Poof! What was that cloud of smoke in my Exceleena?

[shmup-o]

Ok, I picked up some boards from my PO Box at lunch and headed home to drop them off real quick. Decided I had time to test them real quick and with one of them the Exceleena made a weird screeching noise and then a poof of smoke came off the power supply. I took the PCB out and put in a working PCB and the Exceleena started up fine.

I almost had a heart attack, but I think everything is ok - does anyone know what the heck could've happened?

[ZOM]

Most likely a blown cap. Your board should be perfectly save, I think. If you're not knowledgeable enough to replace the bad caps, I'd suggest you toss that PSU. Otherwise, if you know someone with basic soldering skills, replacing the caps shouldn't be a problem.

Other than that, there's a possibility that a short was caused somewhere and more components were damaged. (less common, but happens)

[shmup-o]

Most likely a blown cap. Your board should be perfectly save, I think. If you're not knowledgeable enough to replace the bad caps, I'd suggest you toss that PSU. Otherwise, if you know someone with basic soldering skills, replacing the caps shouldn't be a problem.

Other than that, there's a possibility that a short was caused somewhere and more components were damaged. (less common, but happens)

Does this mean I should not be using my cab until I fix or replace the power supply?

[ZOM]

If you have any means(multimeter) to check on voltages your PSU is outputting, you could test if they're alright (+5v, +12v, -5v, etc) before trying to hook anything else on it. Don't want to fry any further boards you hook on it...

Can you check for bulged caps and/or burned components & take a pic of the PSU-board?

[brentsg]

I did this once because a wire on my JAMMA harness became frayed a bit and made contact with the un-grounded cab.

Lessons learned on many fronts for me there, especially since I had my head up in the cab when it blew.

[rugdoctor]

... since I had my head up in the cab when it blew.

Jezus...you just described my worst fear when working on the cab.

[caldwert]

Matskat on here can attest to me inhaling a lung full of magic smoke myself when a cap blew on a Quartet board I was going to sell him. Plugged it in, and didn't get anything on the screen, was reaching in the cab to turn it off, and bam got blindsided by the foulest smoke cloud ever. One of the 25 year old cap's let go on the board. Scared the shit out of me.

[shmup-o]

If you have any means(multimeter) to check on voltages your PSU is outputting, you could test if they're alright (+5v, +12v, -5v, etc) before trying to hook anything else on it. Don't want to fry any further boards you hook on it...

Can you check for bulged caps and/or burned components & take a pic of the PSU-board?

I'll try to find time to check out the PSU board and take a picture. I just found a multimeter in my pile o' tools, I have no clue how to use it though. Good time to learn!

[ZOM]

Good time to learn!

You won't regret it!

[antron]

do the capacitors look any different after they "blow"?

I have a Truxton board that did this, but I cannot find abything visualy wrong with it. Should I replace all the caps?

[ZOM]

^If we're talking electrolytic caps, sometimes they form a "bulge" on the top, separating the four sections. (This also happens if a bad cap is leaking)
It's also possible that the top looks perfectly fine but they get bulged on the bottom side, which might be a bit harder to spot. Mind you, I'm not an expert on this, just seen my fair share of damaged components.

EDIT: Just looked at a pic of a Truxton PCB, seems there's just a bunch of axial caps on those boards. I'd say it shouldn't take too much work to replace them and it doesn't do any harm replacing them eitherway. I'd also take a look at the diodes there, checking with a multimeter if they pass current just from their intended direction.
If still nothing goes, an other possibility are those transistors near the Jamma pins. The problem is you never know if the damage also killed some ICs...

[shmup-o]

I'm pretty sure the cap is bad, the one right next to the molex plug is bulging. That is also where I saw the puff of smoke as well (I thought it was from the molex plug originally, but from the front of the cab the cap is right behind it).

Pic

I have a few more pics of the board as well, all shot with a camera phone with the power supply board still in the cab. I ran out of time trying to take it out, can post better pics later.

Can someone point me to a good guide on using a multimeter?

Thanks for the help!!

[ZOM]

Yeah, that's definitely one I'd replace. The rest seems to look ok, at first glance.

As for the multimeter, they come in all flavours but for this kind of work a basic one is more than enough.
As for using it, there should be plenty of guides on the net - a quick search googling "using a multimeter" gave the following result which is already easy enough to understand, I think: http://www.wikihow.com/Use-a-Multimeter
Also, youtube should be full of informative videos about the topic.

EDIT: I almost forgot the most important: inform yourself well before sticking those probes in the wrong places! Note that (obviously) the PSU needs to be running to measure the molex plug's various voltage outputs; don't touch any of the components while the thing is running. Electricity deserves your utmost respect.

[shmup-o]

I watched a tutorial (three to be exact ) and checked the voltages at the jamma edge connector. I got the following readouts:

12V: 11.3
-5V: -6.64
5V: 5.22
5V: 5.22

Then I checked the PCB which blew the cap in the first place and it came up just fine- weird. Maybe disconnecting and reconnecting everything helped out?

Let me know if anything looks out of place - the 5Vs look like they should be fine, the 12V might be an issue, but the -5V seems really off.

Thanks for your help on this!!

[ZOM]

I'm glad to be of some help!

AFAIK the ideal tolerance on PSU voltage rails are +/-5% for positive voltages and +/-10% for negative. The only weird one is indeed that -5v running @ -6.64, but it's still acceptable, I think. (if anyone reading this knows better, please correct me)

I really don't know how that "unhealthy" cap is related to the boards output pins, but everything seems fine so far. I wouldn't be too worried about the -5v since few games use it and if they do it's mostly for sound.

[shmup-o]

I'm glad to be of some help!

AFAIK the ideal tolerance on PSU voltage rails are +/-5% for positive voltages and +/-10% for negative. The only weird one is indeed that -5v running @ -6.64, but it's still acceptable, I think. (if anyone reading this knows better, please correct me)

I really don't know how that "unhealthy" cap is related to the boards output pins, but everything seems fine so far. I wouldn't be too worried about the -5v since few games use it and if they do it's mostly for sound.

Thanks again ZOM - I think I'll take the concern to KLOV and/or Arcade Otaku for advice as well. I have issues with two -5v volume games, but it could just be a coincidence.