[Fred[_12_]]

"Zack" wrote in message ...
Fred wrote:


"Zack" wrote in message
...
if you think that is old, I have an AX-630 which drops one or both
channels
intermittently. During the dropout, the audio is low and distorted with
mostly just buzzing. Increasing the volume sometimes breaks through the
distortion and the problem goes away for a time. The unit has an AST
pack, so replacing just the amp (which otherwise sounds great when it is
working) would require new speakers.

Any ideas what might be wrong with it? Reseating the wires external and
internal does not seem to result in a fix. Mostly happens while using
the tuner, a TX-400U - which had a bad solder joint on the output that
was fixed a few years ago.


Hey Zack,

You say it mostly happens while using the tuner. I assume that's because
you mostly listen to the radio. But if it also happens when listening to
other
sources like CD, the problem has to be in the amp. So here's a plan:

First thing to do is attack the switches & controls with Caig De-Oxit D5.
Push button switches often require removal of the front panel so you can
spray de-oxit into the switch where the shaft from the button enters the
switch. Spray and then cycle the switch 8 or 10 times.

This sounds like a good idea.

Pots only need de-oxit if they scratch or cut out when rotated from limit
to
limit. If they're doing that, they need to have the de-oxit sprayed in

The controls are in remarkably good shape and don't have any noise when
rotated. Kudos to Yamaha on that front.

De-oxit is powerful stuff. You don't have to flood the area for it to
work - a
quick blast will do ya if it's aimed right. Given that both channels are
cutting out individually, it's about a 98% chance the de-oxit is going to
solve your problem if you do it right.

But if that doesn't do it, then it's a matter of finding the bad
connection by visual inspection, mechanical shock (a tap here, a tap
there), thermal shock (freeze spray, heat gun), and/or good old fashioned
signal tracing with a
scope or signal tracer while the unit's misbehaving. Comparing the same
point in the bad channel with the working channel will tell you if what
you're seeing or hearing is OK or not.

Keep in mind it's possible the bad connection is inside a transistor or IC
- freeze spray is good for finding that kind of problem.

It really helps to have a schematic so you can see where the signal goes
next if de-oxit doesn't fix it. Given its age, you can probably find the
service manual for your amp on the internet in pdf form, possibly for a
few $ from
one of the many service manual purveyors out there these days. Google is
your friend.

Ironically, Yamaha has since released a DSP amp with the same ID that has
loads of chips and gagdetry my unit does not have. Makes Google harder to
use.

Thanks for the tips, they are something to try!

Zack,

I don't know what Yamaha's policy is concerning service info for non-warranty
servicers; I've been doing warranty work for them since they first went into the
consumer audio business. You might be able to get the service manual from
Yamaha for a few bucks if you wind up needing it. It's worth a phone call or an
email to find out.

Fred