no degree of adjustment could fix this, I had to replace the unit. that particular one was of the "screw terminal" variety, which means that you attach all the wiring for the different types of voltages to terminals held down with screws.

if you look at your game board, you will find a large black wiring harness plugged into it, and this is called a JAMMA harness. JAMMA was just the name of the wiring standard (because many classic games by different manufacturers used their own wiring pinouts, which meant that swapping games often required a full stripping of all wiring from the game cabinet and replaced with new wiring mated to the new game's board). there are certain pin locations on the JAMMA edge of game boards that take these different voltages, and the wires attached to these pins on the JAMMA harness are what run to the power supply.

there's another kind of power supply that resembles that of a PC XT power supply that has a white block "molex" connector that runs to the JAMMA harness, which makes a direct power supply swap very easy, but I can't tell you what kind of power supply you have, cause I don't know what type of power block Midway put in MK3.

I would say minimize the confusion and just replace the power supply with a new one, but a point to consider is that most new power supplies are adjusted at the +5 setting for 5.00 volts exactly, or for all intents and purposes, you don't know what kind of voltage it's going to be set at either.

switching power supplies, like the kind I'm talking about, only really work unless there's a "load" present, meaning that a game or some other device that requires power needs to be attached or else it won't function properly. the other voltages I've mentioned, like the +12 and the -5, unlike the +5, are merely products of the switching process that the power supply performs, and are also not regulated. it's not uncommon to get readings with a meter on these power rails in the realm of 13.85 volts and -4.89 volts respectively, because these don't really matter all that much, they really only power the sound hardware/amplifier on the MK3 board. it's worth noting that if the power supply is in bad enough condition that it no longer creates +12 and/or -5, you will not have working sound in your game.

however, despite requiring a load, it is perfectly safe to get a rough idea reading of where your +5 voltage is at prior to hooking up your JAMMA harness back to the game board for roughly 10-15 seconds without damaging the power supply. the best part is this reading comes up almost instantaneous and should either give you enough time to make the necessary adjustment or maybe you even have it at a good spot already. anywhere between 5.00 and 5.20 is acceptable here, then with your game plugged in, you can fine tune it. pay mention that your "rough idea reading" can be done at either the +5 and ground terminals on your screw terminal power supply or you can plug the meter probes into the red and black wire holes on a molex type. your final reading should be at the +5 and ground wires on the JAMMA harness (also red for +5 and black for ground) ... this takes a little bit of finesse, because you don't want to slip and start running your meter probes along components that carry electrical current.

I hope this gives you a better understanding of the power supply and how and why all of these things work.

as for the greenish tint on your monitor, this could be caused by any number of reasons.

the good news (I think?) however is that if your UMK3 board isn't powering on, you will not see a faulty video signal coming from the board that's a solid green. the bad news is that narrowing down the cause of the monitor problem not only requires that you resolve what's most likely a power issue first (as I mentioned previously, this might just require a +5 adjustment and not cost you any money at all!). the green tint can either be a maligned adjustment of the green drive/green bias controls on the monitor neckboard (more finesse) or worse yet could be a damaged monitor tube.

I won't give you monitors 101, I'm sure someone else can describe it better and maybe not write a novel doing it.

good luck, and welcome to KLOV.
 
Thanks for the reply, and yes that helped me understand a little better, but I still don't know what the power supply looks like OR what the +5 knob looks like. But I will try to look more into it. Thanks.
 
found the power supply...now what?

Ok. I found the power supply and where it says +5 and 12 and -5 and all that. So I turn the screws to change the power? And if I get a multimeter...how do I use it? Okay....the power supply on mine looks like a grey box with wires going to the front of it vertically along the front of the box. And that's where the voltage screws are at. One more question. Would it hurt to just turn the +5 screw by like a millimeter, just to see if that might fix the problem? I know it's probably not smart to do without a multimeter, but could I try it? Could it like fry my board or something if I turn it too far? Also....which way do I turn the screw to increase the voltage? Right or left? Thanks in advance.
 
Your power supply should look like this:
http://www.therealbobroberts.net/80-0064.jpg

The adjustment is the recessed slotted screw-like head at the top, above the +12V. Don't turn the screws holding the wires on, they're not adjustments, they just hold the wires in place. To turn up the voltage on the one pictured, turn counterclockwise, though yours may be different (you can see counterclockwise because it has H with an arrow pointing counterclockwise).

You can tweak it just a little bit if you'd like to see if it gets better, though I wouldn't turn it very far, and expect to check it with a multimeter shortly (being a little high won't hurt anything short-term, but could damage them if left too long). To check with a multimeter, you'd want to check DC volts with the red lead on the +5V pin of the JAMMA connector and the black lead on the GND pin of the JAMMA connector. You want to check at the board and not at the power supply, since there is some voltage drop between the power supply and the board.

