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I've got a brand new hum (pioneer sx 750)

Moth R. Superior

Moth R. Superior

Active Member
Hello all, So, I've got a new hum goin' on.
it almost sounds like a power sort of hum (as opposed to grounding)
it shows up on everything, AM, FM, AUX, PHONO...
any ideas?
thank you in advance!
-Mike
 
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Moth R. Superior said:
Hello all, So, I've got a new hum goin' on.
it almost sounds like a power sort of hum (as opposed to grounding)
it shows up on everything, AM, FM, AUX, PHONO...
Click to expand...
Do you get it with all sources unplugged from the receiver, with the only connections to the unit being the power cord and the speakers?

If so, you might have failing power supply filter capacitors.
 
Moth R. Superior said:
NO! it stays the same!
Click to expand...
Most likely one or both of the pair of 15k mfd filter caps have failed. Whilst it's possible to replace just the failed caps -- assuming that's the cause of the problem -- given the age of the unit it should be recapped, i.e., all electrolytic capacitors replaced. However, the hum might also be caused by a shorted rectifier diode, but if so the failed rectifier(s) will need replacement, and it should be fully recapped anyway for best performance and longevity.
 
Constant hum (independent of volume control) is usually power supply ripple (capacitors). Do you hear it at zero volume? If it is power supply, one would expect that you would.
Is the hum 60 Hz or 120 Hz? I am sure you can find samples of both on line and judge for yourself.

Here're a couple:

120 Hz:

60 Hz:

Generally speaking, open ground will give you 60 Hz hum; p/s ripple can be 120 Hz -- but, remember: all generalizations are false, including this one.
:)
 
Moth R. Superior said:
thanks guys. is the unit worth re-capping?
Should I attempt it myself, or hire someone to do it for me?
Click to expand...
Are you good with a soldering iron?

It's not going to get better by itself, and if you're handy with tools and have some knowledge of electrical principles or electronics, it's a relatively straightforward job.

Do you have a multimeter?

A good start would be to use it to check the rectifier diodes for shorts or opens.
 
I'll tell you what, I can't get into it tonight, but I'm gonna give it a whirl .
I may be asking for advise in the near future! :thumbsup:;)
(oh who am I kidding? I MOST DEFINITELY WILL be turning to you guys for help!)
 
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