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Papahyooie
05-10-2010, 09:28 PM
I know this is kind of hardware related, but over at TPU there isn't any section (that I saw) specifically for audio equipment... I'll probably post something in general hardware just to get a bigger user base's opinion.

My father gave me his Sony home theatre system that he just replaced because there is a low level hum that is almost always present. When you turn the volume up, the music overpowers the hum, but with the volume low, you can still hear it. I'm sure it's some kind of interference, but I can't seem to find out what.

Things I've already tried:

Moving the unit (radio/power interference from outside?)
Different outlets (dirty power?)
Rerouting interior power cables (power cables next to signal cables causing hum?)
Switching signal sources, moving speaker wires around to different connectors, switching input methods (surround sound, etc) and general troubleshooting.
Looked at the boards for obvious problems, bugs, bulging caps, loose connectors, etc.

So far, no dice. Some more info:

The hum seems to be lessened on certain inputs (phono and FM radio are lower than CD player for instance)
The amp has two speaker "rails" (dont know what else to call them) A and B. B seems to have a little bit less hum.
It seems to have a little less hum on the surround modes, and moreover, a little less hum on specific types (dolby mode has less hum than simulated mode for instance) but I'm sure that just has something to do with the different sound configurations lessening it and not an actual reduction in the interference.
It has several power plugs in the back for the other componants (cd player, phono, FM radio, Tape deck) but unplugging those and using wall outlets does nothing to lessen the hum. I'm fairly confident it's not an outside source of interference.

Anyone got any ideas? I'm usually good with the basic stuff like above, but this one has me stumped.

JC316
05-10-2010, 10:00 PM
Could be a capacitor going bad in the unit. Otherwise, I say it's from the power source.

dr emulator (madmax)
05-10-2010, 10:10 PM
i agree could be the units drawing more power than the rectifying circuit can handle creating mains transients or hum
and yes it's more than likely change capacitor time

Papahyooie
05-10-2010, 10:43 PM
I don't see any caps bulging or leaking. How would I go about finding which one to replace. Surely not every one? There's like 200 of em lol.

JC316
05-10-2010, 11:31 PM
Look at the big ones near the heatsink looking thing. Listen closely to them.

Papahyooie
05-10-2010, 11:50 PM
I took a look at them, they didnt seem to be messed up. I didn't exactly listen to them though. Would they be whining or something?

Also they're massive, like coke can sized...

theJesus
05-11-2010, 12:09 AM
Also they're massive, like coke can sized...
Take a sip from one. If it tastes like coke, it's good; if it tastes like pepsi, change it.

Papahyooie
05-11-2010, 12:25 AM
Take a sip from one. If it tastes like coke, it's good; if it tastes like pepsi, change it.

What, no "that's what she said" ? I commend you for taking the high road, sir. Well done.

theJesus
05-11-2010, 12:39 AM
What, no "that's what she said" ? I commend you for taking the high road, sir. Well done.
It was a testament to my increased lack of proper brain functioning lately. The thought never even occurred to me.

JC316
05-11-2010, 01:26 AM
They usually hiss or bubble. Like a leaky tire, sometimes they can be difficult to hear.

Papahyooie
05-11-2010, 01:53 AM
Oki, well I'll take a closer look at those tonight. I really would like to get it down to at least a minimum, as its an awesome system, something I couldn't even come close to affording at the moment, and would make an awesome match for the new speakers I just got.

dr emulator (madmax)
05-11-2010, 11:33 AM
look and listen after it's been on a while (switch it off first) as i remember a cb's valve power amps capacitor blowing up and going in my eye :eek: now that scared the shxx out of me

Papahyooie
05-11-2010, 09:34 PM
Well sticking your ear next to exposed electronic equipment always has stupid written all over it, but I never was very smart when it came to that... You wouldn't believe the shock I got from my rear-projection TV's power supply while trying to plug the cable into the CRT... literally made me piss my pants, no joke.

However, I listened to them last night and they don't seem to make any noise that I can discern.

JC316
05-11-2010, 11:00 PM
Ok, try this. Plug it in, turn the volume up a bit and then flick a ceiling fan on and off. See if a popping noise comes through. Could be your power.

Wile E
05-12-2010, 05:49 AM
Most audio hum in an AC power environment is poor grounding. Is it a 3 prong plug? If so, check to make sure the ground is still intact on both ends of the cord.

You can also run a ground wire from a chassis screw to the center screw of your outlet (the one that holds the cover on).