Blown Left Channel on Pioneer SX-727

[Polar Bear]

Hey guys, I just had to share this with you guys and I cut and past this from another audio group, and couldn't believe the advice was given to this guy who was asking if his SX-727 was salvageable, read on....
Polar Bear

_______________________________


This might not be the best place to post this thread, but i've read enough posts here to see that a good portion of the membership exhibit excellent core knowledge. Any thoughts would be appreciated.

I have a (1973) Pioneer SX-727 that seems to have lost its left channel. On the evening of "burn-out" the system started producing the characteristic scent of burning electronics. The unit still produced sound but after a bit of time (after the smell dissipated) i noticed the loss of the left channel (not easily recognizable as this set-up has four speakers oriented kitty-corner in a square room). I unplugged the right channel speaker outputs -- and turned the balance all the way over to "L" -- and the resultant sound was distorted, scratchy, and all fuzzed out beyond recognition. Switching speaker outputs I see that this holds true on all of my left channel outs; "A" "B" and "C".

I'm only guessing here, but are there two separate amps that power each channel, and if so, can they readily be replaced. Or, could my loss of channel be attributed to some other entity.
What do you think?



J. Vigne
Unregistered guest

Posted on Tuesday, June 08, 2004 - 10:19 pm:
After 30 years of use the internal components have simply worn out. Most likely the values of a few bias resistors have drifted and the capacitors are no longer capacitating (yeah, I made that up, but the caps are shot). When this happens the output transistors fry. And if I remember correctly the 737 had what were caled Darlington Block IC (integrated circuit) outputs. Personally, I can't believe it has lasted this long.
This is not what you want to hear (you know what's coming already, don't you?) but at this point in time it is not worth fixing. You will find it very difficult if not impossible to find a shop that has not culled the schematic for this reciever from their files years ago. No schematic, no fix. Bias levels cannot be set properly and values of common components like resistors and caps can't be guessed at. More than likely when the smoke appeared it meant not only fried outputs but more than likely a fried circuit board. There is no way to replace that now days.
If I were you, I would thank the Pioneer for 30 years of service and head out to buy a new unit. If I remember correctly once again, that was only 35 watts per channel and it sold for less than $299 in 1973-4. That means it has cost $10 per year to own this reciever. It is time to retire the SX-737. If you shop carefully you will be suprised at what you can get for your money today. If cost is important look to the used market to find a good value.


John A.
Gold Member
Username: John_a

Post Number: 1345
Registered: Dec-03

Posted on Wednesday, June 09, 2004 - 01:06 am:
J. Vigne is spot-on as usual. Let me just add that there ARE makes where you could repair a 1973 amp and it would be good as new. As J. says, though, one component failure (electrolytic capacitors do dry out and eventually fail) and it can take a whole load of other things with it. You may need to be quite skilled to diagnose the problem, it is unlikely to be simple. That means heavy labour costs. Probably even skilled repairers would advise you to write it off.

If you are thinking of something new to last another 30 years....


Chris Hackbardt
New member
Username: Suspecterrain

Woodland , MI
US

Post Number: 3
Registered: Jun-04

Posted on Wednesday, June 09, 2004 - 09:29 am:
Thanks both,

I didn't think it smelled like there'd be any simple fixes. And yes, i'm very thankful for the length of time this unit has served me (10 years).

I would like to add a minor correction to your comments, J. Vinge: This was the 727, not the 737 -- this one retailed for $399 back in '73 and packed 40 watts per channel. In it's death i would hate if people thought less of my stereo than what it actually deserved.

For what it's worth, i just tagged a model SX-828 (same year, flagship model) for a cool $30 on ebay -- know i'll be flexing 60 watts per channel! That is, if the thing isn't DOA.

Thanks again for the comments - i knew somebody could give me some inferences on what a post mortem on this old girl might uncover.

[EchoWars]

Idiots....

Where was this posted?

With that attitude, virtually 3/4 of AK would be listening to BPC.

[Polar Bear]

Hey there EchoWars......try this link.
Get them straighten out.
Polar Bear

http://forum.ecoustics.com/

[EchoWars]

Closed: New threads not accepted on this page

Threads are closed after less than a month. 'F' it, let em' wallow in their stupidity.

[Polar Bear]

Makes us AK members appricate this group that much more after reading articles like that since we love our vintage gear rather then most folks off the street.
Polar Bear

[SolderIron]

>just tagged a model SX-828 (same year, flagship model) for a cool $30 on ebay -- know i'll be flexing 60 watts per channel! That is, if the thing isn't DOA.

$30+30 shipping arn't bad if it works. Doubt he can get anybody to fix the old one for less.

[glen65]

Originally posted by Polar Bear
Hey guys, I just had to share this with you guys and I cut and past this from another audio group, and couldn't believe the advice was given to this guy who was asking if his SX-727 was salvageable, read on....
Polar Bear

_______________________________


This might not be the best place to post this thread, but i've read enough posts here to see that a good portion of the membership exhibit excellent core knowledge. Any thoughts would be appreciated.

I have a (1973) Pioneer SX-727 that seems to have lost its left channel. On the evening of "burn-out" the system started producing the characteristic scent of burning electronics. The unit still produced sound but after a bit of time (after the smell dissipated) i noticed the loss of the left channel (not easily recognizable as this set-up has four speakers oriented kitty-corner in a square room). I unplugged the right channel speaker outputs -- and turned the balance all the way over to "L" -- and the resultant sound was distorted, scratchy, and all fuzzed out beyond recognition. Switching speaker outputs I see that this holds true on all of my left channel outs; "A" "B" and "C".

