My Harmon Kardon receiver recently started to hum. It does it regardless of
which input is selected. The hum varies with the volume control. I opened
the unit and tapped on various components with a wood stick. This had no
affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but lack
electronics skills. No scope either. What could be the cause of the hum? Is
this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John

JohnC wrote:
My Harmon Kardon receiver recently started to hum. It does it regardless of
which input is selected. The hum varies with the volume control. I opened
the unit and tapped on various components with a wood stick. This had no
affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but lack
electronics skills. No scope either. What could be the cause of the hum? Is
this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


Those big grey capacitors near the power transformer are likely candidates.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"JohnC" wrote in message
.. .
My Harmon Kardon receiver recently started to hum. It does it regardless
of which input is selected. The hum varies with the volume control. I
opened the unit and tapped on various components with a wood stick. This
had no affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but
lack electronics skills. No scope either. What could be the cause of the
hum? Is this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


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

"Arfa Daily" wrote in message
...

"JohnC" wrote in message
.. .
My Harmon Kardon receiver recently started to hum. It does it regardless
of which input is selected. The hum varies with the volume control. I
opened the unit and tapped on various components with a wood stick. This
had no affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but
lack electronics skills. No scope either. What could be the cause of the
hum? Is this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


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.

On Mon, 4 Feb 2008 21:23:17 -0600, "JohnC"
wrote:

My Harmon Kardon receiver recently started to hum. It does it regardless of
which input is selected. The hum varies with the volume control. I opened
the unit and tapped on various components with a wood stick. This had no
affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but lack
electronics skills. No scope either. What could be the cause of the hum? Is
this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John

Varying with the volume says the source of hum is before the volume
control. If you have inputs connected you can quickly eliminate a
ground or ground loop problem by unplugging the inputs, and shorting
the signal to ground connections right at the RCA plugs.

If that gets rid of it you look for a grounding problem between the
amp and signal source.

If that isn't the situation, the gray caps are the likely culprits and
I'd just replace them. They don't cost an arm and leg and it is an
old set and caps will lose some electrolyte over time reducing
capacity and increasing hum.

Inspect the seals on the caps - the end where the plus lead goes into
the caps - and hint of corrosion or a bulge (pimple) in the end seal
is a sign that cap is bad - but they can fail with no visual clues
too.

The large vertical cap is the main filter cap and you should look at
the bottom to see if there's leakage. Generally, the main filter
cap(s) going out will cause hum at all volume settings - but not
always.

The 2,200 uf / 35 volt caps are power supply filters also, from the
looks of it. The 470 by the 2,200's looks like it may be part of a
filter for a regulator so that one is suspect. The two other 470's I
can't tell without a schematic - they are either filters for the pre
amp board or speaker coupling caps. I'd guess coupling caps.

With great care and a little tape so you don't become part of a
circuit, you can just hand hold a cap and bridge the ones in there
with a new one (470/35 or so) the hum will be eliminated or decreased
when they are bridged. Discharge against some metal between checks.
A smaller capacity cap (same or higher voltage) than the one you are
testing is desirable - since it will drag down the supply momentarily
when it first makes contact and that may not be good for the output
stages.

or you can connect it backwards and cause smoke and fire or have it
blow up in your fingers - repair people do it all the time, but you
have to be comfortable with the idea. Dry hands, loose grip, and no
cuts and a 35 volt supply shouldn't shock.

Or just replace those three gray caps on the left and hope for the
best.


--

One point hasn't been brought up.

If one or more of the caps are bad, then it's likely you'll hear hum even
with the volume control all the way down. If there is no hum with the
control the way down, the problem is probably elsewhere.

Regardless, it wouldn't be a bad idea to simply replace all the PS
electrolytics in a 35-year old receiver.

"William Sommerwerck" wrote in message
...
One point hasn't been brought up.

If one or more of the caps are bad, then it's likely you'll hear hum even
with the volume control all the way down. If there is no hum with the
control the way down, the problem is probably elsewhere.

Regardless, it wouldn't be a bad idea to simply replace all the PS
electrolytics in a 35-year old receiver.



I'm not a great advocate of the 'shotgun' approach with this type of
equipment. A lot of times, a person who has little electronics skill, as
this poster told us he didn't, can cause himself more trouble by just
replacing items 'willy-nilly'. It's very easy to make a wiring or polarity
mistake. And once he has, he will be in even worse trouble than before, as
he now has both the original problem, and the one he's caused himself ...

