Tell me why this wouldn't work: replacing arcade power supply with PC pwr suppl

[quarterback]

I've got a 'dead' cab that I bought last week at an auction.  After taking my multi-meter to the switching regulator power supply terminals, I've found that I'm not getting the voltage I'd expect (only 1.6v from the 5v terminals and only 4v from the 12v terminal)

This leads me to believe that the PS is bad/needs replaced/repaired.  

But riddle me this... I have an extra computer power supply somewhere in the basement, and PC power supplies ALSO put out +5v and +12v.   Would it be possible to hook up a computer PS instead of buying a new 'arcade' power supply?  Has anybody done this?  I searched the forums but didn't find anything.

My biggest concern is that the existing arcade power supply has 220v (212v actually) going into it and the 12v output also says "25A".  I don't think a PC power supply could crank out that kind of amperage so maybe it's not strong enough.

Anybody?

[menace]

You pretty much answered your own question--the computer power supply may not supply the amperage as well as the fact that some power supplies need to have current drawn relatively evenly across the 12V and 5V lines--for instance if the game drew heavily on the 5 sometimes the 12 will dip and if the  game drew heavily on the 12 then somettimes the 5 will dip--you should just crack open the arcade power supply and see whats the problem--i fixed a couple that just had bad fuses and one blew a cap--no big deal at all.

[quarterback]

you should just crack open the arcade power supply and see whats the problem--i fixed a couple that just had bad fuses and one blew a cap--no big deal at all.

Yeah, but I suck at soldering and I really don't know if I could even diagnose the problem since I'm so new at this.

I was able to find some other things via Google that imply that people have done this with a PC supply.  Both here and here

I bought the cab assuming everything inside was dead.  This was fine because I was really only looking for an empty Mame cab anyway and figured I'd use a PC monitor or TV.  BUT, if the arcade monitor DOES work, then I want to use it.  Right now I can't tell if the monitor works or not because I can't even get the game to power up.   I'm not really interested in spending any more money on parts only to find out that the monitor doesn't work, so I'm looking for a way to figure that out first.

How about this question:  What exactly is the switching power supply powering?  Is it just the PCB and lights?  If so, then I can't imagine it pulling that much power and a PC supply might work.

So, anybody think I'll do myself/my machine any irreparable damage if I try a PC power supply?

[quarterback]

Okay, a new wrinkle here.

I took the power supply out of the cabinet (disconnecting all the wires except for the AC Input) and powered it up again.  NOW, with nothing cconnected to the 12v and 5v terminals, I'm getting the correct voltages (12 and 5 respectively)

So, is this normal?  I expected that I'd get 12v and 5v readings with everything attached, but I did not (I got 4v and 1.6v) but with all disconnected, I'm getting the correct readings.  

Is this a result of:
A PS problem? If so, anything in particular pop to mind?
or a problem elsewhere in the cab perhaps?
Thanks

[paigeoliver]

Thats a power supply problem, I have an AR 3 board that does the same thing. Tests fine with no load, and drops to minimal voltages with load.

If it is a game with a normal switching power supply, then you can USUALLY replace it with a PC power supply. Most boards are fine with them, although you can forget anything from ATARI that had an AR board in it.

The downside to using PC power supplies is that they are non-adjustable, and some boards are REALLY picky about voltages (pickiest I have ever seen is super strike, which has only a .1 volt window that the ball sensors work properly in).

[Matt Berry]

A couple of things could be happening. First something may be grounding out, this could be a wire that is making a connection to ground or a componet has failed and is making the connection to ground. Check to make sure none of the wires have been damaged, or are exposed look for componets that smell funny or looked burnt. You can always disconnect wires and check the voltage when a new area is reconnected until you find the problem (make sure the common or "-" neg side stays connected. The second possibility is that the power supply can't supply the proper voltage when it is under load. Power supplies are pretty cheap with a little research. A computer power supply is a little more difficult to connect up. First off if it is a no name brand it probably won't provide stable power. I'd also look at the maximum amperage ratings on each rail. Computer power supplies (older) need to be under load when fired up or they will fry - You will also have to find the pinout for the MB plug so that you can connect a switch / Jumper to even get it to power up. All said you'd be better off buying a new power supply also remember if a componet failed or if something shorted out, it could have damaged your current power supply and when you put in the new one it could suffer the same fate  

[quarterback]

Thanks for the replies.  I decided to take-the-plunge and was just coming back to report my success!  

I used one (of many) old PC power supplies in my basement and some old speaker wire to rig this baby up.  Not only does the power supply work, I can now confirm that the monitor works as well (which was the whole reason I was trying to do this in the first place)

So, now that I know I have a working 19" arcade monitor, I've got to figure out the rest of my setup.  My plan at this point is to buy the JPAC and try to run my PC's VGA signal through it, although I'm not sure what the success rate is for that setup.  I guess I need to figure out if my video card can output 15khz.

As far as tracking down the voltage-drop problem, it's probably not worth the effort since I'm not going to actually use this power supply for long.  I just needed to get the game powered up so I could see if the monitor even worked.

[paigeoliver]

Just spend the extra bucks and get an arcadevga. I have done it every which way, and can now say with confidence just to get the arcadevga and jpac don't waste your time with anything else. Matter of fact I now even reccomend JPACs to people who aren't even using arcade monitors. Using a JAMMA harness is a great way to wire things up.

You can see if a monitor works without a gameboard or power supply. Just unhook the power from the power supply and power up the cabinet and look for glow on the neck, if you have glow then the monitor works, although it might need a capping or other minor repair (which is easy).