Thank you all for your assistance and suggestions to help me with this
hum problem. I opened it up again today and removed the front too to
better inspect connections on the front panel. With the unit on, I
tapped all over the unit with a non-conductive tool. I was unable to
have any effect on the hum. I loosened and tightened many screws.
Especially those that appear to provide some grounding. No change. I
found no connections that appeared suspect.

I suppose the next step is to test the caps with an ESR meter. This is
probably beyond my ability and will involve the purchase of such a unit.
So I think I will button the unit up, and for now keep it on 'Monitor'
and use an external tuner on the monitor inputs. There is no hum when
using Monitor.

Yes this unit is a relic and in fact purchased by my wife new in the
early 70's. Perhaps not worth the service fee for repair, but it
provides a connection to the past so I'll keep in for her a bit longer.

Thanks again.

John



Was the hum only on the (FM) radio section? That would have narrowed it
down somewhat...

Mark Z.


Mark,
The hum is there for phono, AM, and FM - so all source inputs.
John

Mark D. Zacharias wrote:
"JohnC" wrote in message
...
"jakdedert" wrote in message
.. .
Mark D. Zacharias wrote:
(Just where are those outputs, anyway?)
jak
The outputs are those little black bridge rectifier-looking things
attached to the rear panel. I once subbed a set of 2SD313's for them,
but the basing is the reverse of a TO-220 package, if memory serves.
This model was one of my earliest "wiz-bang" repairs where I had to
improvise to get the thing running. Even in 1985 or thereabouts there
was no support from Harman on this model.

Which goes back to the question, is there some compelling reason to want
to fix this thing? It's probably not even worth the effort unless you
just need it to fill out your HK collection - they were pretty rare.


Mark Z.
The OP stated that he's had it since new, so I'd guess a fairly strong
sentimental attachment.

jak
Thank you all for your assistance and suggestions to help me with this hum
problem. I opened it up again today and removed the front too to better
inspect connections on the front panel. With the unit on, I tapped all
over the unit with a non-conductive tool. I was unable to have any effect
on the hum. I loosened and tightened many screws. Especially those that
appear to provide some grounding. No change. I found no connections that
appeared suspect.

I suppose the next step is to test the caps with an ESR meter. This is
probably beyond my ability and will involve the purchase of such a unit.
So I think I will button the unit up, and for now keep it on 'Monitor' and
use an external tuner on the monitor inputs. There is no hum when using
Monitor.

Yes this unit is a relic and in fact purchased by my wife new in the early
70's. Perhaps not worth the service fee for repair, but it provides a
connection to the past so I'll keep in for her a bit longer.

Thanks again.

John



Was the hum only on the (FM) radio section? That would have narrowed it down
somewhat...

Mark Z.


Mark,

As I recall from a question that John replied to earlier, his hum
problem was on all sources EXCEPT the tape monitor switch. I suspect a
pre-amp power supply issue, or a ground fault of some sort. It would be
nice to have a print of the thing, but I don't.

Regards,
Tim Schwartz
Bristol Electronics

On Mar 2, 7:07*pm, "JohnC" wrote:
Thank you all for your assistance and suggestions to help me with this
hum problem. *I opened it up again today and removed the front too to
better inspect connections on the front panel. *With the unit on, I
tapped all over the unit with a non-conductive tool. *I was unable to
have any effect on the hum. *I loosened and tightened many screws.
Especially those that appear to provide some grounding. No change. *I
found no connections that appeared suspect.

I suppose the next step is to test the caps with an ESR meter. *This is
probably beyond my ability and will involve the purchase of such a unit..
So I think I will button the unit up, and for now keep it on 'Monitor'
and use an external tuner on the monitor inputs. *There is no hum when
using Monitor.

Yes this unit is a relic and in fact purchased by my wife new in the
early 70's. *Perhaps not worth the service fee for repair, but it
provides a connection to the past so I'll keep in for her a bit longer.

Thanks again.

John

Was the hum only on the (FM) radio section? That would have narrowed it
down somewhat...

Mark Z.

