Arfa Daily wrote:
"Arfa Daily" wrote in message
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"Mark D. Zacharias" wrote in message
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"Mark D. Zacharias" wrote in message
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"Mark D. Zacharias" wrote in message
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"Mark D. Zacharias" wrote in message
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"Dave" wrote in message
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I have an old Yamaha CR-820 receiver/amplifier that no
longer has any sound output. The meters still show signal
strenght when a tune across the AM/FM bands but I get no
audio from the speakers or the phone jack. No hiss. hum,
carckle or pops. JUst solid dead silence. It isn't worth
sending out for a shop base repair.

Has anyone has a similar problem? Does anyone know where I
can obtain a schematic or service manual?




If it's nothing straightforward like a failed ( rather than
blown ) fuse, then it's most likely that the speaker
protection circuit is operating because of a blown output
stage. I've a vague recollection that this one uses an
output hybrid ( big black "IC" bolted to the heatsink with
type STK-xxx ) and if so, it is likely that this is your
problem. Some of these can be very expensive, and many of
the older ones are now obsolete and hard to obtain. If it is
one of the models that uses discrete output stages, then you
might struggle to get to the bottom of its problems,
particularly without a set of schematics, which again, might
be difficult to find for an item this old. Arfa

The CR-820 uses discrete transistors, but the repair isn't for
newbies - there's fusible resistors inside asbestos tubing
which go bad, usually without any visible clue, and the
layout is hardly service-friendly. Mark Z.

OK, much like the modern Yammy AV amps then ...

Arfa

Well, they aren't flat packs - they're TO-3's - 2SB557 and
2SD427 IIRC. Four-gang (once again, IIRC) tuner, all analog,
silver face, wood cabinet, rectangular metal knobs, and lots of
14 volts lead-lamps which burn out... mark Z.

I was being facetious Mark, and referring to the fact that it's
layout is not very service friendly ...I went to a Yammy training
seminar recently, and the national service manager told us that
the average turnaround time on an AV amp for a Yammy dealer, was
22 days, which was really too long, and could anyone venture a
suggestion as to why this was. I told him that the first 16 days
were spent looking at it sitting on the shelf, hoping that it
would go away. The next 3 were spent trying to work out what the
internal diagnostics were trying to tell you. The next 1 was
spent trying to strip it apart and work out which screw was
still holding it. The next day was spent fixing it and putting
it back together, and the final day was spent either rejoicing
that you could write a bill out for it, or crying whilst
watching all the magic smoke being released again ...!! Sound
about right ? d;~} Arfa

Sound
about right ? d;~}

Absolutely. I just got in an RX-Z9, lightning struck. Can't tell
you how much I'm looking forward to that one...

Mark Z.

Hey Mark

Have you done much with the RX-Z1/DSP-AZ1 ? Have you had any
problems with the 4 pin 5v regs? I've got one in at the moment.
Runs absolutely fine for about 20 mins, then starts cutting out,
back to standby. Re-powers with standby switch, but about 1 second
only. Diagnostic memory says PS Prot : 016 K/L and then some
stuff referring to the processor rev numbers. Don't know about
you, but I have a hard time ever making any sense out of those
Yammy diag messages. " PS " rather than " DC " says power supply
rather than output offset protect, but what is " 016 " trying to
tell me ? I seem to recall that it refers to a percentage error on
a rail, but that there are two different schemes used for the
reference. Today, I went down the path of pulling out the sub psu
board to the point where I could get at it to take some
measurements on all the regs on there. With the meter on peak
hold, I caught the output of IC451 going up to 8.54v just before
it tripped out. Now I reckon that's about 160% up on the correct
5v, so is that what " 016 " is trying to say ? Interested as to
whether you have had anything similar. I've got a replacement
coming tomorrow, so should know within 20 minutes of turn on, but
already, no matter what I charge for the repair, I'm actually
going to be down when you count in all the time to dismantle,
trouble shoot, and reassemble. Without doubt, I'd have to say that
Yammies are among the worst of the current crop of AV amps for
service and repair. They are just not friendly at all in any area
- electronic design, mechanical design and user interface. Arfa

I have had that exact problem on one - and the regulator fixed it
just fine - no other damage done.

I've never bothered to try to decipher those DC error levels. They
are based on 5 volts, as I recall.

Mark Z.

OK, well that's good to know. The reg didn't actually turn up today,
so hopefully tomorrow. You are right that the error figures do
relate to 5v - I can remember the little Japanese guy that lectured
me on it originally, saying so, but his english was not too good,
and I was having enough trouble just trying to stay with that, let
alone the in-depth meaning of what he was actually saying. I
definitely do remember him saying that there were two different
schemes as to how the figure related to 5v though. Shame really, as
he was a very clever guy, and clearly knew these beasts inside out,
but boy, was his lecture hard work to understand, just purely from
the linguistic point of view. And then, of course, we had Mr Beardy in
the class, who stopped the
poor little guy every six sentences, and took him, and the whole
class, off on a tangent about some obscure problem that he'd had 10
years ago, for 15 minutes. I'm sure that you've been there ...

Thanks for confirming my suspicions about the 5v reg - I'll let you
know ! Arfa

Mark

Reg chip arrived. Fitted Friday morning. Still running Friday night,
so I guess we got us a result !

Arfa

Woo-Hoo!

mz