[modern] Radio Hum

Help!

Have just started noticing a hum coming from the radio, sounds like D second
octave above middle C. Does not occur if engine not running - then when
engine starts appears to delay for 1 or 2 seconds and the starts. Volume
control makes no difference. Is this Alternator diode going? Bad ground
somewhere? Radio going?

Thanks, Frank Towle
'91 Sov BRG 87K miles

Frank,
It sounds like you already came up with the possible problem areas,
but if its the alternator, you should hear the noise change pitch
with engine speed.

It could be a bad solder connection inside the radio…there are filters
on the dc input to the radio.
Antenna grounds, and so on.

Did you do anything/have anything done just before the noise started?
If you turn all the lights on, the rear window defroster, does the
voltmeter look ok, or is it putting out less power then it did?

As a guess, I would say its more likely a bypass problem rather than
a serious alternator problem…

Brett
1990 XJ6
…Date: Mon, 06 Dec 1999 00:21:47 -0500
From: Frank Towle ftowle@mediaone.net
Subject: [modern] Radio Hum
Sender: owner-modern@jag-lovers.org
To: modern@jag-lovers.org

Help!

Have just started noticing a hum coming from the radio, sounds like D second
octave above middle C. Does not occur if engine not running - then when
engine starts appears to delay for 1 or 2 seconds and the starts. Volume
control makes no difference. Is this Alternator diode going? Bad ground
somewhere? Radio going?

Thanks, Frank Towle
'91 Sov BRG 87K miles

Thanks for help Brett

Brett wrote…
It sounds like you already came up with the possible problem areas,
but if its the alternator, you should hear the noise change pitch
with engine speed.

No real change with engine speed. Does drop a little with all electrical
on.

It could be a bad solder connection inside the radio…there are filters
on the dc input to the radio.

Are filters inside radio or external (easier to get at ?)

Antenna grounds, and so on.

Did you do anything/have anything done just before the noise started?

Had removed and cleaned power antenna - noticed antenna lead was kind of
cobbled up, certianly not factory crimping, corrected best I could with no
diff in hum.

If you turn all the lights on, the rear window defroster, does the
voltmeter look ok, or is it putting out less power then it did?

Voltmeter looks ok. putting out 13.5 - then drops to 13. All electric on
putting out 14V+.

As a guess, I would say its more likely a bypass problem rather than
a serious alternator problem…

Brett
1990 XJ6

Date: Mon, 06 Dec 1999 00:21:47 -0500
From: Frank Towle <@Frank_Towle>
Subject: [modern] Radio Hum
Sender: owner-modern@jag-lovers.org
To: modern@jag-lovers.org

Help!

Have just started noticing a hum coming from the radio, sounds like D
second> octave above middle C. Does not occur if engine not running - then when
engine starts appears to delay for 1 or 2 seconds and the starts. Volume
control makes no difference. Is this Alternator diode going? Bad ground
somewhere? Radio going?

Thanks, Frank Towle
'91 Sov BRG 87K miles