"David Farber" wrote in message
...
Mark Zacharias wrote:
"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.

Hi Mark,

The mute drive at the junction of R854 and R855 is about 3.5 volts iirc. I
temporarily did short the mute transistor but I still didn't see signal.
Again, there is not much signal coming out of IC706 to begin with.

I looked at the headphone circuit and noticed there is a switch in the
jack
that goes directly back to the uP, pin 16 of IC201 on page 119, labeled
H/P
_IN. I assume this either mutes the speakers or puts the receiver in two
channel mode. But even if the muting was enabled in error, it still
wouldn't
explain why there's no signal passing through IC 706, the electronic
volume
control. You would still need to be able to adjust the volume when using
the
headphones.

This would be much easier if this model had pre-amp out, main in jumpers.
But it doesn't.

I'm leaning toward replacing IC706.

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






But even if the muting was enabled in error, it still wouldn't
explain why there's no signal passing through IC 706, the electronic
volume
control.

Duh... I'd forgotten that... sorry.

I do think I'd look at any Data, Clock, and Chip Enable lines going to that
chip and see if they are active when they are supposed to. I had one just
the other day where the CE line was leaky right through the chip, 450 ohms
to ground. They don't work so good that way...

Mark Z.