I did actually say in my first post in this thread, that hum as a result of
a power supply problem - for example a bad cap - will not usually be
affected by the volume control, so by implication, will still be there with
the volume at minimum.

Arfa

"Arfa Daily" wrote in message
...

I did actually say in my first post in this thread, that hum as a result
of a power supply problem -- for example a bad cap -- will not usually
be affected by the volume control, so by implication, will still be there
with the volume at minimum.

Yes, you did say that. But one might reasonably assume that the PS hum ahead
of the volume control would add to the hum following the volume control.

On 2/5/08 1:23 AM, in article , "Arfa
Daily" wrote:


"JohnC" wrote in message
.. .
My Harmon Kardon receiver recently started to hum. It does it regardless
of which input is selected. The hum varies with the volume control. I
opened the unit and tapped on various components with a wood stick. This
had no affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but
lack electronics skills. No scope either. What could be the cause of the
hum? Is this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


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.

Not necessarily, and certainly not a front end hum entry problem. If it is
a general power supply filtering problem (most likely) the hum sound can
readily be altered by varying the volume control due to hum getting into the
preamp.

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.

See above.


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

On 2/5/08 8:45 AM, in article , "Arfa
Daily" wrote:


"William Sommerwerck" wrote in message
...
One point hasn't been brought up.

If one or more of the caps are bad, then it's likely you'll hear hum even
with the volume control all the way down. If there is no hum with the
control the way down, the problem is probably elsewhere.

Regardless, it wouldn't be a bad idea to simply replace all the PS
electrolytics in a 35-year old receiver.



I'm not a great advocate of the 'shotgun' approach with this type of
equipment. A lot of times, a person who has little electronics skill, as
this poster told us he didn't, can cause himself more trouble by just
replacing items 'willy-nilly'. It's very easy to make a wiring or polarity
mistake. And once he has, he will be in even worse trouble than before, as
he now has both the original problem, and the one he's caused himself ...

I did actually say in my first post in this thread, that hum as a result of
a power supply problem - for example a bad cap - will not usually be
affected by the volume control, so by implication, will still be there with
the volume at minimum.

Arfa




But the loudness of the hum will, like a mixer, follow the volume control if
the problem is a power filter common to the preamp.

In article ,
says...
One point hasn't been brought up.

If one or more of the caps are bad, then it's likely you'll hear hum even
with the volume control all the way down. If there is no hum with the
control the way down, the problem is probably elsewhere.

Regardless, it wouldn't be a bad idea to simply replace all the PS
electrolytics in a 35-year old receiver.




Reading all this I'd say a basic overhaul is in order. Replace the
electrolytic caps, the voltage regulator and the volume control pot and
it'll probably last another 35 years. Of course by then some vulture
will snap up the FM bands.

"Don Bowey" wrote in message
...
On 2/5/08 1:23 AM, in article ,
"Arfa
Daily" wrote:


"JohnC" wrote in message
.. .
My Harmon Kardon receiver recently started to hum. It does it
regardless
of which input is selected. The hum varies with the volume control. I
opened the unit and tapped on various components with a wood stick. This
had no affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but
lack electronics skills. No scope either. What could be the cause of the
hum? Is this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


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.

Not necessarily, and certainly not a front end hum entry problem. If it
is
a general power supply filtering problem (most likely) the hum sound can
readily be altered by varying the volume control due to hum getting into
the
preamp.

Well, a matter of semantics here. This problem is obviously not an input
cabling problem, as it is not confined to one input. I was merely using that
as an illustration of what hum that is varied by the volume control is most
usually as a result of, and why in this case, it was slightly odd that it
was on all inputs and channels.

When I say "front end", I am referring to anything 'North' of the volume
control, which in an amp of this age, is a mechanical control located
between the 'front end' which includes all the preamp, input selection and
tone control sections, and the power amps. Thus, if it is altered by the
volume control, then the hum is getting in 'front end' as opposed to being
on the main supply rails which feed the output stages. Depending on whether
the preamp rails are produced from their own secondary winding on the
transformer, with their own rectifier and filter caps, or are regulated down
from the main output stage rails, will determine how "most likely" the
problem is one of caps. The '330, for instance, uses only a single winding,
rectifier, and main smoothing, from which other rails are then derived. I
don't know what the situation is on the '230. Certainly, on the photo, I can
only see one winding coming round to where all the above-chassis caps are,
but that's not to say that there are not other windings going off to
circuitry under the chassis, where we can't see. If it is a multi-winding
transformer, then I agree that there is a distinct possibility that there
may be hum just on the supply rails to the preamps.


