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Measuring A Capacitor

I have a preamp (NAD 1155) that has a hum problem. It started when I got a new turntable, so I thought it was a TT grounding problem. But no... The preamp's phono section hums every time it is selected. Even if there is no phono present. All the other inputs are dead quiet.

Anyway, a fellow 'goner thought it is a capacitor that's going 'round the bend. I'm willing to take my volt/ohm meter, and find the offending component, and replace it. All I know about capacitors is that they are measured in picofarads, and they discharge their energy in bursts, when it's requested.

Any help in this regard is much appreciated. I have a mountain of vinyl waiting to be played.

TIA

Lee
licoricepizza
licoricepizza OP
48 posts
 
The IC to every input didn't work, so now I'm on to shorting the ICs. We'll see... Do I need to turn anything off while I'm doing this? I'd hate to damage my Vandersteens while performing this. Also, I have a question. Someone thought a cap is going bad, hence the buzzing. If a component like that is bad, shouldn't the buzzing be present constantly? For me, there are times when the buzzing is totally absent.
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almarg
9,670 posts
 
Do I need to turn anything off while I'm doing this?

Yes, definitely, although it might be less critical if a different input were selected while you applied or removed the short. But that would be bad practice anyway.

If a component like that is bad, shouldn't the buzzing be present constantly?

Probably, but not necessarily. The component could be marginal or intermittent.

Regards,
-- Al
licoricepizza OP
48 posts
 
In order to be perfectly clear, I:

Turn the stereo off
Put the shorted IC in place
Make sure Phono is selected as the input
Turn the stereo back on
Turn my house into a smoldering pile ashes (just kidding)
Listen for the dreaded hum on the phono input

Thanks for all your help.

Lee
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almarg
9,670 posts
 
Yes!

-- Al
herman
2,252 posts
 
Sorry I wasn't clear. I meant take one interconnect and plug it into the right channel input of the phono and the other end of that same wire into the left input.

If it were mine I would short the input with the system powered up. I can't imagine a scenario where shorting an input would cause noise on the output but I suppose it won't hurt to turn it off first.

Good luck
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