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Default Vintage Pioneer SX-838 receiver - UPDATE

When I put the top and bottom back on the unit and plugged in all the
various RCA plugs and speaker wires and 300 ohm antenna, the same
problem reasserted itself, the left channel bugged out.

Then I pulled the top and bottom and set the unit up on its side and it
has been playing all day without a hitch.

So I am thinking the problem is either heat related or position related.

As far as position related goes, this time the unit is standing up on
the opposite side as before, so I think the problem is heat related. As
long as the top and bottom are off, the left channel does not go out.
That makes a problem because as long as the problem does not assert
itself with the top and bottom off I cannot poke and prod and measure.

Got it!

I will simply leave the top and bottom off and put the unit on its side
and live with it.
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Mr.T Mr.T is offline
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Default Vintage Pioneer SX-838 receiver - UPDATE


"Readily Visible" wrote in message
...
As far as position related goes, this time the unit is standing up on
the opposite side as before, so I think the problem is heat related. As
long as the top and bottom are off, the left channel does not go out.
That makes a problem because as long as the problem does not assert
itself with the top and bottom off I cannot poke and prod and measure.


Of course you can, that's when you use a hot air gun and "freezer" spray. In
fact heat related issues are usually the easiest of intermittent faults to
find IMO.

MrT.


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Arfa Daily Arfa Daily is offline
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Default Vintage Pioneer SX-838 receiver - UPDATE


"Mr.T" MrT@home wrote in message
u...

"Readily Visible" wrote in message
...
As far as position related goes, this time the unit is standing up on
the opposite side as before, so I think the problem is heat related. As
long as the top and bottom are off, the left channel does not go out.
That makes a problem because as long as the problem does not assert
itself with the top and bottom off I cannot poke and prod and measure.


Of course you can, that's when you use a hot air gun and "freezer" spray.
In
fact heat related issues are usually the easiest of intermittent faults to
find IMO.

MrT.



I agree. Most probably heat *and* position related. As I said originally,
look for bad joints on items screwed to the heatsink. When the thing is the
right way up, heat expansion on a bad joint may well cause it to become
intermittent. When it's on it's side, the change in mechanical force on that
joint, could easily keep it *good*, electrically.

Arfa


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Mark Zacharias Mark Zacharias is offline
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Default Vintage Pioneer SX-838 receiver - UPDATE

"Readily Visible" wrote in message
...
When I put the top and bottom back on the unit and plugged in all the
various RCA plugs and speaker wires and 300 ohm antenna, the same
problem reasserted itself, the left channel bugged out.

Then I pulled the top and bottom and set the unit up on its side and it
has been playing all day without a hitch.

So I am thinking the problem is either heat related or position related.

As far as position related goes, this time the unit is standing up on
the opposite side as before, so I think the problem is heat related. As
long as the top and bottom are off, the left channel does not go out.
That makes a problem because as long as the problem does not assert
itself with the top and bottom off I cannot poke and prod and measure.

Got it!

I will simply leave the top and bottom off and put the unit on its side
and live with it.




I will often take a BIC pen or a wooden chopstick or the like and push,
poke, tap around etc to help find intermittent connections.

BTW, the fact that you may have tended to the relay contacts does not
eliminate the relay completely. This is where the chopstick or whatever
plastic object you have comes in handy.

Mark Z.

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martin martin is offline
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Default Vintage Pioneer SX-838 receiver - UPDATE

On May 27, 5:57*am, Readily Visible wrote:
When I put the top and bottom back on the unit and plugged in all the
various RCA plugs and speaker wires and 300 ohm antenna, the same
problem reasserted itself, the left channel bugged out.

Then I pulled the top and bottom and set the unit up on its side and it
has been playing all day without a hitch.

So I am thinking the problem is either heat related or position related.

As far as position related goes, this time the unit is standing up on
the opposite side as before, so I think the problem is heat related. As
long as the top and bottom are off, the left channel does not go out.
That makes a problem because as long as the problem does not assert
itself with the top and bottom off I cannot poke and prod and measure.

Got it!

I will simply leave the top and bottom off and put the unit on its side
and live with it.


Gosh this is one you want in front of you, I have been reading the
posts to this and thought I would throw in my half pennys worth. When
I first read your description I was going to say get out freezer
spray, but the fact it started working for hours after cleaning relay
contacts - makes me suspicious of them still. Maybe others will have
same experience, if they are not big meaty relays often cleaning is
not good enough, and replacement is only sure fire way of making good
repair. If you are feeling adventurous you could bridge across relays
- to eliminate them from being the problem, until you have found
fault. Remember it is a hazard if left open no kids near please.
Regards Martin


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Default Vintage Pioneer SX-838 receiver - UPDATE

martin wrote:
On May 27, 5:57 am, Readily Visible wrote:
When I put the top and bottom back on the unit and plugged in all the
various RCA plugs and speaker wires and 300 ohm antenna, the same
problem reasserted itself, the left channel bugged out.

