Sound experts: what's that buzz?

[Arcade Antics]

Have a Klax cabaret that was 100% AOK before moving it; after a bumpy ride, it's buzzing loudly. I checked the obvious things - sound self test, ground wires that may have come loose, loose connections, etc. and no dice. All the sounds work properly too, it's just got that loud buzz over the top of everything.

I suspected possible interference from the monitor, but that might not be the case. Any ideas?

[SuperGunGuru]

I had a friend of mine suggest that a sound buzz might be caused from the marquee light. Not sure if your cab has a light for the marquee since it's a mini though.

[FABombjoy]

Basically, you just want to turn off/disconnect as much as possible until you reveal the cause. Does the buzz ever change in tone/pitch at all?

View the basement arcade:
http://www.msu.edu/~miekkawi/basementarcade.jpg

Basement arcade? MSU? This isn't near E. Lansing is it? I work at MSU.

[Arcade Antics]

Basically, you just want to turn off/disconnect as much as possible until you reveal the cause. Does the buzz ever change in tone/pitch at all?

View the basement arcade:
http://www.msu.edu/~miekkawi/basementarcade.jpg

Basement arcade? MSU? This isn't near E. Lansing is it? I work at MSU.

I tried disconnecting the monitor and still got the buzz; it's not changing in tone, but when the game is in attract mode and it switches between screens, there's a tiny dropout in the buzz when the screens switch over.

[DogP]

Have you tried turning the volume pot? When you turn the sound up, does the buzz get louder, or stay the same? If it gets louder, there's a problem before the amp, check to make sure screws, wires, etc didn't fall behind the PCB and short stuff. If you pull the PCB(s), you should check to make sure that all the solder joints are good, and resolder any that look like they might be old/cracked.

If you change the volume and the buzz stays the same, the problem is after the amp, so you should check to make sure that none of the wires going to the speakers have stripped sheathing and grounding out, or maybe a problem with, or right at the amp.

You should also inspect the volume pot. Make sure it's not cracked or dirty... I've had a cracked pot cause buzz and popping noise through my speakers.

Usually rough moving doesn't cause any real damage to the PCBs and stuff, but causes problems with broken solder joints and loose wires.

DogP

[Arcade Antics]

Have you tried turning the volume pot? When you turn the sound up, does the buzz get louder, or stay the same? If it gets louder, there's a problem before the amp, check to make sure screws, wires, etc didn't fall behind the PCB and short stuff. If you pull the PCB(s), you should check to make sure that all the solder joints are good, and resolder any that look like they might be old/cracked.

Ah! Good call, that's part of the description I forgot to mention. It does get louder as the volume is increased. Since I was presuming the problem wasn't board related, I haven't even pulled the PCB yet. I'll do that tonight and keep you posted.

You should also inspect the volume pot. Make sure it's not cracked or dirty... I've had a cracked pot cause buzz and popping noise through my speakers.

Usually rough moving doesn't cause any real damage to the PCBs and stuff, but causes problems with broken solder joints and loose wires.

Thanks for the helpful pointers! I'll get a good look at the pot and the board later on, hopefully it's something simple like reflowing the solder.

[98PaceCar]

Before you start reflowing solder, take a look at the fuses and the ac filter block in the bottom of the cab. I'd suspect a problem with the ac line before board problems.

[SuperGunGuru]

Basically, you just want to turn off/disconnect as much as possible until you reveal the cause. Does the buzz ever change in tone/pitch at all?

View the basement arcade:
http://www.msu.edu/~miekkawi/basementarcade.jpg

Basement arcade? MSU? This isn't near E. Lansing is it? I work at MSU.

Not exactly. It's at home which is about 40 mins from MSU. I actually commute to campus (I lived on campus but didn't care to return). What do you do at MSU? I'm a senior this year.

[Arcade Antics]

Update: it's not the fuses, the pot, and probably not the board. I did see a weird spot near one of the edge connector pins that looked like it may have once had a spot of solder on it but it broke off, but at this point, I don't want to drop some solder down there and make things worse.

Guess the next step is to check the ac block; just have to pick up a new multimeter first.

[chadtower]

Did you do the simple things like reseating all of the edge connectors and checking the wire connections? That could easily be caused by a jostled connector no longer being solidly connected. In fact it's likely caused by that.

[Arcade Antics]

Did you do the simple things like reseating all of the edge connectors and checking the wire connections? That could easily be caused by a jostled connector no longer being solidly connected. In fact it's likely caused by that.

Yup - I have a tendency to be lazy, so that's always the first thing I do. I'll take a picture of the PCB edge connector to get a close up of the mysterious solder spot I mentioned up above and post it here. I'm wondering more and more if it had always looked like that, or if, like you mentioned, it got jostled and knocked off a small (but necessary) dot of solder.

[chadtower]

Knocked off a small dot of solder? That doesn't happen. If that's not actually soldered on there you should be able to just flick it off with a finger.

Check the continuity of those connector pins, connectors get flaky when they get older.

[Arcade Antics]

Knocked off a small dot of solder? That doesn't happen. If that's not actually soldered on there you should be able to just flick it off with a finger.

Check the continuity of those connector pins, connectors get flaky when they get older.

Yeah - this one is only 15 years old though and it's in really nice shape all around.

Sorry for my bad description of the weird looking "maybe solder" spot. It looks like a small crater, as if there was once a piece of solder on the board in this spot. You know how sometimes you'll find a spot that's soldered, but it doesn't really go anywhere - it's just filled in to complete a circuit? It's sort of like that, but it looks like a hard jostle could have (maybe!) knocked the solder point off. If, indeed, there was a solder point there to begin with. Might make more (or les) sense once I grab a pic of it.

[chadtower]

Yeah - this one is only 15 years old though and it's in really nice shape all around.

That's about 10 years past the expected lifespan of your average PCB connector.

[Arcade Antics]

Well, I'm a dumbass, but at least I'm consistent.

DogP is the winner so far - it turns out that the board IS the issue.

I was typing a response to Chad earlier about the simplest stuff when it dawned on me - Klax is a JAMMA board.

Duh! I told you guys I'm a dumbass. Anyway, I swapped out a different board and lo and behold - no buzz at all. The simplest thing of all, and I waited until now to do it.

So, I've got the buzzing narrowed down to the board. None of the solder joints appear to be bad, none of the wires appear to be bad, and I've reseated all the roms.

Any guestimates as to where to head next? All I can think of is to reflow all the solder, but that'll take all day, so any help in narrowing places to start is appreciated.

And all the responses so far are GREATLY appreciated. Thanks guys.

[98PaceCar]

Check your voltages at the jamma connector. Maybe the 5v rail is a little weak. I've had boards that act differently in the same cab before. Past that, look for the section on your board that has a bunch of caps and transistors. It'll most likely be your sound section. Also, look to see if there's a volume pot on the board.

[Arcade Antics]

Check your voltages at the jamma connector. Maybe the 5v rail is a little weak. I've had boards that act differently in the same cab before. Past that, look for the section on your board that has a bunch of caps and transistors. It'll most likely be your sound section. Also, look to see if there's a volume pot on the board.

Yeah - the volume pot is on the board. It's one of the first things I tried reflowing the solder on.

No dice.

I kept picking different caps on the board to reflow while intermittently stopping to plug in the board. At some point I must have reflowed the proper cap and/or transistor, because it's back to 100% perfection now.

THANKS again to everyone for all your help in troubleshooting this one.

[DogP]

WOOT! Congrats...

DogP