Arfa

Arfa Daily wrote:

"William Sommerwerck" wrote in message
...

One point hasn't been brought up.

If one or more of the caps are bad, then it's likely you'll hear hum even
with the volume control all the way down. If there is no hum with the
control the way down, the problem is probably elsewhere.

Regardless, it wouldn't be a bad idea to simply replace all the PS
electrolytics in a 35-year old receiver.




I'm not a great advocate of the 'shotgun' approach with this type of
equipment. A lot of times, a person who has little electronics skill, as
this poster told us he didn't, can cause himself more trouble by just
replacing items 'willy-nilly'. It's very easy to make a wiring or polarity
mistake. And once he has, he will be in even worse trouble than before, as
he now has both the original problem, and the one he's caused himself ...

I did actually say in my first post in this thread, that hum as a result of
a power supply problem - for example a bad cap - will not usually be
affected by the volume control, so by implication, will still be there with
the volume at minimum.

Arfa



AFAICT, he never said there was no hum with the volume down -- just that
it varied with the volume control.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"William Sommerwerck" wrote in message
news
"Arfa Daily" wrote in message
...

I did actually say in my first post in this thread, that hum as a result
of a power supply problem -- for example a bad cap -- will not usually
be affected by the volume control, so by implication, will still be there
with the volume at minimum.

Yes, you did say that. But one might reasonably assume that the PS hum
ahead
of the volume control would add to the hum following the volume control.



As Don has said, it only works as a power supply problem, if the preamps
have their own supply rails, derived from their own transformer winding,
rectifier, and filter cap(s), in which case, a failed cap, or a leaky diode,
will place ripple on the preamp supplies, giving an audible hum which will
completely disappear, when the volume is turned to minimum. If the preamp
rails are derived from the main power amp rails, as is quite often the case,
then any cap or diode failure that produced ripple on the main rails, would
cause the audible hum to be present even with the volume at minimum.
Downstream decoupling on the preamp rails, would likely remove most, if not
all of the ripple from those rails, so when the volume was turned up, there
would be no additional amplified hum contribution from the preamps.

Arfa

"CJT" wrote in message
...
Arfa Daily wrote:

"William Sommerwerck" wrote in message
...

One point hasn't been brought up.

If one or more of the caps are bad, then it's likely you'll hear hum even
with the volume control all the way down. If there is no hum with the
control the way down, the problem is probably elsewhere.

Regardless, it wouldn't be a bad idea to simply replace all the PS
electrolytics in a 35-year old receiver.




I'm not a great advocate of the 'shotgun' approach with this type of
equipment. A lot of times, a person who has little electronics skill, as
this poster told us he didn't, can cause himself more trouble by just
replacing items 'willy-nilly'. It's very easy to make a wiring or
polarity mistake. And once he has, he will be in even worse trouble than
before, as he now has both the original problem, and the one he's caused
himself ...

I did actually say in my first post in this thread, that hum as a result
of a power supply problem - for example a bad cap - will not usually be
affected by the volume control, so by implication, will still be there
with the volume at minimum.

Arfa



AFAICT, he never said there was no hum with the volume down -- just that
it varied with the volume control.

Ah ! Quite right, he did. Very likely the hum does go away completely with
the vol turned right down, but having read it again with the possibility
that it doesn't in mind, that makes a difference to my thinking, and makes
what William said more of a possibility. Regardless, either way, this should
not be a difficult problem to locate, but might be a shade too 'electronic'
for the OP to diagnose on his own, with the limited skills that he tells us
that he has in the field.

Arfa

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"Arfa Daily" wrote in message
...

Well, a matter of semantics here. This problem is obviously
not an input cabling problem, as it is not confined to one input.

Well, you could have a ground loop problem with the cable TV system, but
that's not the sort of thing that would _suddenly_ show up.

By the way, if you have such a problem, you can get rid of it by connecting
two true baluns back-to-back and inserting them in the cable line. There are
speciality isolation transformers for this problem, but they're pricey, and
all you gain is a bit less insertion loss.


When I say "front end", I am referring to anything "North" of the volume
control, which in an amp of this age, is a mechanical control located
between the 'front end' which includes all the preamp, input selection
and tone control sections, and the power amps.

Is that true? I haven't looked at any schematics recently, but my memory is
that volume controls are not always at the "end" of the input chain.

On 2/5/08 6:15 PM, in article , "Arfa
Daily" wrote:

(snip)

If it is a multi-winding transformer, then I agree that there is a distinct
possibility that there may be hum just on the supply rails to the preamps.


