did i just kill my power supply?

mrjason

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I saw a couple threads here about using a multimeter to check voltages at the jamma edge connector.

I have my multimeter set to 20V DC mode.

My multimeter has a black lead plugged into a port called COM (common ground?), and red into one with all kinds of power symbols.

I put black with black, red with red, touching the inside of the jamma harness connector, and got a reading of 3.5v fairly steady (this without ever adjusting the pot on the back of the power supply).

Then I adjusted the pot on the back (a very minimal amount), this made the power supply's fan increase in speed but no sign of changing voltage, so i turned it back down to the "original fan speed".

I know nothing about electricity, so like an idiot i thought maybe my multimeter leads are backwards, so I plugged red with black and black with red on the jamma connector, the power supply instantly turned off. I didn't hear a pop, didnt hear anything funny, it just turned off.

Turning the machines power on/off does not bring the power supply fan back to life.

Is it dead? Did I just do something *really* bad, and if so, will just the power supply be fried, or is the jamma harness likely screwed up too or other parts like monitor etc..??

For reference this is an open ice 2 on 2 machine. Was trying to make sure my voltage was 5.2v for a test run of a new blitz board I received.

Also, is 3.6v a good reading at all? I've been running games on this thing (several PCBs) for months without issue, I can't see how 3.6v would be in the acceptable range to run something like my good blitz 99 board. (my multimeter is a $20 meter from fry's, by electro-tek). Testing a 9V battery before and after possibly killing the power supply reads 9.3v consistently..
 
Measuring voltage with the leads reversed is absolutely fine, you'll simply get a reading of say -5v instead of 5v. Either you've slipped and shorted the power supply out, or it has coincedentally died while you've been measuring.

Either way if it was only outputting 3.5v it needs to be replaced. 5.2v is too high as well. I suggest always run a board at 5.1v unless you are having problems and find that increasing the voltage resolves them.
 
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I can't see how those boards were running at 3.5 or 3.6v -- doesn't make sense. Somehow you were measuring something wrong.

Is there a circuit breaker on the power supply that tripped? Or a fuse you can check? I wouldn't freak out about it; probably just something with the power supply.
 
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It seems like the power supply fan turns off after a minute or two if the jamma connector isnt connected up to a pcb (It wasnt plugged into any boards for these tests.)

A few minutes later turning it on, the fan came back on. I had some trouble getting the multimeter to read correctly, don't know if the multimeter itself is going to pieces or what, but it seemed if I didn't catch the 5 volt read quickly after power would turn on, I wouldn't get it at all.

One followup question, I turned it up to 5.2 to test this power hungry board and that worked a bit better for that one (though still no POST yatta yatta). What should I leave the voltage at for normal non-power hungry boards, is 5.1 cool?
 
It seems like the power supply fan turns off after a minute or two if the jamma connector isnt connected up to a pcb (It wasnt plugged into any boards for these tests.)

A few minutes later turning it on, the fan came back on. I had some trouble getting the multimeter to read correctly, don't know if the multimeter itself is going to pieces or what, but it seemed if I didn't catch the 5 volt read quickly after power would turn on, I wouldn't get it at all.

One followup question, I turned it up to 5.2 to test this power hungry board and that worked a bit better for that one (though still no POST yatta yatta). What should I leave the voltage at for normal non-power hungry boards, is 5.1 cool?

Yeah, the ps is expecting a load when it's on. I wouldn't keep putting it in a situation where it doesn't have one.

Between 5.0 and 5.1 should be good for most things.
 
If anything you would damage the motherboard, not the jamma connector or the monitor. There is a fuse in the PS that can blow. What kind of meter is it ?
Are you sure you are on the right spots on the motherboard to check the +5
 
Yes 5.1 is fine.

Take my advice, or at least think about it. Throw that meter in the trash.

Your old board was not running at 3.6 volts, it would have never booted. The meter is giving you false readings. A cheap meter, when the battery starts dying will give you FUCKED UP readings, you'll never be able to trust it.

Imagine if you turned the power supply up 1.5 volts over the 3.6... and ended up REALLY sending 6.5 volts to every chip on your $100 or $200 pcb.

I used to use those little cheap meters, but they probably cost me hundreds of dollars in damaged pcb's.


If you get a Fluke meter (get a used one, they're cheaper!)... when the battery starts dying, that thing will give you a solid, dead on reading right up until the point it won't turn on anymore. Other people on the board might be able to suggest a good cheaper one too, but I wouldn't trust that one you've got, because as you've seen the readings change when the battery is low.
 
Thanks for the multimeter suggestion. My POS was like $20, definitely not the price range of these flukes I see on amazon :)

The thing I dont get about the readings I was getting (probably due to the "expecting connection on boot") is that every time I've used this meter on like a car battery or AA or 9V battery I've never had a problem reading something that at least made sense. Seeing it hold steady at 3.5 was strange, but then when I pulled it out and put it back in the jamma harness I got nothing (probably again b/c the power supply expected a connection and did something when that was lost..?).

I was worried about turning the power to something like 6.5 without knowing while a PCB was plugged in, so thats why I was testing with it unplugged, for future I'll make sure I can pull power right off the PCB before I fiddle with the voltage.
 
Oh also, the multimeter is electro tek. Probably not a good sign that I can't find it on frys site, amazon, or even on google, and I only bought it about 3 years back :/
 
Yeah for real. You might have saved that board you were about to try, lol.

If your power supply is one of those big silver boxes, they're really finicky. They like to turn off when you adjust them, and won't come back on for a few minutes, etc. It's probably got some issues or it's on it's way out.
 
Oh also, the multimeter is electro tek. Probably not a good sign that I can't find it on frys site, amazon, or even on google, and I only bought it about 3 years back :/

Sounds like you should try a new 9v battery in there and you'd probably start getting real readings again. But as it was pointed out, better DMMs will either give you accurate readings right to the end or at will at least tell you the battery is low so you can change it. If you do replace the battery you should check the voltage on the 9v battery in your meter that was giving you trouble and tell us what the voltage was. :)

I have an ultra-cheapy one I got at Fry's years ago and it is really accurate but the rotary dial drove me a bit nuts -- you have to be really careful to click it into the correct spot to get a proper reading. I finally went and bought an Extech meter for about $50 that I've been really happy with.
 
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I'd like to recommend the Uni-T multimeters. I have one similar to this:

China_UNI_T_Digital_Multimeter201081917163510.jpg


I also have a nice Dick Smith one which has an automatic backlight and does up to 20A, but they don't sell them anymore.
 
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