[Readily Visible]

Fred wrote:
Readily Visible wrote:
Readily Visible wrote:
Yesterday with the unit on its side and the top and bottom removed,
it played for 10 hours without the problem left channel dropping out.

This was using 16 ohm speakers.

Today I hooked the unit up to 8 ohm speakers, still on its side and
the top and bottom removed, and after less than two hours of play,
the left channel dropped out. It could have been sooner, I set it to
stereo and set the balance to the midpoint. I checked it after about
two hours of play and the left channel was gone.

Here is where it gets pinpointy. First I tried jumping the speaker
relay solder joints and got nothing, so that rules out the speaker
relay as the problem.

Then I got a nice Japanese style pine chopstick and started poking on
the amp board. First, since the bottom was oriented to me, I started
poking all the cold solder joints that I had earlier hot soldered. No
change. The left channel remained dead. Then I rotated the unit,
still standing on it's end and began poking all the trannies,
resistors, coils, caps and whatnot. First time through, nothing.
Then, when I poked the leads of one of those flat trannies screwed
to a heat sink on the left side of the amp board, the left channel
kicked back in.

For those who are really interested, here is a link to the service
manual with parts lists and schematics:

http://www.hifiengine.com/manuals/pioneer/sx-838.shtml (relatively
painless registration required)

The tranny in question is 2SD358 on the left channel side. It is one
of those that drives one of the output trannies. The solder joints
are hard to access, but look to be well soldered, so I am going to
assume, at this point, that poking the leads corrected, for the
moment, an internal fault in the tranny. If the local electronics
supply shop has the NTE equivalent, I may swap it out at some point,
but for now I will just let the unit play to see what may develop.

Wow, just after I posted this, I got up to check the unit. Left
channel has dropped out again so naturally I am going straight to the
2SD358 tranny on the left side.

Here I go, with my exquisite Japanese style pine chopstick...

Well here's what happened. The unit is on the floor and as I lay down
next to it and positioned myself to poke the tranny (damn, that sounds
suggestive!) I hit the power on/off switch and cut the power. I
switched it back on and the left channel started playing. I then
poked the tranny (this is definitely *not* what it sounds like) and
the left channel dropped out.

Well, after a few minutes of poking the tranny with the left channel
playing and the left channel dead, I can't say for sure what is
happening. The left channel is playing now and no amount of poking
this specific tranny makes it drop out. When it does drop out, the
trick of turning the volume up to a specific point kicks it back in.

If it weren't for the fact that the left channel continues to be the
one to drop out after connecting the left preamp output with the
right power amp input and vice versa, I would bet money on the volume
pot.

Well, it's continuing to play without a hitch so far, but at least I
have a suspect.

You need to get some deoxit D5 and clean all the pots and switches,

The left channel continues to drop out even when I switch the right
preamp output to the left power amp input and the left preamp output to
the right power amp input.

That rules out all the switches and pots... which I have already cleaned
with copious amounts of deoxit D5-like substances.

The problem *has* to be after the signal reaches the power amp circuitry.


especially the tape monitor switches and if it has one, external processor
loop switch. You most likely have an oxidized contact somewhere in the
left channel which is being disturbed when you touch the volume control,
causing it to play for awhile until it gets tired and quits again.

Fred