Then I pulled the top and bottom and set the unit up on its side and it
has been playing all day without a hitch.

So I am thinking the problem is either heat related or position related.

As far as position related goes, this time the unit is standing up on
the opposite side as before, so I think the problem is heat related. As
long as the top and bottom are off, the left channel does not go out.
That makes a problem because as long as the problem does not assert
itself with the top and bottom off I cannot poke and prod and measure.

Got it!

I will simply leave the top and bottom off and put the unit on its side
and live with it.


Gosh this is one you want in front of you, I have been reading the
posts to this and thought I would throw in my half pennys worth. When
I first read your description I was going to say get out freezer
spray, but the fact it started working for hours after cleaning relay
contacts - makes me suspicious of them still.


But it was on its side with the top and bottom off when it played for
hours after cleaning the relays. I was reluctant to put it back in its
proper place until I was sure it was playing okay. It could be that the
relays were fine and the fact that it was open and on its side may have
been the factors that allowed the left channel to play for hours without
bugging out.

Maybe others will have
same experience, if they are not big meaty relays often cleaning is
not good enough, and replacement is only sure fire way of making good
repair. If you are feeling adventurous you could bridge across relays
- to eliminate them from being the problem, until you have found
fault.


I was waiting for the left channel to drop out to try that on the spot
with a jumper to see if that kicked the bad channel back in, but I may
have to jumper it and reassemble it to tell for sure as it only seems to
bug out when the case is fully assembled and it is properly oriented.

Remember it is a hazard if left open no kids near please.
Regards Martin

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John Keiser John Keiser is offline
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Default Vintage Pioneer SX-838 receiver - UPDATE

Or run the temporary relay jumper wires out of the case through an air vent
so you can open/close to test the theory with the case closed.


"Readily Visible" wrote in message
...
martin wrote:
On May 27, 5:57 am, Readily Visible wrote:
When I put the top and bottom back on the unit and plugged in all the
various RCA plugs and speaker wires and 300 ohm antenna, the same
problem reasserted itself, the left channel bugged out.

Then I pulled the top and bottom and set the unit up on its side and it
has been playing all day without a hitch.

So I am thinking the problem is either heat related or position related.

As far as position related goes, this time the unit is standing up on
the opposite side as before, so I think the problem is heat related. As
long as the top and bottom are off, the left channel does not go out.
That makes a problem because as long as the problem does not assert
itself with the top and bottom off I cannot poke and prod and measure.

Got it!

I will simply leave the top and bottom off and put the unit on its side
and live with it.


Gosh this is one you want in front of you, I have been reading the
posts to this and thought I would throw in my half pennys worth. When
I first read your description I was going to say get out freezer
spray, but the fact it started working for hours after cleaning relay
contacts - makes me suspicious of them still.


But it was on its side with the top and bottom off when it played for
hours after cleaning the relays. I was reluctant to put it back in its
proper place until I was sure it was playing okay. It could be that the
relays were fine and the fact that it was open and on its side may have
been the factors that allowed the left channel to play for hours without
bugging out.

Maybe others will have
same experience, if they are not big meaty relays often cleaning is
not good enough, and replacement is only sure fire way of making good
repair. If you are feeling adventurous you could bridge across relays
- to eliminate them from being the problem, until you have found
fault.


I was waiting for the left channel to drop out to try that on the spot
with a jumper to see if that kicked the bad channel back in, but I may
have to jumper it and reassemble it to tell for sure as it only seems to
bug out when the case is fully assembled and it is properly oriented.

Remember it is a hazard if left open no kids near please.
Regards Martin



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Default Vintage Pioneer SX-838 receiver - UPDATE

John Keiser wrote:
Or run the temporary relay jumper wires out of the case through an air vent
so you can open/close to test the theory with the case closed.



Good one, Jim. I like it.

It has been playing on its side with the top and bottom off for over 10
hours now and no problem. If I do as you suggest and I find it is not
the relay I guess I will have to resort to heating up the amp board and
output trannies to see if I can replicate the problem with the case and
bottom off. I have a cheap hairdryer that I bought to use as a heat gun
on the job when I need one. That should be sufficient to heat things up
enough to trip the problem if the problem is heat related.
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

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.
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

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.