I'm only guessing here, but are there two separate amps that power each channel, and if so, can they readily be replaced. Or, could my loss of channel be attributed to some other entity.
What do you think?



J. Vigne
Unregistered guest

Posted on Tuesday, June 08, 2004 - 10:19 pm:
After 30 years of use the internal components have simply worn out. Most likely the values of a few bias resistors have drifted and the capacitors are no longer capacitating (yeah, I made that up, but the caps are shot). When this happens the output transistors fry. And if I remember correctly the 737 had what were caled Darlington Block IC (integrated circuit) outputs. Personally, I can't believe it has lasted this long.
This is not what you want to hear (you know what's coming already, don't you?) but at this point in time it is not worth fixing. You will find it very difficult if not impossible to find a shop that has not culled the schematic for this reciever from their files years ago. No schematic, no fix. Bias levels cannot be set properly and values of common components like resistors and caps can't be guessed at. More than likely when the smoke appeared it meant not only fried outputs but more than likely a fried circuit board. There is no way to replace that now days.
If I were you, I would thank the Pioneer for 30 years of service and head out to buy a new unit. If I remember correctly once again, that was only 35 watts per channel and it sold for less than $299 in 1973-4. That means it has cost $10 per year to own this reciever. It is time to retire the SX-737. If you shop carefully you will be suprised at what you can get for your money today. If cost is important look to the used market to find a good value.


John A.
Gold Member
Username: John_a

Post Number: 1345
Registered: Dec-03

Posted on Wednesday, June 09, 2004 - 01:06 am:
J. Vigne is spot-on as usual. Let me just add that there ARE makes where you could repair a 1973 amp and it would be good as new. As J. says, though, one component failure (electrolytic capacitors do dry out and eventually fail) and it can take a whole load of other things with it. You may need to be quite skilled to diagnose the problem, it is unlikely to be simple. That means heavy labour costs. Probably even skilled repairers would advise you to write it off.

If you are thinking of something new to last another 30 years....

what a bunch of bullshite.

[Polar Bear]

Hey dude, you've miss-spelled " Bullshit "

Originally posted by glen65
what a bunch of bullshite.

[glen65]

Guess I should tell the next person who brings
me a vintage receiver to $hit can it because of a
few dead caps.

[Polar Bear]

Yeah...it's hard to believe there's people still think that way about vintage gear.
Flood me with 70's vintage gear verus today's A/V plastic throw aways.

Originally posted by glen65
Guess I should tell the next person who brings
me a vintage receiver to $hit can it because of a
few dead caps.

[glen65]

Originally posted by Polar Bear
Yeah...it's hard to believe there's people still think that way about vintage gear.
Flood me with 70's vintage gear verus today's A/V plastic throw aways.

Something that pisses me off is the way manufacturers
are throwing around wattage figures any more.
they will stamp 500 watts on the box in 4 inch
print. Then define what it all means in print
you almost need a magnifying see if at all.
Then top it all off with piss poor build quality.
And people wonder why some just want to keep
their old equipment. Duh.. “Gee Wiz I just can’t imagine
why”.

[suspecterrai]

Alright. It's me - i'm the nincompoop who has the problem -- I just came across this website whilst purusing the web for my original post. It is a bunch of garbage that the original thread is dead (http://forum.ecoustics.com/bbs/messages/1/51433.html) as i'd really like to give the idiot with the crap advise a real piece of my mind - or better yet, a swift kick in the pants!

Well, i did pitch that unit (after I striped it of assorted parts) and subsequently bought another SX-727.

...Looks like i should get the "caps" replaced, right off, eh? What should i expect to pay, $100? Any other thoughts?

[suspecterrai]

I little digging around found an associated thread that puts the number at a couple hundred bucks - now if i can just find a reputable shoppe to take my unit to...

http://www.audiokarma.org/forums/sho...d.php?t=140017

[markthefixer]

Originally Posted by suspecterrai

Alright. It's me - i'm the nincompoop who has the problem -- I just came across this website whilst purusing the web for my original post. It is a bunch of garbage that the original thread is dead (http://forum.ecoustics.com/bbs/messages/1/51433.html) as i'd really like to give the idiot with the crap advise a real piece of my mind - or better yet, a swift kick in the pants!

Well, i did pitch that unit (after I striped it of assorted parts) and subsequently bought another SX-727.

...Looks like i should get the "caps" replaced, right off, eh? What should i expect to pay, $100? Any other thoughts?

Yes, WELCOME to AK................

Come on over to the Pioneer forum, and tell us what is wrong with your currently sick unit!!

If you do the labor yourself, I would (just off the top of my head) expect that you could get the caps for under 20 bucks, maybe even shipped for that.

Usually to get a receiver back from the ravages of old age, the contacts are cleaned with deoxit, the pots are deoxited and faderlubed, and the electrolytic caps replaced. Sometimes remounting the power transistors with fresh thermal compound / grease is a good precaution. Then the bias and offsets for the power amp are set back to spec. Of course a good physical cleaning goes without saying... For Pioneers, checking / resoldering the heat stressed solder joints is always a wise investment of time. From that point onwards it depends upon the original unit. YMMV

[markthefixer]

Originally Posted by suspecterrai

I little digging around found an associated thread that puts the number at a couple hundred bucks - now if i can just find a reputable shoppe to take my unit to...

http://www.audiokarma.org/forums/sho...d.php?t=140017

Well, you can always ship it to our Wizard EchoWars (Kansas City). You will get back a unit in tip top shape.

Otherwise there are a lot of choices in Michigan and the area, it's sort of AK's unofficial hub.