[Fred[_12_]]

"Adamfarber" wrote in message ...

'Fred[_12_ Wrote:
;911336']"Adamfarber" wrote in
message ...-

'Fred[_12_ Wrote:-
;911292']"Adamfarber" wrote in
message ...--

David Nebenzahl;911263 Wrote:-
On 6/13/2010 12:56 PM Adamfarber spake thus:
--
Hi Mark, I unhooked everything and hooked up a speaker to one
of-
the-
outputs and listened to FM and I still heard the him. Thanks,-
Adam---

The "him"?
Oh, you must mean the "hymn".


Whoops, meant HUM, thanks, Adam---

Most likely a cap in one of the low voltage supplies has failed,
feeding unfiltered
DC to a regulator which cannot maintain smooth output voltage
because
the input
is going to zero 120 times a second.

You have to be a technician with troubleshooting skills, experience
with AV receivers,
test equipment and service information to fix this. Assuming
that's
not you, the unit
needs to go to a Yamaha warranty station for repair (Yamaha's
warranty
stations have
access not just to service manuals but also to confidential service
bulletins, and more
importantly they have access to the technical staff at Yamaha, which
is
the only really
competent technical staff in the business). I can call Allen at
Yamaha, give him the
model number, and he'll tell me what the problem is and how to fix
it
because he and his
staff know their equipment that well.

Obviously, I work for a Yamaha warranty station. That's the only
company we still do
warranty audio work for, because it's the only one with a staff
that
knows a damn thing
about their product. Well, them and McIntosh, but there are no Mac
dealers around here,
so they don't figure they need a warranty station here (Reno, NV).

Fred


Hey Fred, thanks for the post. I am somewhat handy, if someone
could
narrow down which part(s) may be suspect I will replace them so any
help you could give me would be GREAT! Adam--

I'll check the service manual & bulletins when I get back to work (I'm
out with
the flu at the moment, and don't know for sure when that will be;
sometime in
the next day or three) and see if I can give you any worth while
advice. Some
models are damn near impossible to take apart and get back together
without
the manual. There can be 20 or more cables that have to be unplugged
and
then plugged back in to the right socket on the right board on
reassembly, just
to get to the board(s) you need to work on. I'm assuming you want to
try a
shotgun approach and just replace every cap that could be causing the
problem.
It'd take a 'scope to figure out what cap *is* the problem.

Watch this thread; I'll post again when I have some information for
you.

Fred

Shall do Fred, thanks again for trying! Adam

Hi Adam,

Finally got back to work today, and had a look at the service manual.

First, you want to check the + & - voltages to the output stage. To do this,
you'll need a Digital Multi-Meter (DVM). You want to check the voltage from
chassis ground to the collectors of any two adjacent output transistors in the
power amp with the unit powered up. Be careful not to let the meter probe
touch anything else while doing this, or you'll get a big arc and blown fuses or
worse. The exact voltage will depend on your line voltage and the setting of
the 4/8 ohm switch on the rear panel; the range is approximately +/- 40V to
+/- 70V. What's important is that the + voltage equals the - voltage within a
volt or two. If the voltages are not nearly equal, the main filter cap for the
lower of the two voltages is probably bad. Those caps are on the Main (3)
board at the left rear of the unit.

It the unit passes that test, one of the following capacitors is probably bad,
and without a scope the only way to proceed is to obtain replacements for
all of them and replace them all.

On the Power (5) board, in the left front of the unit, mounted on the power xfmr
secondary: C451 & 452, 330uf @ 50V. C453 & 455, 4700uf @ 25V. C458 &
463, 4700uf @ 16V. Lastly, on the Main (3) board previously mentioned, C760
& 761, 100uf @ 50V.

If replacing these caps doesn't eliminate the hum, or if all this sounds way over
your head, it's either off to a warranty station with the unit, or off to the
electronics store in search of a replacement. I would expect repair to cost
between $100 & $200. This is a pretty old unit; the service manual was printed
on paper. These days everything is in PDF on the computer.

Hope this helps,

Fred



--
Adamfarber