"William R. Walsh" wrote in message
...
Hi!

As you are hearing some hum through one channel, this would
suggest that the relay is closing (can you hear it close after a
short delay from switching on ?)

Yes, the relay closes. I have replaced 7C26 just now. The old cap
tested OK per the cap checker built into my multimeter, but the new
caps were cheap and I don't want it causing trouble. I've just found a
47uF 80V cap that is also bad. I don't have that one in my stash of
parts, so I may have to order one. It appears that the heat which
burned the circuit board also dehydrated this cap. Removed from the
circuit, it tests open.

There is soft hum from the working right channel. I have yet to hear
anything from the left channel. When it was playing (through the right
channel only), it was possible to just barely hear distorted music
through the left.

I did not notice any DC voltage at the speaker connections, if that's
an acceptable place to take a measurement. I tested that before I ever
hooked any speakers to the unit.

William

Yes, as long as the relay is closing, you can measure offset at the speaker
terminals, with one slight reservation. In the case that you can hear
nothing at all from the speakers, but you hear the relay close, you need to
make sure that having closed, the relay is actually staying closed.
Sometimes, you can be fooled, as on some designs, the protection relay will
close momentarily, and immediately reopen if there is a fault.

What's the circuit designation of the new cap that you've found to be bad ?

I note you say that you are using the cap checking facility on your
multimeter. What parameter does this measure ? Capacitance maybe ? If so,
and you are aiming to do a moderate amount of repair work, you would do well
to consider investing in an ESR meter, such as the "Blue" version of Bob
Parker's original design, now marketed as an easy to build kit, by Anatek
Corporation in the U.S. Although capacitance readings can be useful, to get
such a reading necessitates removing the cap from the board. Apart from any
other reason, this can be a tedious procedure if there are a lot of caps to
check. However, a much more valid reason for owning one, is that the ESR of
an electrolytic capacitor is, these days, one of its most important
parameters. A lot of modern circuitry - particularly in switch mode power
supplies - relies absolutely on the ESRs of the caps being within tolerance,
and a basic capacitance meter cannot tell you this. I have seen
electrolytics which show no signs at all of heat distress or bung popping,
and which read almost spot on for value, but whose ESR is out of the window.

If I was recommending test equipment on a usefulness basis, then an ESR
meter would be top of my 'must have' list.

Arfa