[Arny Krueger]

"Richard Crowley" wrote in message


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.

Sometimes the bad connection is inside a part, particularly coupling
capacitors. Then the bad part needs to be replaced.