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....
***** *********
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.
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....
***** *********
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.
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