I have very little experience with solid state amp cicuits (I usually play with valves), but I am trying to fix a friends amp anyway.
It's a:
SANSUI AU-101
The problem was some distortion in the right channel.
I have narrowed the problem down to the power amp section, which thankfully looks very simple, and is on a seperate PCB.
As far as I can tell, the electrolytics are fine.
I dont know how to test the transistors properly, but they also seem ok.
Could the problem be in the power supply (which is on the same PCB)?
I think I could get along ok if I had a schematic, but I can't find a free one on the net.
Any help or tips will be apreciated, as I said I'm no expert.
It's a:
SANSUI AU-101
The problem was some distortion in the right channel.
I have narrowed the problem down to the power amp section, which thankfully looks very simple, and is on a seperate PCB.
As far as I can tell, the electrolytics are fine.
I dont know how to test the transistors properly, but they also seem ok.
Could the problem be in the power supply (which is on the same PCB)?
I think I could get along ok if I had a schematic, but I can't find a free one on the net.
Any help or tips will be apreciated, as I said I'm no expert.
No Luck
A have been looking around a lot, but still no luck with a schematic.
However, what was interesting, was that most of the sites that I did find which related to the Sansui AU-101, were all compaints of the same, or similar problems.
Also, none of the advice given to these people on the net seemed to help in the least.
I think I may have picked up on some sort of decieving symptom. It's a problem which seems sympler than it realy is.
I must have visited at least 7 or 8 sites, where poeple complained about distortion in the right chanel. Though aparently no other problems.
Have any of you perhaps done any repair on this amp, or even encountered this problem? any feedback will be apreciated.
A have been looking around a lot, but still no luck with a schematic.
However, what was interesting, was that most of the sites that I did find which related to the Sansui AU-101, were all compaints of the same, or similar problems.
Also, none of the advice given to these people on the net seemed to help in the least.
I think I may have picked up on some sort of decieving symptom. It's a problem which seems sympler than it realy is.
I must have visited at least 7 or 8 sites, where poeple complained about distortion in the right chanel. Though aparently no other problems.
Have any of you perhaps done any repair on this amp, or even encountered this problem? any feedback will be apreciated.
Raphael Shaw said:
Raphael,
I don’t think it's the power supply. Both channels would be affected. What makes you think it's the power amp? Also, don't assume the electros are fine, the amp is too old. I think mid '70's.
Same goes for the transistors. Measuring them is the only way to know and even then they can be faulty in-circuit.
So, not an easy task but lets try anyway.
Could you make a small list of the transistor numbers on the output board?
I' asking because I might have a similar schematic at hand.
/Hugo
Hi Raphael,
I do not trust the small electrolytics at all in those older amps. They are not expensive, so just replace them in the amp section while you are getting the numbers for Hugo.
If the unit has pre out and main in jacks, substitute another preamp output into the amp. You may be chasing a fault in the wrong section.
Some 2SC458's were bad production runs (small signal transistor). Watch for those.
-Chris
I do not trust the small electrolytics at all in those older amps. They are not expensive, so just replace them in the amp section while you are getting the numbers for Hugo.
If the unit has pre out and main in jacks, substitute another preamp output into the amp. You may be chasing a fault in the wrong section.
Some 2SC458's were bad production runs (small signal transistor). Watch for those.
-Chris
Thanks again.
The amp doesn't have pre out or main in jacks, but there is only one pair of screened wires conecting the pre amp board and the power amp board. So I un-soldered them, and tested the pre out with another amp, It's fine. I also fed another signal into the power amp, and I get the same distortion. So the problem is definately in the power amp.
Thanks for the tip Chris.
I hope my previous post makes sense to you hugo.
The main transistors are C1364's. There are four of them, and the middle leg is lifted (not used). One of them looks a little different which makes me think it might have been replaced before.
There are also quite a few C1364's around the circuit, and two A640's.
The A678's I mentioned, are in an odd shaped green package, but still resemble transistors, but I've never seen them before.
Jonathan, I did get your e-mail, and I have e-mailed you my postal adress.
Thanks a million. I hope it works out.
The amp doesn't have pre out or main in jacks, but there is only one pair of screened wires conecting the pre amp board and the power amp board. So I un-soldered them, and tested the pre out with another amp, It's fine. I also fed another signal into the power amp, and I get the same distortion. So the problem is definately in the power amp.
Thanks for the tip Chris.
I hope my previous post makes sense to you hugo.
The main transistors are C1364's. There are four of them, and the middle leg is lifted (not used). One of them looks a little different which makes me think it might have been replaced before.
There are also quite a few C1364's around the circuit, and two A640's.
The A678's I mentioned, are in an odd shaped green package, but still resemble transistors, but I've never seen them before.
Jonathan, I did get your e-mail, and I have e-mailed you my postal adress.
Thanks a million. I hope it works out.
FWIW THis was my recent experience repairing my au-101
The amp was given to me as dead.
Visual inspection showed a burnt out resistor off one of the cdc9000-1c drivers so I replaced the resistor. I removed the cdc9000 and found it was faulty. I replaced it with a BD140.
The amp now produced sound but the left channel had distortion.
I then began swaping the small electrolytic caps between channels, none of which solved the distortion.
I then began swaping the transistors between channels and as usual it was the last transistor swap which revealed a faulty 2sc1060 output transistor. Replaced it with a 2SC1398R and all is well.
Hope this helps...
Andy
The amp was given to me as dead.
Visual inspection showed a burnt out resistor off one of the cdc9000-1c drivers so I replaced the resistor. I removed the cdc9000 and found it was faulty. I replaced it with a BD140.
The amp now produced sound but the left channel had distortion.
I then began swaping the small electrolytic caps between channels, none of which solved the distortion.
I then began swaping the transistors between channels and as usual it was the last transistor swap which revealed a faulty 2sc1060 output transistor. Replaced it with a 2SC1398R and all is well.
Hope this helps...
Andy
A problem arrived to me with a Sansui A117 amplifier and a Sansui cassette tape recorder. No sound or distorted.
I found that its origin was the same for both. There are RC decoupling circuits, C being an electroytic; the resistors have either completely changed of value or were open circuits. It is very easy to localise these resistors as they are mounted lift up from the board. They did not show any trace of damage but may be of poor quality. I suggest you check every decoupling circuit before changing anything else.
I found that its origin was the same for both. There are RC decoupling circuits, C being an electroytic; the resistors have either completely changed of value or were open circuits. It is very easy to localise these resistors as they are mounted lift up from the board. They did not show any trace of damage but may be of poor quality. I suggest you check every decoupling circuit before changing anything else.
i have recently aquired a Sansui AU-101 amp, it has some distortion in the right channel, however it is worse when the volume knob is between 2 and 8, any quieter or louder and the distortion seems to disappear.
When using the phono input, both channels are heavily distorted.
Any suggestions as to how i could fix this problem would be appreciated.
When using the phono input, both channels are heavily distorted.
Any suggestions as to how i could fix this problem would be appreciated.
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