hifi engine

Dealing with an inherent hum regardless of volume or source selection

I have a VSX D1S Pioneer reciever which I recently acquired and had it running my Technics turntable and AL1200 spearker.

Recently I noticed a hum regardless of the volume and source selection. I assume it is related to the power transformer and potentially a faulty Capacitor but not sue where to start looking to eliminated this annoying hum.

Can anyone provide some insight into the cause and possible corrective action. It is not a grounding issue with Turntable as I have a god ground connection and as stated it happens regardless whether the turntable is connected or if it is switched to CD,tape etc.
Thanks



Re: Dealing with an inherent hum regardless of volume or ...

I have a Sansui 2000 receiver that has a hiss at no volume on all functions It is concealed when the volume is increased. Where should I look? I have the service manual. If a capacitor dries out will it not pass AC or will it pass DC? I have the right dc voltage on the large filter cap but there is 60 vac there?

Re: Dealing with an inherent hum regardless of volume or ...

I don't know that particular Pioneer model but I have troubleshot many hum problems and I would suggest : remove any & all external unit's wires both audio and AC from your
unit under test. then reverify if you have the hum through the speakers and/or headphones. if still there, engage each switch or control one at a time see if anything
consistently affects the hum. if not, the higher choices on a list of possible causes might be power supply filter capacitors or some horrendous ground problem. I used an o'scope
(ac input) to view the ripple on the capacitors to find the defective one. A close visual
inspection and or flexing the circuit boards and wire cables cautiously with an insulated
probe (like a pencil with eraser) might get you to an area where an ohmeter can help pinpoint the exact fault in a grounding based problem.
another possibilty is a defect in the power amp electronics. a quick test is to measure
to see if there's any DC voltage on the + speaker output terminal. optimal should be 0 DC but realistically there
shouldn't be anything much above maybe 20 or 50 millivolts. if you see higher DC
than that here, you've possibly got complex electronic circuit problems.
I haven't done this in a long time but it's the way I would troubleshoot your problem. hope it helps.
if you don't have access to test equipment then try a slow careful visual inspection
of the circuit boards looking for any cracks or bad solder joints.

Re: Dealing with an inherent hum regardless of volume or ...

Does it come through the speakers? If it is power supply related then any power source to any amplifier or preamplifier could be the source.

Re: Dealing with an inherent hum regardless of volume or ...

Thanks for your interest, yes it does come through the speaker and headphones. So you suggest looking at power supply caps to each amp and preamp.

Re: Dealing with an inherent hum regardless of volume or ...

Most hum problems are caused by the filter caps in the power supply section. It may or may not be the larger caps; there may be a low voltage regulated supply feed with smaller sized caps that can cause the same hum issue. If you have a scope available, looking at the ac ripple voltage on all of the dc power supply sources should quickly identify which one is causing your problem. Any supply over about 50mv ac ripple would be suspect.