[Jack[_11_]]

Mark Zacharias wrote:
"Jack" wrote in message ...
Mark Zacharias wrote:
"Jack" wrote in message ...
Jack wrote:
After a week of playing with no problems, the right channel went out.
It
was the left channel previously. I was dismayed until I remembered
that,
when I reseated the output trannies, I switch them, left for right. I
was further heartened when that same trick of switching off the
speakers
and turning the volume up to max brought the sound back. Since there
are
a pair of outputs in each channel, switching one of them again and
waiting to see which channel goes out next should tell me which tranny
is bad.
After switching back one pair of the output transistors, the PNP's, NEC
B539A's, the problem stayed in the right channel, so I replaced the
right channel NPN, an NEC D287A with an NTE284. It's playing fine at the
moment. I will button it up and consider it fixed until it tells me it
isn't.

Jack

If you have not cleaned the relay contacts yet - you are wasting your
time.

Mark Z.
I cleaned the relays a couple of years ago when I tried to tackle this
the first time. Buffed the contacts with 1200 grit wet/dry sandpaper.
This time I tested the relays by bridging them when the bad channel was
out. didn't help. It wasn't the relay. The problem followed the NPN
output transistor when a swapped them left to right and right to left.


OK, but 1200 grit...Wow. The coating on the contacts must not be too good
anymore...

Oh, well...


I've used 6000 grit in the past and even that was too much.

I'm not sure swapping the transistor really revealed the nature of the
problem. As I'm sure you have seen, often we do something, it seems to fix
the problem, then re-occurs later.

You may very well have both channels cutting out at differnt times.

The right channel never cut out until I swapped transistors. After I
swapped transistors, ONLY the right channel cut out. You have to go on
something and that seemed fairly compelling.


I'm getting in on this late... have you cleaned the front panel push-button
controls? They were NOTORIOUS for cutting out on this model.

Mark Z.


I bypassed all that by using a standalone preamp to drive the power amp.
Problem persisted.

Jack