DogP
 
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yeah, just turning the knob is ill-advised, lol.

I have a story about that, I'll keep this one short. I was wrong about the form factor on the molex type btw, that's more of an AT size, the one that was in this Daytona USA I was working on was like an XT. :p

but anyway, yeah, I had the meter plugged in and everything. the +5 voltage was actually WAY too high, and as I was turning the knob to dial it down, the power supply seriously bottomed out to 0.0V. so another important lesson... UNDERvoltage can damage your equipment too.

I wound up yanking the power cord or turning the power supply off immediately when this happened.

I don't know what would necessarily cause this, except maybe very cruddy contacts on the potentiometer (this is essentially a variable resistor... more on that some other time) but I wound up replacing the power supply anyway.

very good though, you have a screw terminal unit. this can both be easier and harder to test with, lol, it's very easy to slip and start running your meter probes across a bunch of screws, and you certainly don't want to cross any of them.

if you inspect the actual box of the power supply, you'll probably find a hole in the side of the case labeled "+5 ADJ." or something along those lines, in fact, it's more than likely a red knob sticking out the side. I'm going to assume you have one of those grey Peter Chou units, they're quite notorious for taking a shit like I mentioned in the first post. when you replace it though, hang onto it, cause there's actually a way to fix them, but you have to replace some electronic components to do it.

it's also highly worth noting that when you adjust these +5's that you do it VERY slowly and subtly, never with any adjustment on a video game do you ever want to start flipping knobs in large doses.

if you want a meter lesson, you basically have to complete the circuit with the probes. they're colored red and black, and it can make a difference in some instances (like testing diodes or transistors) which order the probes go, but for this, just put the red one on the +5, and the black one on ground. then whatever voltage carries between that circuit, the meter will give you the measurement. some expensive meters have what's called "auto-range" and if you get even more expensive, they'll have "auto-sense" as well. the range for a DC voltage test runs from values of 20 volts, 200 volts, 2000 volts... this is your maximum expected voltage on whatever you're testing. for testing +5V, you'll want it set to DC 20V. some meters can figure this out for you, but with a little know-how that's not a problem at all. that "auto-sense" can figure out if it's AC, DC, ohm, diode check, etc. on its own. kind of scary, really...

I wish I had the means for putting together videos, I keep talking about doing it, but I work every single day, makes it difficult to find the time.
 
one more question

yeah that's the same as my power supply. Thanks for clearing that up for me. But will it hurt for me to turn it just a tad to see if it fixes the problem, that way I don't have to go buy a multimeter? Or could I really screw it up by turning it a hair?
 
Turn it a hair. It could screw everything up, but 99% chance it won't. By a hair, I mean like "Hmm... I wonder if it even turned at all?" hair. Turn it in the direction of the + sign

If the screen is all green, etc. though I think your board is bad, that's my personal opinion. When the board doesn't boot up and the monitor is black, are the coin door lights on? The coin door lights are also ran by the 5V, although if the 5v is low the lights will still come on so I guess that won't really give you an exact idea.

Best bet is a multimeter. Go to harborfreight, they're 3.99. Well worth the money.
 
okay, so I turned it by a hair in the + direction. Nothing changed. So I did it in the opposite direction by a hair. Still....nothing changed. Monitor's black....no power to the board. So if I buy a multimeter and get the voltage at exactly 5.10, and it still doesn't work.....should I just buy a new board? Would that be the only other thing if it's not the voltage?
 
Basically... but how do you know there's no power to the board? When you turn the game on, do you hear the speakers pop or anything? Best case scenario at this point is that the power supply is completely dead... still when it did come on, you shouldn't have been having a green screen and all that, if the power's low usually it'll either boot or not boot, and then maybe freeze, etc. but it shouldn't have garbled the graphics. Possible I guess, though.

Definately need to get a multimeter. If you want a decent one go to sears and buy a craftsmen one for 15 bucks or whatever, or you can get the 4 dollar one at HarborFreight and it won't last as long.
 
Problem with power supply or board?

