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Sansui AU-517 humming

Leestereo said:
The DBT lighting up and the voltage drop indicates that is short in the right equalizer circuit. Can you post a picture of the F-2723 board?
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Thank you very much for helping.
I mostly followed your recommendations in restoring this amp.
must apologise for the big 470uF caps on the equalizer. I had them laying around and was not quite sure of the replacement 470 uF Bipolars I put in were the culprit, so I temporarily put these fat Nichicons in place.
What I did on this board:
- recapping all electrolytics (most of them 10uF 50V audio grades Nichicons UKT series.
- replacing the four fusistors with 82,5 Ohms Yageo 0,25 Watt 1% metal film resistors.
- replacing the VD1212's with 2xN4148 in series
IMG_6337.JPG IMG_6336.JPG IMG_6326.JPG
I hope my pictures are good enough.
Hans
 
Hyperion said:
Check for reversed polarity electrolytics in particular C32 & C34.
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Well, it isn't them as they are installed correctly as are most if not all of the others, as far as I can see. With the extra information you have provided, you are now very close to finding the problem, but with no obvious short circuits and no burnt resistors I am now suspecting semiconductors.

But see if Leestereo (Ben) can see anything.

Well done for sticking with it. :thumbsup:
 
Hyperion said:
Check for reversed polarity electrolytics in particular C32 & C34.
Click to expand...
I also think they are OK. The only thing I noticed was that there were different voltages and colours in the old capacitors. Thank you for staying with me on this one. I certainly will not give up. The sound of this amp (after recap) in the left channel is very promising! I ruined it myself so it must be possible to reverse that. Another thing I was guessing is that the slightly higher voltage ruined a transistor. I already checked Tr16. It had hfe 486. Looks fine to me. Still 17 more to pull.
 
Verify the installation of the 2 x 1N4148 replacements. Also, ensure that the exposed top of the dual diode at D04 does not make contact with the lower control shaft when it is re-installed.

dual diode.jpg
 
Leestereo said:
Verify the installation of the 2 x 1N4148 replacements. Also, ensure that the exposed top of the dual diode at D04 does not make contact with the lower control shaft when it is re-installed.

View attachment 2422013
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:banana:
Hi Leestereo, you nailed it! I took me 5 minutes to take the four VD1212 replacement out and check them. D04 was shorted! Must have happened with soldering the two N4148’s together. I resoldered the four pairs without the teepee formfactor to stay free from the shaft. And also put back the Bipolars since they had nothing to do with the humming.
Now the amp is working extremely well, no noise, no buzz and lots of power. I am going to put it together soon, but first I let it play for a few hours. Thanks a lot for helping.
I have still another question. When I arrive at 11 o’clock position on the volumepot, the protector kicks in. (This is already loud enough to start a war in the neighbourhood.You hear the speakers clipping and the amp goes in protection. Now my speakers are AR15, so they can handle a lot of power. At least 100 Watts.
Is this because I take approximately 2 Volts signal from my CD-player?
Hans:beerchug:
 
When I rebuilt my AU717, formed the diodes into a M, and added shrink tube to both shafts. Just to prevent any accidents esp if I had to poke around on that board during troubleshooting.
 
Good news! Happy you solved it with the help of Leestereo.
Amazing and important to remember that more often then not we introduce the faults. This of course being one that's not so obvious and not detectable with a fast view over.
The fact that you didn't give up made this a happy ending which regularly doesn't happen seeing the amount of unfinished threads on here.
That's what makes the difference!
:trebon:
 
HansVenlo said:
...I have still another question. When I arrive at 11 o’clock position on the volumepot, the protector kicks in. (This is already loud enough to start a war in the neighbourhood.You hear the speakers clipping and the amp goes in protection. Now my speakers are AR15, so they can handle a lot of power. At least 100 Watts....
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The AR-15 speakers are relatively low sensitivity types at 84.5dB/W/m, so it is not unexpected that the AU-517 protection would be activated when playing these speakers at very loud levels. If you want/need higher sound levels using the AU-517, consider speakers with a higher sensitivity spec.
 
My 517 doesn't go into protection but I haven't had the volume past 3 O'clock (and that was very very briefly) as my ears won't allow it nor will the foundations of the house. My diy speakers are about 89dB.
11 O'clock is about as loud as I can comfortably listen to and 8 O'clock is about my usual listening level when pottering around.

Anyway 10 O'clock is enough to drive the cats out of the house when I want some peace,
 
Leestereo said:
The AR-15 speakers are relatively low sensitivity types at 84.5dB/W/m, so it is not unexpected that the AU-517 protection would be activated when playing these speakers at very loud levels. If you want/need higher sound levels using the AU-517, consider speakers with a higher sensitivity spec.
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No I do not think that we need higher soundlevels I was just curious whether this was normal or not. For now I am happy to return a fully refreshed amp to my son.
Thanks to all the beautifull people on AK for keeping these wonderfull vintage amps working!
Hans
 
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HansVenlo said:
No I do not think that we need higher soundlevels I was just curious whether this was normal or not. For now I am happy to return a fully refreshed amp to my son.
Thanks to all the beautifull people on AK for keeping these wonderfull vintage amps working!
Hans
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Just to give a quick update: DC was to high on direct mains. Adjusted it and a small adaptation on Bias and now it does not come in protection at high soundlevels. Can recommend Leestereo’s mods to everyone. It makes the 517 better than the original.
Hans
 
HansVenlo said:
Just to give a quick update: DC was to high on direct mains. Adjusted it and a small adaptation on Bias and now it does not come in protection at high soundlevels. Can recommend Leestereo’s mods to everyone. It makes the 517 better than the original.
Hans
Click to expand...

Lessons learned:
Always go slow on a recap.
Check your work regularly.
During testing: always use a DBT
When problems are sorted out: set DC and Bias before connecting to full mains
If you can: always avoid the shotgun method.
Don’t keep messing around, start a systematic search and measure and compare.

And last, but very important:
Ask for help on AudioKarma, never give up on old gear, you will be rewarded with fine sounding equipment in the end!
I thank everyone on AK for helping out and good suggestions!
Wish you all the best for 2022!
 
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