Hello All,
I hope that this amplifier isn't too new for this forum. It's from the late 70s. So it is more than 30 years old. I have the service data and am wondering what is the most likely component or are most likely components on the driver board to produce this symptom. The output transistors seem ok. It sounds like one of the output transistors isn't operating. (or like in a tube amp when one of the output tubes in push-pull is pulled out). So whatever does the inverting may not be working, or maybe it's an emitter resistor? I'll be examining it later this evening. It's an interesting circuit (16 transistors per channel).

Thanks,

Dave

I remember those when new. I did warranty service for Sansui. A lot of sailors bought them from over seas.
You might start off with swapping the audio output transistors. Next is to look for bad solder connections, all around the pre-amp and driver circuits. If you have a swing needle VTVM you can kick check all those little electrolytic capacitors in circuit. You also can compare working channel voltages to the poor working one. One other thing is the switches. The tape monitor switch gets dirty from lack of use. Give all the switches some exercise, and cleaning if need be. You are lucky that's all that is wrong with it. A good fail burns up a hand full of parts. The output bias diodes are critical. any leak will short an output transistor, then down the line with a cascade failure. Be sure to check those diodes front to back, and back to front.

Edd,
C04 had a swolen top and it measured .05 mf. So I replaced it. It didn't help much. So this is the same as usual. Replace all the 30+ year old dried out electrolytic capacitors, and it should work again.

I'll replace them and let you know what happened.

Thanks,

Dave
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: : : : : : : :Sir DAVE . . . . . : : : : : : :Condsidering that you have walked a good known audio source between both inputs as shown with the :[ RED Round Highlighting ] :at the left top corner of referencing. :AND considering that amp is built all discrete, with cascade direct DC coupling thru the unit and :you have not already popped a string of semis. : : :My “munney” is on the [Yellow Highlighted] electrolytics shown, with one of them probably still retaining a full .1 ufd of capacitance : : : : : :PLUS with one channel normal, you have a perfect “schematic” , to compare the like voltage readings, (which I believe that they :will be quite alike, since your DC biasing thru the amp has not shifted, if you don’t have hot outputs) with the then REAL answer : :then being answered with an oscilloscope in the comparisons of waveforms between like sections, in the case of audio corruption : :via ineffective interstage couling or power supply feed decoupling via the electrolytics. : : :Pss Ess: : :Why did I have this info handy, 'tis because my next door neighbor had the same units, picked up at the China Fleet Club, while :R&R'ing at Hong Kong. : :His recent problem happened to be in his Tuner unit, with a long time obsolete UL703 I.C. having failed in the FM IF strip. . .now : guess who just happened to have one. : :I took no payment, but he is still mowing my lawn for another year, plus, he was additionally one happy camper, driving his big :Wharfdales once again! : : : : : : :73's de Edd : : : : : : : : : :Sansui '517 Series 1 AF Output Stage SCHEMATIC : : : : :

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Edd,
I replaced all the electrolytic capacitors on the driver board and the problem still remains. I'll look for the other capacitors on the other boards you mention.
If I need to I'll dig out the oscilloscope. Maybe there is a problem with the output transistors?

Thanks,

Dave
:

:

: : : : : : : :Sir DAVE . . . . . : : : : : : :Condsidering that you have walked a good known audio source between both inputs as shown with the :[ RED Round Highlighting ] :at the left top corner of referencing. :AND considering that amp is built all discrete, with cascade direct DC coupling thru the unit and :you have not already popped a string of semis. : : :My “munney” is on the [Yellow Highlighted] electrolytics shown, with one of them probably still retaining a full .1 ufd of capacitance : : : : : :PLUS with one channel normal, you have a perfect “schematic” , to compare the like voltage readings, (which I believe that they :will be quite alike, since your DC biasing thru the amp has not shifted, if you don’t have hot outputs) with the then REAL answer : :then being answered with an oscilloscope in the comparisons of waveforms between like sections, in the case of audio corruption : :via ineffective interstage couling or power supply feed decoupling via the electrolytics. : : :Pss Ess: : :Why did I have this info handy, 'tis because my next door neighbor had the same units, picked up at the China Fleet Club, while :R&R'ing at Hong Kong. : :His recent problem happened to be in his Tuner unit, with a long time obsolete UL703 I.C. having failed in the FM IF strip. . .now : guess who just happened to have one. : :I took no payment, but he is still mowing my lawn for another year, plus, he was additionally one happy camper, driving his big :Wharfdales once again! : : : : : : :73's de Edd : : : : : : : : : :Sansui '517 Series 1 AF Output Stage SCHEMATIC : : : : :

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Edd,
The 2670 board is held on to the inside of the back in some mysterious way. What is the secret to removing it to check the capacitors?