Yeah.....see sometimes it will turn on but very rarely. I'll hear the speakers pop and the game comes on and the lights on the board come on. But most of the time all that comes on is the monitor with a black screen. Do you still think it's the power supply, or is it more likely to be the board?
 
power supply. seriously, I've seen this happen on a few of those power supplies.

has the game EVER worked properly though? that's the big question. I'm talking no green tint.
 
yes. the game worked properly for a few months.....then I'd get a black screen for a few months. then out of nowhere it would work fine again. Then I started noticing that when I was playing it....sometimes the screen would have a green color to it...while I was still playing it and I was still able to see the characters and backgrounds and everything. But it would only do this for a couple seconds then go back to having the right color. Then the more I played it through the next months....It would turn green more frequently. Then it quit working entirley for about a couple years, and I just turned it on yesterday and out of the blue....it worked, and I played a match with Scorpion.....but the graphics were all screwed up. And stupidly I tried jiggling the whole cabnet to see if it would fix itself. And it started to clear up, but then I jiggled it some more, and it quit working again. Like I said.....now I only get a black screen when I turn it on. No popping sound or nothing. But the monitor IS still working. You still pretty sure it's the power supply? How much does one like mine cost, and where can I buy one? And yes....It's a Peter Chou.
 
favorite seller amongst KLOV members is Bob Roberts the only catch with him is he doesn't take credit or paypal, you have to send him a check first upon your first order, and it has to clear, then he sends out the parts.

I personally don't use Bob, as I work for a business that deals with games and order all my parts from Happ Controls instead, but he's a very good guy, he's very knowledgeable of this stuff, and he's got GOBS of parts available.

your black out problem sounds exactly like the one I had with my KI cab (before I restored it to KI it was a carousel of games, Tekken 3, Mortal Kombat 2, etc. :)) and upon replacing the power supply with a Happ Power Pro the problems went away permanently.

the green problem, ok, I thought this was something that stuck for awhile after the tube warmed up or something. your problem sounds like good old "cold solder", which effectively means the solder joints on your monitor neckboard are essentially shit. fixing this is very simple though, permitting you can use a soldering iron halfway decent, you just re-melt the solder joints and it should clear your problem right up.

where at? well, the neckboard has 3 transistors, one for each color gun in a CRT, and a corresponding resistor to match each transistor. if you have shitty solder joints on any of these, you will probably "lose" primary colors (that's red, green and blue, or commonly we call it RGB) and you'll either have a weird tint like a yellow or a purple, or in your case, a green, which more than likely means your problem lies in the red and blue. this can also be caused by failing transistors/resistors, the only surefire way to diagnose such a problem is to start swapping components.

I understand you're a newbie though, and I'm not going to ask the impossible of you. but I'm about 75% certain that your problems can be solved by yourself.

can you take a picture of your monitor chassis? it's the big board in the metal frame tray. that can help us a lot. model numbers help too if you can find anything, but ignore the actual tube and any numbers you find on it -- the TV tube component has nothing to do with the board that drives it. (common mistake by newbs :))

your story makes me want to finish my Multi Kombat rig...
 
There's a lot of shit in the way of my arcade machine right now cause I've moved into a new place and I've been moving shit around....and I'll have to borrow a digital camera from someone. So it might be a week or something before I can take a pic. But thanks for the help so far. I REALLy appreciate it. I've been wondering how to get that thing to work for a while now. I hope replacing the power supply fixes the problem....that would be awsome.

I also thought about cleaning the long black thingy that connects to the board. You know.....It's like the main plug thingy that plugs onto the side of the board. It's long. I don't know what it's called. I think it might be that harness thing you were talking about. Should I try to clean that first? And how do I clean it? Could that possibly be the problem. It would save me some money if it was. Thanks in advance and thanks for all the help so far.
 
that would be the JAMMA harness. if you look at it, you'll find 6 rows of wires and then an empty spot (these are called "keys") and after that another 28 rows of wires.

the 6 row part is where all your power wiring goes in. the black wires are your grounds, the red ones are +5, yellow is +12, and I wanna say -5 is like a blue color, maybe?

if you look further down, you'll a green wire, then a yellow wire under it, and across from those two are a red wire and a blue wire. these wires will run to your video harness, you'll see them attached to the video signal header on your monitor chassis.

I've observed in my MK cab (it's actually a War Gods...) that the pins for the video wiring on the JAMMA harness would start sliding out of the black plastic holder and I would either have missing colors or worse yet my sync wire would come out, so the picture would be a jumbled mess of shit. I wound up replacing the pins with other ones from a chopped MK4 harness I got from an ebay auction and hot gluing the whole thing in place, lol.

I guess what I'm alluding to here is you have a friend or female companion or kid or even a dog (ok, not really a dog) handy, have them watch the screen or set up a big mirror and don't use any major force, but gently wiggle those video wires on the JAMMA harness and see if it affects the picture at all.

you might get lucky and it'll be something stupid like that.

a preferred approach by other KLOV users for cleaning the JAMMA edge (the contacts that the black JAMMA harness slides onto) on game boards is actually a gummy pencil eraser. the eraser trick is also great for cleaning ROM chip legs too, but we won't get into any of that yet.

but yeah, it's a lot of crazy shit to learn all at once, isn't it? its execution once you understand it all is actually very simple though.
 
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