Arfa



That wasn't my point.

My point was that even if there is a faulty DC supply common to both the
amplifier and the preamp (typical low-end), changes in the volume control
setting will still be heard as an amplitude or character sound change in the
hum from the speaker.

Don Bowey wrote:
On 2/5/08 6:15 PM, in article , "Arfa
Daily" wrote:

(snip)

If it is a multi-winding transformer, then I agree that there is a distinct
possibility that there may be hum just on the supply rails to the preamps.

Arfa



That wasn't my point.

My point was that even if there is a faulty DC supply common to both the
amplifier and the preamp (typical low-end), changes in the volume control
setting will still be heard as an amplitude or character sound change in the
hum from the speaker.


My issue is that--all too often--someone drops a problem in here, for
which there is a pretty standard, simple decision-tree diagnosis
process. Then we're left to dangle for days, speculating on possible
solutions, while the OP is totally silent.

Until he comes back, all is speculation.

jak

"William Sommerwerck" wrote in message
...
"Arfa Daily" wrote in message
...

Well, a matter of semantics here. This problem is obviously
not an input cabling problem, as it is not confined to one input.

Well, you could have a ground loop problem with the cable TV system, but
that's not the sort of thing that would _suddenly_ show up.

By the way, if you have such a problem, you can get rid of it by
connecting
two true baluns back-to-back and inserting them in the cable line. There
are
speciality isolation transformers for this problem, but they're pricey,
and
all you gain is a bit less insertion loss.


When I say "front end", I am referring to anything "North" of the volume
control, which in an amp of this age, is a mechanical control located
between the 'front end' which includes all the preamp, input selection
and tone control sections, and the power amps.

Is that true? I haven't looked at any schematics recently, but my memory
is
that volume controls are not always at the "end" of the input chain.


Pretty much all the ones I've seen, that's the 'standard' arrangement.

Arfa

"Don Bowey" wrote in message
...
On 2/5/08 6:15 PM, in article ,
"Arfa
Daily" wrote:

(snip)

If it is a multi-winding transformer, then I agree that there is a
distinct
possibility that there may be hum just on the supply rails to the
preamps.


Arfa



That wasn't my point.

My point was that even if there is a faulty DC supply common to both the
amplifier and the preamp (typical low-end), changes in the volume control
setting will still be heard as an amplitude or character sound change in
the
hum from the speaker.

Maybe. But by no means guaranteed. Low(er) rails derived from the main
output rails, will usually have their own decoupling caps, and if they are
derived via monolithic regs of the 78 / 79xx series, then the typical ripple
rejection of some 80dB that these devices have, will pretty much knock any
ripple on the head, before you even start counting in downstream decoupling
caps. Thus, my point, that you could have a DC fault giving rise to dirty
'raw' rails fed directly to the power amps, whilst still maintaining clean
low rails to the preamps, in which case, the volume control will have little
or no effect on the hum.

Anyway, this is just becoming a worthless discussion of perhaps's, maybe's
and diagnostic experience, as Jak suggests below. I can only contribute
suggestions based on what 30 odd years of repairing this stuff on a daily
basis, has taught me about faults like this.

Arfa

My Harmon Kardon receiver recently started to hum. It does it
regardless
of which input is selected. The hum varies with the volume control. I
opened the unit and tapped on various components with a wood stick. This
had no affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but
lack electronics skills. No scope either. What could be the cause of the
hum? Is this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


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

"JohnC" wrote in message
.. .

My Harmon Kardon receiver recently started to hum. It does it
regardless
of which input is selected. The hum varies with the volume control. I
opened the unit and tapped on various components with a wood stick.
This had no affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but
lack electronics skills. No scope either. What could be the cause of
the hum? Is this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


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.

The volume control was recently mentioned as a possible trouble site...

When I was collecting KLH Model Eight radios, I had one that suffered from
hum and volume control scratchiness. Much to my surprise, simply flushing
the control cleared up the hum.

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.

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

This suggests that there's nothing wrong with the power supply, as the tape
monitor is part of the overall input-selection circuitry.

"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.

***Major SNIP***

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.



John,

Have you tried feeding a source into the monitor input and see if the
unit sounds OK? I'm guessing it will. While I don't know the HK-230A,
I have seen receivers that the tape monitor switch feeds the volume
control directly (or nearly so) eliminating the the tone control amps.