Thanks,

Dave
:

:

: : : : : : : :Sir DAVE . . . . . : : : : : : :Condsidering that you have walked a good known audio source between both inputs as shown with the :[ RED Round Highlighting ] :at the left top corner of referencing. :AND considering that amp is built all discrete, with cascade direct DC coupling thru the unit and :you have not already popped a string of semis. : : :My “munney” is on the [Yellow Highlighted] electrolytics shown, with one of them probably still retaining a full .1 ufd of capacitance : : : : : :PLUS with one channel normal, you have a perfect “schematic” , to compare the like voltage readings, (which I believe that they :will be quite alike, since your DC biasing thru the amp has not shifted, if you don’t have hot outputs) with the then REAL answer : :then being answered with an oscilloscope in the comparisons of waveforms between like sections, in the case of audio corruption : :via ineffective interstage couling or power supply feed decoupling via the electrolytics. : : :Pss Ess: : :Why did I have this info handy, 'tis because my next door neighbor had the same units, picked up at the China Fleet Club, while :R&R'ing at Hong Kong. : :His recent problem happened to be in his Tuner unit, with a long time obsolete UL703 I.C. having failed in the FM IF strip. . .now : guess who just happened to have one. : :I took no payment, but he is still mowing my lawn for another year, plus, he was additionally one happy camper, driving his big :Wharfdales once again! : : : : : : :73's de Edd : : : : : : : : : :Sansui '517 Series 1 AF Output Stage SCHEMATIC : : : : :

:
:
:

Edd,
The 2670 board is held on to the inside of the back in some mysterious way. What is the secret to removing it to check the capacitors?

Thanks,

Dave
:

:

: : : : : : : :Sir DAVE . . . . . : : : : : : :Condsidering that you have walked a good known audio source between both inputs as shown with the :[ RED Round Highlighting ] :at the left top corner of referencing. :AND considering that amp is built all discrete, with cascade direct DC coupling thru the unit and :you have not already popped a string of semis. : : :My “munney” is on the [Yellow Highlighted] electrolytics shown, with one of them probably still retaining a full .1 ufd of capacitance : : : : : :PLUS with one channel normal, you have a perfect “schematic” , to compare the like voltage readings, (which I believe that they :will be quite alike, since your DC biasing thru the amp has not shifted, if you don’t have hot outputs) with the then REAL answer : :then being answered with an oscilloscope in the comparisons of waveforms between like sections, in the case of audio corruption : :via ineffective interstage couling or power supply feed decoupling via the electrolytics. : : :Pss Ess: : :Why did I have this info handy, 'tis because my next door neighbor had the same units, picked up at the China Fleet Club, while :R&R'ing at Hong Kong. : :His recent problem happened to be in his Tuner unit, with a long time obsolete UL703 I.C. having failed in the FM IF strip. . .now : guess who just happened to have one. : :I took no payment, but he is still mowing my lawn for another year, plus, he was additionally one happy camper, driving his big :Wharfdales once again! : : : : : : :73's de Edd : : : : : : : : : :Sansui '517 Series 1 AF Output Stage SCHEMATIC : : : : :

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Warren,
Thanks for the advice. I'll try what you suggest, in addition to Edd's suggestions.