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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

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,
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


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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

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


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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

On May 28, 8:45*pm, Readily Visible wrote:
Readily Visible wrote:


(snip)


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.


(snip)

It sounds like a speaker relay problem. I had an AM/FM receiver of
the same vintage that dropped one channel randomly (always the same
one) but it would sometimes come back if you "bumped" the volume up to
"too loud" and then back before the speakers/ears protested to much. I
had already changed the volume control - not a fix. At this point I
suspected the speaker relay contacts, i.e. higher speaker voltage
spike breaking down an intermittantly open relay contact. I
unsoldered the relay very carefully, removed the plastic case even
more carefully (these things are not designed to be user maintained!),
cleaned the contacts (fine abrasive paper plus switch cleaner) and put
it all back together. Problem solved, no more drop-outs.
Hope this helps.
Cheers,
Roger
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

Engineer wrote:
On May 28, 8:45 pm, Readily Visible wrote:
Readily Visible wrote:


(snip)

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.


(snip)

It sounds like a speaker relay problem. I had an AM/FM receiver of
the same vintage that dropped one channel randomly (always the same
one) but it would sometimes come back if you "bumped" the volume up to
"too loud" and then back before the speakers/ears protested to much. I
had already changed the volume control - not a fix. At this point I
suspected the speaker relay contacts, i.e. higher speaker voltage
spike breaking down an intermittantly open relay contact. I
unsoldered the relay very carefully, removed the plastic case even
more carefully (these things are not designed to be user maintained!),
cleaned the contacts (fine abrasive paper plus switch cleaner) and put
it all back together. Problem solved, no more drop-outs.
Hope this helps.
Cheers,
Roger


Thanks, Roger, but I don't think the speaker relay is at fault. As I
posted earlier in this thread, when the left channel dropped out I
shorted the soldered terminals going into the speaker relay and got
nothing. I wish it were the speaker relay, but it definitely is not. I
bypassed it when the channel was out and got nothing.
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

In article , 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.


Chopstick will work nicely especially if its plastic. You could have also tapped
the output relay and avoided attaching leads.

greg


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William Sommerwerck William Sommerwerck is offline
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

If I understand it correctly, poking the tranny (something I would never
do!) caused the corresponding channel to drop in and out.

So... are you ready to swap trannys?

(I'm a bit confused. Does this unit actually use driver transformers? It's
hardly a recent model, but I thought driver transformers had disappeared a
few years before this series.)


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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

In article , "William Sommerwerck" wrote:
If I understand it correctly, poking the tranny (something I would never
do!) caused the corresponding channel to drop in and out.

So... are you ready to swap trannys?

(I'm a bit confused. Does this unit actually use driver transformers? It's
hardly a recent model, but I thought driver transformers had disappeared a
few years before this series.)



I think he meant trany istor.

Used to have bad transistors in some Tek scopes that ran hot.
over time the internal connection would become unstable and poking
would bring it back. Probably just the solder joint.

greg
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Arfa Daily Arfa Daily is offline
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???


"GregS" wrote in message
...
In article , 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.


Chopstick will work nicely especially if its plastic. You could have also
tapped
the output relay and avoided attaching leads.

greg


Is it just me, or is this getting (made) ridiculously complicated ? It's an
old amplifier with a well defined repeating intermittent problem, that can
be provoked pretty much at will, most of the time, by poking with a
chopstick. It has now reached the point where different thread respondents,
are offering the same advice. Just solder up all the joints on all the
devices attached to the heatsink, and if that doesn't work, swap the suspect
transistor with the corresponding one from the other channel. if the problem
moves to the right channel, then you know it's the transistor, so just stick
a new one in. If neither of those things cure it, then you need to apply
some more detailed fault finding. This sort of problem is a fundamental
'bread and butter' one that you would put the workshop junior on. I don't
mean to be unkind, but if you are having this much trouble tracking down a
straightforward problem like this, I'm not sure that you should actually be
inside it in the first place ?

Arfa


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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

Readily Visible wrote:
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,


On heavy parts - especially heatsinked ones - it's entirely possible for
a good looking joint to be dry internally. I'd desolder all the pins &
resolder them from scratch.


--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

William Sommerwerck wrote:
If I understand it correctly, poking the tranny (something I would never
do!) caused the corresponding channel to drop in and out.

So... are you ready to swap trannys?

(I'm a bit confused. Does this unit actually use driver transformers? It's
hardly a recent model, but I thought driver transformers had disappeared a
few years before this series.)