I strongly suspect that you have a low level (regulated) power supply
failure that is causing the hum. Looking at the power supplies that
feed the preamp circuits with an oscilloscope is going to be the hot
ticket here.

Tim Schwartz
Bristol Electronics

John,

Have you tried feeding a source into the monitor input and see if the unit
sounds OK? I'm guessing it will. While I don't know the HK-230A, I have
seen receivers that the tape monitor switch feeds the volume control
directly (or nearly so) eliminating the the tone control amps.

I strongly suspect that you have a low level (regulated) power supply
failure that is causing the hum. Looking at the power supplies that feed
the preamp circuits with an oscilloscope is going to be the hot ticket
here.

Tim Schwartz
Bristol Electronics

Wouldn't checking ESR on the power supply caps be the first thing for a unit
of that age? I have found that to generally be the issue on the old stuff I
have worked on.

WT

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.

John,

Have you tried feeding a source into the monitor input and see if the unit
sounds OK? I'm guessing it will. While I don't know the HK-230A, I have
seen receivers that the tape monitor switch feeds the volume control
directly (or nearly so) eliminating the the tone control amps.

I strongly suspect that you have a low level (regulated) power supply
failure that is causing the hum. Looking at the power supplies that feed
the preamp circuits with an oscilloscope is going to be the hot ticket
here.

Tim Schwartz
Bristol Electronics

Tim,
Yes, when I plugged a source into the monitor input there is no hum. All
controls, bass, treble, balance, volume work for the monitor source.
Another item of interest- one of the channels begins to cut out after about
half a minute while using the monitor input. I can unplug the RCA jacks and
reinsert and both channels come back, only to have one of the channels drop
out again after about half a minute.

John

On Sat, 16 Feb 2008 11:15:57 -0600, "JohnC"
wrote:


My Harmon Kardon receiver recently started to hum. It does it
regardless
of which input is selected. The hum varies with the volume control. I
opened the unit and tapped on various components with a wood stick. This
had no affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but
lack electronics skills. No scope either. What could be the cause of the
hum? Is this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:


I'd try jumping the 3 470uf and the 1000uf capacitors with new good
caps. If this doesn't work, I'd sub the electrolytic caps on that
stand up board. If you have an esr meter, it would speed up the
process. Chuck
http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


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

JohnC wrote:
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.
John,

Have you tried feeding a source into the monitor input and see if the unit
sounds OK? I'm guessing it will. While I don't know the HK-230A, I have
seen receivers that the tape monitor switch feeds the volume control
directly (or nearly so) eliminating the the tone control amps.

I strongly suspect that you have a low level (regulated) power supply
failure that is causing the hum. Looking at the power supplies that feed
the preamp circuits with an oscilloscope is going to be the hot ticket
here.

Tim Schwartz
Bristol Electronics

Tim,
Yes, when I plugged a source into the monitor input there is no hum. All
controls, bass, treble, balance, volume work for the monitor source.
Another item of interest- one of the channels begins to cut out after about
half a minute while using the monitor input. I can unplug the RCA jacks and
reinsert and both channels come back, only to have one of the channels drop
out again after about half a minute.

John


This is starting to sound like the possibility of either bad solder
joints, corroded internal connectors....

Also, it's been reported here that some older stuff develops loose
circuit board to chassis connections which can be solved by merely
backing off and reseating any screws which hold them down.

Clean EVERYTHING--controls, switches, jacks etc. Pull and reseat all
connectors. Then, with the amp

Sorry, hit send too quickly....

JohnC wrote:
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.
John,

Have you tried feeding a source into the monitor input and see if the unit
sounds OK? I'm guessing it will. While I don't know the HK-230A, I have
seen receivers that the tape monitor switch feeds the volume control
directly (or nearly so) eliminating the the tone control amps.

I strongly suspect that you have a low level (regulated) power supply
failure that is causing the hum. Looking at the power supplies that feed
the preamp circuits with an oscilloscope is going to be the hot ticket
here.

Tim Schwartz
Bristol Electronics

Tim,
Yes, when I plugged a source into the monitor input there is no hum. All
controls, bass, treble, balance, volume work for the monitor source.
Another item of interest- one of the channels begins to cut out after about
half a minute while using the monitor input. I can unplug the RCA jacks and
reinsert and both channels come back, only to have one of the channels drop
out again after about half a minute.

John


This is starting to sound like the possibility of either bad solder
joints, corroded internal connectors....

Also, it's been reported here that some older stuff develops loose
circuit board to chassis connections which can be solved by merely
backing off and reseating any screws which hold them down.