Thanks,

Dave
:I remember those when new. I did warranty service for Sansui. A lot of sailors bought them from over seas.
:You might start off with swapping the audio output transistors. Next is to look for bad solder connections, all around the pre-amp and driver circuits. If you have a swing needle VTVM you can kick check all those little electrolytic capacitors in circuit. You also can compare working channel voltages to the poor working one. One other thing is the switches. The tape monitor switch gets dirty from lack of use. Give all the switches some exercise, and cleaning if need be. You are lucky that's all that is wrong with it. A good fail burns up a hand full of parts. The output bias diodes are critical. any leak will short an output transistor, then down the line with a cascade failure. Be sure to check those diodes front to back, and back to front.
:

:I remember those when new. I did warranty service for Sansui. A lot of sailors bought them from over seas.
:You might start off with swapping the audio output transistors. Next is to look for bad solder connections, all around the pre-amp and driver circuits. If you have a swing needle VTVM you can kick check all those little electrolytic capacitors in circuit. You also can compare working channel voltages to the poor working one. One other thing is the switches. The tape monitor switch gets dirty from lack of use. Give all the switches some exercise, and cleaning if need be. You are lucky that's all that is wrong with it. A good fail burns up a hand full of parts. The output bias diodes are critical. any leak will short an output transistor, then down the line with a cascade failure. Be sure to check those diodes front to back, and back to front.
:

Warren,
The diodes seem to be ok. The protection circuit works perfectly. If there is a low frequency rumble like feedback from a magnetic phono cartridge that's too close to the speaker, the relay de-energizes. When the rumble stops, the relay re-energizes. I don't think that's the problem. But, some of the other things mentioned could be. I replaced all the electrolytic capacitors on the board but it made no difference. It still distorts. The symptom is like when one tube is pulled in a push-pull circuit. The sound is there but has a problem. It's not as full as it should be.

Thanks,

Dave
::I remember those when new. I did warranty service for Sansui. A lot of sailors bought them from over seas.
::You might start off with swapping the audio output transistors. Next is to look for bad solder connections, all around the pre-amp and driver circuits. If you have a swing needle VTVM you can kick check all those little electrolytic capacitors in circuit. You also can compare working channel voltages to the poor working one. One other thing is the switches. The tape monitor switch gets dirty from lack of use. Give all the switches some exercise, and cleaning if need be. You are lucky that's all that is wrong with it. A good fail burns up a hand full of parts. The output bias diodes are critical. any leak will short an output transistor, then down the line with a cascade failure. Be sure to check those diodes front to back, and back to front.
::
:

Did you swap the output transistors? One other clue is how warm the output transistors get. If the bad channel gets warmer than the other, it's lack of drive sometimes. As you can see by the print Edd posted, this set can be a bear to work on. If you have a scope, and a signal tracer this will really help. Pull out all the output transistors, then back track the signal and voltages as compared to the working channel. If it's sounding like a tube set not doing its push pull thing, that's about right, it's not. That whole circuit is geared to be for push pull operation. You might even ohm check each transistor in circuit for an open. That seems to be the problem with so many parts in a circuit, one little part goes bad, now try and find it.

Warren,
My customer would not allow me to use the other channel's transistors since they are working. I will have to get a second pair and try them. I found R25 to be 88.5 K ohms instead of 150 ohms and R23 was 278 ohms instead of 150 ohms. So I replaced them and it is still distorted. Yes, I understand what you're asking me to do. I have a couple of scopes here but they're Eico scopes. But I guess they'll work for audio.

Thanks,

Dave
:Did you swap the output transistors? One other clue is how warm the output transistors get. If the bad channel gets warmer than the other, it's lack of drive sometimes. As you can see by the print Edd posted, this set can be a bear to work on. If you have a scope, and a signal tracer this will really help. Pull out all the output transistors, then back track the signal and voltages as compared to the working channel. If it's sounding like a tube set not doing its push pull thing, that's about right, it's not. That whole circuit is geared to be for push pull operation. You might even ohm check each transistor in circuit for an open. That seems to be the problem with so many parts in a circuit, one little part goes bad, now try and find it.
:

Warren,
My customer would not allow me to use the other channel's transistors since they are working. I will have to get a second pair and try them. I found R25 to be 88.5 K ohms instead of 150 ohms and R23 was 278 ohms instead of 150 ohms. So I replaced them and it is still distorted. Yes, I understand what you're asking me to do. I have a couple of scopes here but they're Eico scopes. But I guess they'll work for audio.

