[Mark Zacharias]

wrote in message
...
On Jun 1, 8:52 am, Bob Larter wrote:
Arny Krueger wrote:
"Richard Crowley" wrote in message
ez

So sending an audio transient into the amplifier does
something that restores the signal path. My suspect list
would be: solder joints, capacitors, resistors.

Agreed. This is the sort of problem that often goes away after someone
goes
through and reconditions every solder joint in the machine.

As we both no doubt know, the failure mechanism is that an insulating or
semiconducting oxide or sulphide film forms in some signal or supply
path,
which has a very low break-over voltage. The path usually involves a
soldered joint that has either cracked in use, or was defective all
along,
but took years to fail.

Applying enough voltage to "punch though" the insulating film, will
create a
temporary signal path, which eventually gets interrupted again by
corrosion.

A hot, tinned soldering iron in skilled hands, is applied to every
soldered
joint, with a little flux and solder being applied where needed to
ensure a
good soldered joint. Sometimes it is is necessary to remove the existing
solder with a solder pump, and resolder the joint completely.

Ayup. That's exactly what I'd do, starting with the heatsinked parts.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

Back in the day I replaced a fair number of TO-220 case power
transistors that would open the base lead when they warmed up. Does
that Pioneer use any of those?

G²



Pioneer used TO-220's for drivers in this model. Also, the SX-838 used
flat-pack output transistors, some of the first ones. 2SC2525 and 2SB755 as
I recall; certainly they were of that type.

Impractical and unnecessary to resolder all connections - there are simply
too many.

These models really didn't suffer from solder problems in the small-signal
circuits. Power supply and amp driver cards are another matter.

Once again, controls and switches - and those notorious Sanyo blue coupling
capacitors - should be at the top of the list of possible culprits.


Mark Z.