[chuck]

On Mon, 16 Jul 2012 12:23:23 -0700, Jack wrote:

Jack wrote:
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...

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.

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.


Mark,

The problem returned while playing an FM station. I clicked the Phono-1
button and then the FM button again and the channel came right back.
Something new to delve into.

When the left channel went out again, applying slight pressure to the
push button circuit board brought it back. I also noticed that when the
channel was out, touching the metal prong in back that connects the
preamp to the main amp for that channel produced a 60hz hum.


As Mark said, the switches on the front are a major problem and need
to be cleaned. I would buy a can of Deoxit 5 and spray it into all
the switches and work the push buttons in and out. Chuck