Mark,
The hum is there for phono, AM, and FM - so all source inputs.
John

Didn't you report earlier that you tried connecting a separate audio
source into the tape monitor inputs and the hum went away? Did you
mean completely, i.e. no hum problem at all in this case? That really
sounds like a (mechanical) grounding problem to me. Especially since
the volume and tone controls worked for this test, which would
indicate that it isn't a problem with preamp/tone power supply
ripple. Good luck.

"Tim Schwartz" wrote in message
news:MnSyj.5598$dB.2154@trnddc01...
Mark D. Zacharias wrote:
"JohnC" wrote in message
...
"jakdedert" wrote in message
.. .
Mark D. Zacharias wrote:
(Just where are those outputs, anyway?)
jak
The outputs are those little black bridge rectifier-looking things
attached to the rear panel. I once subbed a set of 2SD313's for them,
but the basing is the reverse of a TO-220 package, if memory serves.
This model was one of my earliest "wiz-bang" repairs where I had to
improvise to get the thing running. Even in 1985 or thereabouts there
was no support from Harman on this model.

Which goes back to the question, is there some compelling reason to
want to fix this thing? It's probably not even worth the effort unless
you just need it to fill out your HK collection - they were pretty
rare.


Mark Z.
The OP stated that he's had it since new, so I'd guess a fairly strong
sentimental attachment.

jak
Thank you all for your assistance and suggestions to help me with this
hum problem. I opened it up again today and removed the front too to
better inspect connections on the front panel. With the unit on, I
tapped all over the unit with a non-conductive tool. I was unable to
have any effect on the hum. I loosened and tightened many screws.
Especially those that appear to provide some grounding. No change. I
found no connections that appeared suspect.

I suppose the next step is to test the caps with an ESR meter. This is
probably beyond my ability and will involve the purchase of such a unit.
So I think I will button the unit up, and for now keep it on 'Monitor'
and use an external tuner on the monitor inputs. There is no hum when
using Monitor.

Yes this unit is a relic and in fact purchased by my wife new in the
early 70's. Perhaps not worth the service fee for repair, but it
provides a connection to the past so I'll keep in for her a bit longer.

Thanks again.

John



Was the hum only on the (FM) radio section? That would have narrowed it
down somewhat...

Mark Z.
Mark,

As I recall from a question that John replied to earlier, his hum problem
was on all sources EXCEPT the tape monitor switch. I suspect a pre-amp
power supply issue, or a ground fault of some sort. It would be nice to
have a print of the thing, but I don't.

Regards,
Tim Schwartz
Bristol Electronics

That is correct. Hum is present on all sources EXCEPT the tape monitor
switch. I can pug in an external tuner on the tape monitor input and there
is no hum when switched to MONITOR.

John

On Mar 6, 9:00*pm, "JohnC" wrote:
"Tim Schwartz" wrote in message

news:MnSyj.5598$dB.2154@trnddc01...



Mark D. Zacharias wrote:
"JohnC" wrote in message
. ..
"jakdedert" wrote in message
t...
Mark D. Zacharias wrote:
(Just where are those outputs, anyway?)
jak
The outputs are those little black bridge rectifier-looking things
attached to the rear panel. I once subbed a set of 2SD313's for them,
but the basing is the reverse of a TO-220 package, if memory serves.
This model was one of my earliest "wiz-bang" repairs where I had to
improvise to get the thing running. Even in 1985 or thereabouts there
was no support from Harman on this model.

Which goes back to the question, is there some compelling reason to
want to fix this thing? It's probably not even worth the effort unless
you just need it to fill out your HK collection - they were pretty
rare.

Mark Z.
The OP stated that he's had it since new, so I'd guess a fairly strong
sentimental attachment.

jak
Thank you all for your assistance and suggestions to help me with this
hum problem. *I opened it up again today and removed the front too to
better inspect connections on the front panel. *With the unit on, I
tapped all over the unit with a non-conductive tool. *I was unable to
have any effect on the hum. *I loosened and tightened many screws.
Especially those that appear to provide some grounding. No change. *I
found no connections that appeared suspect.

I suppose the next step is to test the caps with an ESR meter. *This is
probably beyond my ability and will involve the purchase of such a unit.