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.