Clean EVERYTHING--controls, switches, jacks etc. Pull and reseat all
connectors. If the problem still exists, poke around the inside with an
insulated probe and see if you can cause any change in the amplitude of
the hum...or in the case of the tape input, can get the bad channel to
either cut out or in.

Check back....

jak

On Feb 4, 11:23*pm, "JohnC" wrote:
My Harmon Kardon receiver recently started to hum. *It does it regardless of
which input is selected. *The hum varies with the volume control. I opened
the unit and tapped on various components with a wood stick. This had no
affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? *I'm good with tools but lack
electronics skills. No scope either. What could be the cause of the hum? *Is
this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

*http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John

what you should do is if you have a tester meter check the voltage
regulater and capasitors

wrote in message
...
On Feb 4, 11:23 pm, "JohnC" wrote:
My Harmon Kardon receiver recently started to hum. It does it regardless
of
which input is selected. The hum varies with the volume control. I opened
the unit and tapped on various components with a wood stick. This had no
affect on the hum.

This is an old unit that I have owned new since early 70s. Perhaps this
might not be worth getting serviced by a shop? I'm good with tools but
lack
electronics skills. No scope either. What could be the cause of the hum?
Is
this something that is fairly easy to replace/repair?

Here is a pic of the circuit board:

http://home.everestkc.net/upperquad/...rmonKardon.jpg

Thanks
John


Gads. I worked on one of these once. Had these really unusual Sanyo output
transistors.

Does it have some sentimental value or something?

Mark Z.

jakdedert wrote:
Sorry, hit send too quickly....

JohnC wrote:
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.
John,

Have you tried feeding a source into the monitor input and see if the
unit sounds OK? I'm guessing it will. While I don't know the
HK-230A, I have seen receivers that the tape monitor switch feeds the
volume control directly (or nearly so) eliminating the the tone
control amps.

I strongly suspect that you have a low level (regulated) power supply
failure that is causing the hum. Looking at the power supplies that
feed the preamp circuits with an oscilloscope is going to be the hot
ticket here.

Tim Schwartz
Bristol Electronics

Tim,
Yes, when I plugged a source into the monitor input there is no hum.
All controls, bass, treble, balance, volume work for the monitor
source. Another item of interest- one of the channels begins to cut
out after about half a minute while using the monitor input. I can
unplug the RCA jacks and reinsert and both channels come back, only to
have one of the channels drop out again after about half a minute.

John

This is starting to sound like the possibility of either bad solder
joints, corroded internal connectors....

Also, it's been reported here that some older stuff develops loose
circuit board to chassis connections which can be solved by merely
backing off and reseating any screws which hold them down.

Clean EVERYTHING--controls, switches, jacks etc. Pull and reseat all
connectors. If the problem still exists, poke around the inside with an
insulated probe and see if you can cause any change in the amplitude of
the hum...or in the case of the tape input, can get the bad channel to
either cut out or in.

Check back....

jak

Sorry (again)...should have read the OP more carefully and looked at the
picture. My advice about probing was not very timely, having already
been attempted by the OP.

That said, to be clear, it should have been done with the unit powered
up. It's not obvious whether that was the case, although I'd assume so.
I didn't make that clear in my post, either.

Having looked at the pic (finally), it's striking just how old this
relic is. It obviously wasn't all that well-built to begin with, IMO.
I'm surprised by the diminutive size of the power transformer and lack
of heat sinking (Just where are those outputs, anyway?)...not to mention
the amount of point-to-point wiring employed.

Nonetheless, my advice is reinforced by the view. There's a lot of
potential for problems caused by strictly mechanical aging. While I
wouldn't expect this unit to develop a lot of heat; heat-related
electrical issues could still develop. Those would manifest as dried
out capacitors, or fatigued solder joints...possibly defective transistors.

I think if this one crossed my bench, I'd look at it as much a
'restoration' as a repair. It's from an time where both mechanical and
electrical design were still in flux from the tube era. Looking at it I
would guess it to be older than stated. It looks more like something
from the mid-60's, as opposed to early 70's.

jak

(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.

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.

I don't know how well-made this model is -- at least one poster has
suggested it's not of the highest quality. But I know how _I_ feel... If
something is well-made, I expect it to last "forever". And I don't like it
when I breaks down.

I have a LUX Laboratory Reference System, and it all works, despite being
over 30 years old. It's my bedroom system, and I doubt I'd ever sell it. If
anything broke, I'd try to fix it.

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

"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

"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.