Repair info for Harman Kardon HK620 amplifier

I

Ian Cameron

Guest
Hi,

I have been given a Harman Kardon amplifier to repair, model HK620.

The symptom is that there is no audio output on either channel from any
of the inputs. The amplifier didn't go faulty in operation. The owner
got it out, tried it and found that it no longer works.

Naturally, I first suspected a power supply problem as being the cause
which would affect both channels.

After checking all the usual things such as fuses, the main power rails
which are +/- 50V, I started to trace the audio signal around the board.

I have managed to trace the audio on each channel to transistors Q402
and Q404 with a scope. From there I cannot find a signal.

Are there any common faults other than the main power transistors
failing (though both failing together surely seems odd?) which would
cause the failure of both channels together? Perhaps a cut out
mechanism which has gone faulty?

Any information would be appreciated, circuit schematics, general things
to look at etc.

Thanks.

--
Cheers, Ian.
 
On Tue, 02 Mar 2004 16:01:03 +0000 Ian Cameron
<i.a.cameron@open.ac.uk> wrote:

Are there any common faults other than the main power transistors
failing (though both failing together surely seems odd?) which would
cause the failure of both channels together? Perhaps a cut out
mechanism which has gone faulty?
Click to expand...
I would suspect the loss of some voltage supply used by both channels.
There are often several different voltages used in amplifiers.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------
 
Can you / will you accept a PDF service manual as an attachment? It's about
1.73 meg.

Mark Z.

--
Please reply only to Group. I regret this is necessary. Viruses and spam
have rendered my regular e-mail address useless.


"Ian Cameron" <i.a.cameron@open.ac.uk> wrote in message
news:%f21c.16238$Y%6.1477463@wards.force9.net...
Hi,

I have been given a Harman Kardon amplifier to repair, model HK620.

The symptom is that there is no audio output on either channel from any
of the inputs. The amplifier didn't go faulty in operation. The owner
got it out, tried it and found that it no longer works.

Naturally, I first suspected a power supply problem as being the cause
which would affect both channels.

After checking all the usual things such as fuses, the main power rails
which are +/- 50V, I started to trace the audio signal around the board.

I have managed to trace the audio on each channel to transistors Q402
and Q404 with a scope. From there I cannot find a signal.

Are there any common faults other than the main power transistors
failing (though both failing together surely seems odd?) which would
cause the failure of both channels together? Perhaps a cut out
mechanism which has gone faulty?

Any information would be appreciated, circuit schematics, general things
to look at etc.

Thanks.

--
Cheers, Ian.
Click to expand...
 
Hi Mark,

Yes please! By email attachment would be fine.

Thanks VERY much indeed.

--
Cheers, Ian.


Mark D. Zacharias wrote:
Can you / will you accept a PDF service manual as an attachment? It's about
1.73 meg.

Mark Z.

--
Please reply only to Group. I regret this is necessary. Viruses and spam
have rendered my regular e-mail address useless.


"Ian Cameron" <i.a.cameron@open.ac.uk> wrote in message
news:%f21c.16238$Y%6.1477463@wards.force9.net...

Hi,

I have been given a Harman Kardon amplifier to repair, model HK620.

The symptom is that there is no audio output on either channel from any
of the inputs. The amplifier didn't go faulty in operation. The owner
got it out, tried it and found that it no longer works.

Naturally, I first suspected a power supply problem as being the cause
which would affect both channels.

After checking all the usual things such as fuses, the main power rails
which are +/- 50V, I started to trace the audio signal around the board.

I have managed to trace the audio on each channel to transistors Q402
and Q404 with a scope. From there I cannot find a signal.

Are there any common faults other than the main power transistors
failing (though both failing together surely seems odd?) which would
cause the failure of both channels together? Perhaps a cut out
mechanism which has gone faulty?

Any information would be appreciated, circuit schematics, general things
to look at etc.

Thanks.

--
Cheers, Ian.
Click to expand...
 
Jim Adney wrote:
I would suspect the loss of some voltage supply used by both channels.
There are often several different voltages used in amplifiers.
Click to expand...
I will have another look. Hopefully a service manual will be on its way
here soon, which will be a massive help!

Thanks.

--
Cheers, Ian.
 
Received and printed thanks!

Hopefully I'll get a chance to take a look at this amp again soon, and
then perhaps I can post information on the cause of the problem back to
the news group.

--
Cheers, Ian.

Ian Cameron wrote:
Hi Mark,

Yes please! By email attachment would be fine.

Thanks VERY much indeed.

--
Cheers, Ian.


Mark D. Zacharias wrote:

Can you / will you accept a PDF service manual as an attachment? It's
about
1.73 meg.

Mark Z.

--
Please reply only to Group. I regret this is necessary. Viruses and spam
have rendered my regular e-mail address useless.


"Ian Cameron" <i.a.cameron@open.ac.uk> wrote in message
news:%f21c.16238$Y%6.1477463@wards.force9.net...

Hi,

I have been given a Harman Kardon amplifier to repair, model HK620.

The symptom is that there is no audio output on either channel from any
of the inputs. The amplifier didn't go faulty in operation. The owner
got it out, tried it and found that it no longer works.

Naturally, I first suspected a power supply problem as being the cause
which would affect both channels.

After checking all the usual things such as fuses, the main power rails
which are +/- 50V, I started to trace the audio signal around the board.

I have managed to trace the audio on each channel to transistors Q402
and Q404 with a scope. From there I cannot find a signal.

Are there any common faults other than the main power transistors
failing (though both failing together surely seems odd?) which would
cause the failure of both channels together? Perhaps a cut out
mechanism which has gone faulty?

Any information would be appreciated, circuit schematics, general things
to look at etc.

Thanks.

--
Cheers, Ian.
Click to expand...
 
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