He means transistors, not transformers.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------


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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

GregS wrote:
In article , "William Sommerwerck" wrote:
If I understand it correctly, poking the tranny (something I would never
do!) caused the corresponding channel to drop in and out.

So... are you ready to swap trannys?

(I'm a bit confused. Does this unit actually use driver transformers? It's
hardly a recent model, but I thought driver transformers had disappeared a
few years before this series.)



I think he meant trany istor.

Used to have bad transistors in some Tek scopes that ran hot.
over time the internal connection would become unstable and poking
would bring it back. Probably just the solder joint.


That'd be my diagnosis too. Happens all the time with heatsinked parts,
because the pins don't get hot enough to 'wet' properly when they go
through the wave-soldering machine at the factory.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

In article , Bob Larter wrote:
GregS wrote:
In article , "William Sommerwerck"

wrote:
If I understand it correctly, poking the tranny (something I would never
do!) caused the corresponding channel to drop in and out.

So... are you ready to swap trannys?

(I'm a bit confused. Does this unit actually use driver transformers? It's
hardly a recent model, but I thought driver transformers had disappeared a
few years before this series.)



I think he meant trany istor.

Used to have bad transistors in some Tek scopes that ran hot.
over time the internal connection would become unstable and poking
would bring it back. Probably just the solder joint.


That'd be my diagnosis too. Happens all the time with heatsinked parts,
because the pins don't get hot enough to 'wet' properly when they go
through the wave-soldering machine at the factory.



Thats what happens to boards, but I'm not saying that. Its
the connections INSIDE the transistor that were going bad.
Poking the transistors vibrated the internal connections.
The only way to fix the problem was to install new transistors.
These were the ones in the 5000 series for the vertical and horizontal
drives.

greg
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

GregS wrote:
In article , Bob Larter wrote:
GregS wrote:
In article , "William Sommerwerck"

wrote:
If I understand it correctly, poking the tranny (something I would never
do!) caused the corresponding channel to drop in and out.

So... are you ready to swap trannys?

(I'm a bit confused. Does this unit actually use driver transformers? It's
hardly a recent model, but I thought driver transformers had disappeared a
few years before this series.)


I think he meant trany istor.

Used to have bad transistors in some Tek scopes that ran hot.
over time the internal connection would become unstable and poking
would bring it back. Probably just the solder joint.

That'd be my diagnosis too. Happens all the time with heatsinked parts,
because the pins don't get hot enough to 'wet' properly when they go
through the wave-soldering machine at the factory.



Thats what happens to boards, but I'm not saying that. Its
the connections INSIDE the transistor that were going bad.
Poking the transistors vibrated the internal connections.
The only way to fix the problem was to install new transistors.
These were the ones in the 5000 series for the vertical and horizontal
drives.


I wasn't arguing with you about the Tek parts, just talking about the
likely cause of the OP's problem. ;^)

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???


"Bob Larter" wrote in message
...
Readily Visible wrote:
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,


On heavy parts - especially heatsinked ones - it's entirely possible for a
good looking joint to be dry internally. I'd desolder all the pins &
resolder them from scratch.


--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------



Which makes my point exactly ...

Arfa


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Default Vintage Pioneer SX-838 receiver - UPDATE -- FIXED???

Arfa Daily wrote:
"Bob Larter" wrote in message
...
Readily Visible wrote:
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,

On heavy parts - especially heatsinked ones - it's entirely possible for a
good looking joint to be dry internally. I'd desolder all the pins &
resolder them from scratch.


Which makes my point exactly ...


Indeed!

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------


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Default Vintage Pioneer SX-838 receiver - UPDATE


"Readily Visible" wrote in message
...
When I put the top and bottom back on the unit and plugged in all the
various RCA plugs and speaker wires and 300 ohm antenna, the same
problem reasserted itself, the left channel bugged out.

Then I pulled the top and bottom and set the unit up on its side and it
has been playing all day without a hitch.

So I am thinking the problem is either heat related or position related.

As far as position related goes, this time the unit is standing up on
the opposite side as before, so I think the problem is heat related. As
long as the top and bottom are off, the left channel does not go out.
That makes a problem because as long as the problem does not assert
itself with the top and bottom off I cannot poke and prod and measure.

Got it!

I will simply leave the top and bottom off and put the unit on its side
and live with it.


I had this problem once a long time ago with another brand amp, a Proton, I
think. Turns out I was putting a screw back in the wrong place. It was
just long enough that when it was placed on its feet, it shorted to the
circuit board.


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