"David Farber" wrote in message
...
This Harman Kardon AVR210 receiver has no audio output in any mode.
Customer
said it just went out all of a sudden. I was able to find a copy of the
service manual he
http://eserviceinfo.com/downloadsm/4...on_AVR210.html It's in
four parts and you'll need a utility that can unpack a rar file to see it.
The manual is 135 pages so when referring to it, I've included the page
numbers.

I performed the part modification as suggested on page 19. It didn't
correct
the problem.

Then I traced signal as shown in the chart on pages 25-26. Using the
direct
input, I was able to get audio out of the tape output jacks. There is no
output from the preamp output jacks. There is no protection relay that I
can
see and there is no dc offset at the power amplifier output.

Referring to the signal flow chart on page 26, the audio input signal is
present on pins 4 and 25 of IC 706 (electronic volume control) but missing
on pins 3 and 26 of IC 706. The schematic of this circuit is on page 116.
However when I rotate the volume control, the audio will appear as long as
the knob is moving. As soon as the control is left alone, the audio mutes.
The output pins are 3 and 26, of IC 706. The signal appears to be clean
though I estimate the speaker output to be about 30dB less than where it's
supposed to be while it is present. If I bridge the input to the output
pins
of IC706, an attenuated signal appears but it's too low for any output to
register at the speakers.

Now, referring to the block diagram on page 30, you'll notice IC 716 and
the
muting transistor(s) that follows. Back to page 116, there seems to be
enough forward bias on Q716 and Q717 .(676 volts) to possibly mute the
output if there were any input to amplify.

So in light of all these observations, do I just replace IC706? It's about
$30 but I'm wondering if there's some muting going on behind the scenes
that
can be contributing to this problem.

Thanks for your reply.
--
David Farber
David Farber's Service Center
L.A., CA




The .676 at the base of the muting transistors is certainly enough to be
considered a symptom. You've tried a reset, yes? If the receiver had been
told at some point that no speakers were connected, then all channels might
just be muted. Which brings the question, does the headphone jack work? Many
modern receivers include a switch in the headphones jack specifically to
mute the speakers as soon as the headphones are plugged in. In typical HK
fashion, there does not appear to be any speaker relays in this thing, not
with a quick glance at page 121 anyway, so if you have not already looked in
that area it might not be a bad idea...
You could look at the junction of R854 and R855 to check the mute drive
which I suspect is active, or just short B-E on one of the muting
transistors...
Of course there could be an actual circuit malfunction, and if this is
confirmed to be the case, frankly without LOTS of patience and a willingness
to lose money on the repair, and lacking boards to swap to narrow it down, I
would be tempted to just pull the plug on this one.
Of course this assumes you have eliminated the usual suspects - the various
power supplies, and so forth.

A sign of old age I suppose, but I'm less and less willing to break a sweat
on these. The lack of serviceability on the vast majority of late model
receivers is almost criminal. The manufacturers don't care that they are
difficult to assemble, since they are using cheap Chinese labor anyway, they
don't care that it's tough on the warranty servicers, and they certainly
don't want them fixed out of warranty. The trend has always been there of
course but it's really got much worse the past 10-20 years.

Mark Z.