Thanks,

Dave
:Did you swap the output transistors? One other clue is how warm the output transistors get. If the bad channel gets warmer than the other, it's lack of drive sometimes. As you can see by the print Edd posted, this set can be a bear to work on. If you have a scope, and a signal tracer this will really help. Pull out all the output transistors, then back track the signal and voltages as compared to the working channel. If it's sounding like a tube set not doing its push pull thing, that's about right, it's not. That whole circuit is geared to be for push pull operation. You might even ohm check each transistor in circuit for an open. That seems to be the problem with so many parts in a circuit, one little part goes bad, now try and find it.
:

I get what your saying about swapping the output transistors. What you can do though, is to check the poor working sides transistors with an ohm meter, then compare with the known good sides transistors. If the reading are the same, the transistors are okay. If not, Then replace. You may have already fixed the problem by replacing those bad resistors, and capacitors. Just an open output transistor now because of that problem.

Warren,
Readings on the transistors from both channels match. The reading from the NPNs are exactly the same, and the readings on the PNPs are the same. The distortion still remains.

Thanks,

Dave
:I get what your saying about swapping the output transistors. What you can do though, is to check the poor working sides transistors with an ohm meter, then compare with the known good sides transistors. If the reading are the same, the transistors are okay. If not, Then replace. You may have already fixed the problem by replacing those bad resistors, and capacitors. Just an open output transistor now because of that problem.
:

Okay Dave, the output transistors are good then. Looks like your going to have to get the scope out, and do some looking at the audio wave forms. You should find the spot where the wave is being clipped. If you have a signal generator, run just a tone though the aux. input jacks. That way you are looking at just a tone wave, not a bunch of junk. Couple both channels together at the input jacks, that way you can see the good wave on the working channel, again compared to the poor working side.

Warren,
By the way. I separated the pre-amp from the amp and used another pre-amp into the main amp and the left channel still distorted. I think if I keep examining components on the board I'll find another faulty one.
I'll lug out the scope later or tomorrow.

Thanks,

Dave
: Okay Dave, the output transistors are good then. Looks like your going to have to get the scope out, and do some looking at the audio wave forms. You should find the spot where the wave is being clipped. If you have a signal generator, run just a tone though the aux. input jacks. That way you are looking at just a tone wave, not a bunch of junk. Couple both channels together at the input jacks, that way you can see the good wave on the working channel, again compared to the poor working side.
:
:

It's now sounding like that big coupling capacitor in the output stage is the one drying up now. I think it's around 4700 MFD.

Warren,
What 4700 mf? where? I replaced every electrolytic capacitor on the driver board. The highest value was 470 mf at 63 volts. I replaced both of them. Where is this 4700 mf capacitor? Is it on another board somewhere?

Thanks,

Dave
:It's now sounding like that big coupling capacitor in the output stage is the one drying up now. I think it's around 4700 MFD.
:

Warren,
This is a Direct Coupled Amplifier. I don't think there are any coupling capacitors. But there are bypass capacitors.
The power supply is working well too. There must be some other drifted resistor that I missed.

Thanks,

Dave
:It's now sounding like that big coupling capacitor in the output stage is the one drying up now. I think it's around 4700 MFD.
:

Never mind about the coupling caps, was thinking about another model Sansui. I have the schematic to your Amp. now. If you would like a copy E-Mail me. It's in the .RAR format. Takes 7-Zip to open it. I have the simple install for that too. Let me know, I can send both.

Warren,
I finally discovered the problem. One of the leads to TR03 was broken under this brown sticky goo used to stabilize the 470 mf capacitors. I think that this is a 70s material that was originally clear but broke down and turned brown. Somehow it attacked the transistor leads. This is a 2SA750. It just says A750 on it.
Look at Edd's post. It has the schematic for the driver board. You will find TR03 on it.
It's good. But the leads are messed up. So I'm going to replace it.

Thanks,

Dave
:Never mind about the coupling caps, was thinking about another model Sansui. I have the schematic to your Amp. now. If you would like a copy E-Mail me. It's in the .RAR format. Takes 7-Zip to open it. I have the simple install for that too. Let me know, I can send both.
:

Good you found the problem. That brown looking poop eats everything it touches. It was used on television sets too. I think it " was " like a rubber cement, would flex just a little. After some years it turned into something else, common to find open foil runs under it, eats the legs off ic's

Warren,
Fortunately that stuff is not on the solder side at all. I'll scrape it away from the board near the new transistor leads and it should be good to go.

Thanks,

Dave
:Good you found the problem. That brown looking poop eats everything it touches. It was used on television sets too. I think it " was " like a rubber cement, would flex just a little. After some years it turned into something else, common to find open foil runs under it, eats the legs off ic's
: