"JohnC" wrote in message
.. .


That's actually a slightly odd set of symptoms. The fact that it is
altered by the volume control, indicates that the hum is getting in
'front end', which is usually down to a grounding issue on the input
signal cable or whatever. However, that being the case, the hum would
not normally be expected to be present on all inputs (and presumably
on both channels ?). OTOH, a power supply fault that is causing hum,
will not usually be affected by the volume control.

I suppose it is possible that one of the electrolytics in the power
supply is getting poor - it is certainly old enough to have electro
trouble - but it is my experience that these older types rarely fail,
especially if they *have* been going for 30 odd years without trouble.
It would, I think though, still be my first move to check them either
for ESR, or better, for ripple present on them. If you don't have a
'scope, you could get an idea of the ripple level by measuring the
voltage across them, with the meter set to an AC volts range. You
should struggle to get any reading much above zero. After that, I
would be looking at a bad regulator transistor, such as that one at
the left hand side, bolted down under the transformer. I've known
rails that have gone high from a short or leaky regulator, cause such
disturbance to preamps.

Arfa


Or a ground loop - is cable TV, outside antenna or a computer connected
to the HK in any way?

Mark Z.


Thank you all for the responses. I apologize for leaving the post
hanging. I have been out of town and unable to post a reply.

Here are some items that I have done along with some additional
information:

1. The unit is not hooked up to a cable TV, outside antennae or
computer. It is only hooked up to indoor rabbit ears antennae, tuner,
and speakers. I do not suspect a ground loop.

2. I disconnected everything, antennae, speakers, and tuner. Listening
through headphones the hum is still present.

3. I shorted each RCA input to ground. Hum still present.

4. The hum is inaudible with the volume knob turned all the way down.
The hum is present on both channels. The hum showed up suddenly.

5. I removed the case and bottom and inspected all grey capacitors.
There is no hint of corrosion or a bulge in the end seals.

6. I failed to mention in my original post that for years the volume
(pot?) emitted audible static when the volume was adjusted. Somebody
mentioned that this should probably be replaced. Probably long overdue
for replacement and perhaps the source of the new pesky hum?

John

Someone may have already suggested this, but do look at the output of any
voltage regulators. Could be a dried up capacitor near one of them. I
just looked over at the Harman dealer site - no service data there. I'll
see if I have a manual at work and post back.


Mark Z.


I sprayed cleaner in the volume control, hum still present. Something
else.. the hum is audible no matter what input is selected from the input
switch, FM, AM, Phono, tape/aux. But there is a Monitor switch and when
switched from Source to Monitor, the hum ceases.

John C.


That is odd... maybe a wiring or corrosion problem at the rear of the unit.

I looked at work - no service manual on a 230A, just a 230E which is
COMPLETELY different.


Mark Z.