Pioneer VSX-920K Hum

[UND312DOG]

All,

I've recently been getting a hum/buzz through my home theatre system. When I installed it early last year everything was fine, no noise. Recently I have noticed a hum. Originally I thought it was a ground loop. So I did an isolation test. No change. I also tried a new PowerPoint via a extension cord with everything connected from my home theatre to it. Noise still there.

The loudness of the hum is becoming unbearable to a point where I have to turn the volume up to drown out the hum. Which is no good at night with the bub asleep.

I have also noticed sometimes when I turn my receiver off and leave it off for a minute or so. When I switch it back on the hum is very slight and barely noticeable, unless I put my ear to the speaker.

With all this in mind I believe there is a fault somewhere in the VSX-920k, something inside is causing this hum through the speakers.

Thoughts?

[budm]

Re: Pioneer VSX-920K Hum

Do you still get hum if you remove all the input signal cables, just have the amp and the speakers only?

[tibimakai]

Re: Pioneer VSX-920K Hum

I remember a Youtube video with a similar issue(different receiver though) and it was a bad capacitor.
Here it is:
http://www.youtube.com/watch?v=-4b1PSy2TSQ

[UND312DOG]

Re: Pioneer VSX-920K Hum

Yep. I have isolated individual inputs. Changed inputs via the amp. Still a hum. Sometimes it's there. Then sometimes not. I'm assuming its a problem with one of the components inside. Looking at that YouTube video it's sounds exactly like that. So probably a capacacitor. I will have to open it up and take a look at the board.

[UND312DOG]

Re: Pioneer VSX-920K Hum

Ok. Opened up the receiver. What a pain in the arse. Anyways, found 0 bad capacitors. I noticed that some of the ground screws seemed a little loose. So I put it all back together, connected it back up. Hum gone. Not sure why though. Maybe a loose cable, bad ground. Any ideas?

[budm]

Re: Pioneer VSX-920K Hum

If you at the bottom side of the boards, they use the board mounting screws and the ground pads around the board mounting holes for grounding, I usually solder piece or wires from those ground pads to the chassis so I do not have to tighten the screws in the future.
Glad you found the problem.

[UND312DOG]

Re: Pioneer VSX-920K Hum

Ok. So everything's been fine since my last post. Until two days ago when the hum returned. It driving me nuts. It's weird that it's been fine since May 2014 then suddenly returning again. I'm going to have to pull it apart and have another look. Ive being doing a bit of research and it seems most of time, the problem is a bad capacitor.

Any other ideas?

[UND312DOG]

Re: Pioneer VSX-920K Hum

To add. It's been humming all day. And has now stopped. Very weird indeed.

[R_J]

Re: Pioneer VSX-920K Hum

Maybe it does'nt know all the words so it hums I would take the cover off when it's humming and using a plastic or wooden stick, probe around looking for a poor connection somewhere on a board or a cable. It could be a poor solder connection somewhere on one of the boards.

[Longbow]

Re: Pioneer VSX-920K Hum

Originally I thought it was a ground loop.

If you made no changes to the system wiring, then why would a ground loop suddenly appear?

So I did an isolation test. No change.

You didn't describe what your isolation test was, and what it attempted to show. In other words, what did you isolate from what? The usual test is to remove all connectors and wires, leaving only the AC power cord, while listening with headphones. Also, it is good to specify whether you hear nice smooth 50/60 Hz hum, or rather an annoying buzz sound, which actually is not hum at all.

The loudness of the hum is becoming unbearable to a point where I have to turn the volume up to drown out the hum.

All channels have hum? All inputs have hum? Does the hum get louder when you turn up the volume control? If not, you don't have an amplifier problem.

I have also noticed sometimes when I turn my receiver off and leave it off for a minute or so. When I switch it back on the hum is very slight and barely noticeable.

...finally we're getting somewhere. That would mean the hum is actually coming from the unit itself and not being picked up from outside sources.

The next step is to check the individual inputs one by one using your switch-off method (above). If you get the same slow increase in noise or hum as the unit warms up, I recommend investing in a can of freeze spray. Carefully cooling different sections of the unit one at a time could isolate your trouble. At the moment, I'm betting on the DSP.

[UND312DOG]

Re: Pioneer VSX-920K Hum

Ok. Bringing up my old topic. The problem returned. Today I pulled the whole receiver apart. Took out all the cards. Tested the filter capacitors, all good. Powered it back up. Still humming. Even via the headphone. So I assumed it was a ground problem.

So I went through all the grounds and made sure whilst assembling it I checked every ground pad and ground. Plus anything that had a screw attached to the chassis. It's all back together and zero humming. So I'm guessing it was a ground on one of the cards to the chassis.

Kinda weird that this appeared out of the blue but I guess due to heat and expansion/contraction the contacts on one of the ground circuits wasn't 100%.