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AU-X11 Repair attempt.

R

Rumnarv

Member
I got another dirty one. This is a Japanese domestic 100V unit so I will be using a step down converter. I'm hoping this will be pretty close to the AU-X1 because I can't locate a service manual for the AU-X11.

When I got this thing I was a little bummed about the condition and was wondering if I bit off more than I can chew. The unit was shipped in a very sturdy box but wasn't protected with plastic. The cardboard rubbed off the screening on the face where the model number is and a couple of spots around the controls. The back panel is bent causing the cover to not seat correctly and the wood corners are crushed. If I can get this thing back to sounding great I'll replace the sides.

Inside its not too bad, the transformer has some light surface rust and its a little dusty, not too bad. I powered it up with the converter and dim bulb tester and all I get is the blinking protection light and a bright dim bulb tester. It looks like its not functional. I'll start working on this one board at a time replacing the have to parts and testing the questionable ones. I'm hoping that the factory outputs and FETs are ok. We'll see.

Here are some pics.









Step down transformer


dim bulb tester


I'll start working on this once I finish the AU-717 and QRX that I'm working on.
 
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The AU-X11 is nothing like the AU-X1. It's a great amp, though. You can get the schematic from my friend, Isao. He has all the Sansui manuals and provides excellent copies for a very reasonable price.
http://www.obsinc.us/Dep_VOVS_Literatures.htm
You either have blown output transistors or a short in the power supply.
 
dr*audio said:
The AU-X11 is nothing like the AU-X1. It's a great amp, though. You can get the schematic from my friend, Isao. He has all the Sansui manuals and provides excellent copies for a very reasonable price.
http://www.obsinc.us/Dep_VOVS_Literatures.htm
You either have blown output transistors or a short in the power supply.
Click to expand...

Thanks for the link! I'll have to get in contact with him because there isn't a listing for the AU-x11 one that site.
 
Thanks for the info!

Ive been on the amp8 site before. Good Info! Google Translate seems to work ok. I did find out that the AU-X1 and AU-X11 are very different especially in the output section. The X1 has 6 output transistors per channel and the X11 has 4 per channel. I really wish I could find a service manual for this amp, Ive been looking pretty hard without success. Hopefully this weekend I can get some time to finish my 717 so I can start work on this thing.

Question, Ive been looking for a way to test a FET but have been unable to find one. Is it like testing a transistor with the diode check?
 
X11 Service Manual

Wally1955 said:
Hello Sir
i got the same problem as u with the AU-X11 also cant find a service manual for the machine did u find inbeteen a service maual ?If so it would be great if u can send me readable copy ill pay for all expenses ty in advance
best regards
Wally
Click to expand...

I will ask around about one this weekend.
I can PM you and let you know how it goes.

R6
 
Time to bring this post back from the dead. I've been looking at this amp in my closet since I found it and now I think its time to fix it.

While watching some football I started disassembly on the living room floor.







Once I got it apart, you can see that this thing has some pretty heavy shipping damage. That's going to be fun to straighten back out.









I got the amp modules out, it appears to have the original outputs.







Upon closer inspection and further testing, I found one channel to be in good shape. The other one I wasn't so lucky. All 4 outputs are shorted. While looking over the board with the blown outputs it looks like a couple of the resistors have been shorted as well. One thing strange about these 2 boards is that one has black flag caps and the other doesn't. It doesn't look like the board without them has been repaired because all of the solder joints look factory. Maybe that board was replaced at one time??



The Good Channel..


The Blown Channel


Look at the resistor in the center, looks suspect to me..


Anyways that where it sits now. With the help of this forum; I'm making a parts list to replace the electrolytic and black flag caps, out of spec resistors, trimmers, transistors, and the outputs for both boards. One problem I'm running into is replacement outputs in a TO-3 case. They are non existent. I saw a post where someone used TO-3P outputs so thats what I'll plan to use as replacements. I know the Sansui purest will object, but to protect the function and sound of this amp its my only option. It also doesn't require major modification to the heat sink, just have to insulate the leads where they pass through it and possibly drill the holes a little larger. I will hang on to the 4 good outputs just in case I run into another original set then I can switch them back.

The one major problem I do have is that I can't locate a service manual for this model. If anyone has one I will compensate you for your time to scan and email a copy :). I've compared these boards to the AU-X1 and they are totally different, so that service manual won't work. Fun Stuff!!!
 
So I got to work of this thing this past weekend. I got a bag full of parts from Mouser to rebuild both amp boards as well as replace the outputs. Here are some pics!







Finished the board that was defective. 3/4 of all the transistors were blown as well as almost all of the larger resistors. I ordered 1w flameproof replacements and they were 1/4 of the size of the originals. Worried about them overheating I ordered 2w resistors and they were much larger than the others which surprised me. If they were right in the middle they would have been perfect. I decided to use them anyways and they fit pretty good. I replaced all electrolytic caps, trimmers, Black Flags, zener diodes, red dot diodes, and out of spec resistors.



Time to mount the TO3P replacement transistors in the place of the original outputs. I didn't want to mount them with the leads going through the factory holes because I didn't want to take the chance of them shorting out. Also Ive read that the TO3P doesn't dissipate heat as well as the metal cased TO3. 't do this I didn't want to modify the heat sink so I could go back to the stock outputs (when I find them). To do this I got a sheet of copper, 16 gauge in thickness. I cut and drilled it to fit into the stock heat sink.



To attach the leads of the outputs I found some 15 pin terminal strips that fit almost perfectly. All I had to do is remove 3 of the pin sections and drill holes in their place and modify the pins to accept the transistor leads.





The plan is to wire the transistors around the bottom of the heat sink to make the connections on the back.





Both sides done.



Hopefully this setup will work. I'll cut another strip of copper to put on top of the outputs to help dissipate the heat. I'm waiting on terminal strips to rebuild the back with new parts so the original parts can be easily reinstalled once I find stock outputs.
 
AU-X11 Repair attempt

Yes, fantastic, well thought out repair. I don't think that that the qualifier "attempt" is appropriate. I have a few observations and questions. It seems that despite following the AU-X1 and having similar specifications that the AU-X11 is a very different amplifier rather than a refinement on the unstable X1 as I used to believe. So here it goes:

1. It seems that the original output transistors on the X11 (NMA/NMC 1718) were different than those of the X1 (Sanken 2SA1068N/2SC2493N) or the AU 919 (NMA/NMC 1012). The NMA/NMC were Sankens too, I believe, and may have represented Sansui proprietary labeling labeling rather than Sanken's. Any big differences here or implications in these choices?

2. What benefit, if any, comes with having the AU-X1 have 6 output transistor sets per channel and the AU-X11 4? Why did they do that?

3. It seems that the black flag capacitors were used only in the AU-919, -X1, and -X11 integrated amplifiers (I know that the BA-F1 has them too). Does anyone know if these are these found only in Sansui amplifiers? Why were the developed i.e. size or other considerations?

I'm sorry, I can't stop thinking about design choices and changes even though I don't even know diddley squat about electronics. Regards to all. My feelings will not be hurt if this post is completely ignored.

Marc
 
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mjs1 said:
Yes, fantastic, well thought out repair. I don't think that that the qualifier "attempt" is appropriate. I have a few observations and questions. It seems that despite following the AU-X1 and having similar specifications that the AU-X11 is a very different amplifier rather than a refinement on the unstable X1 as I used to believe. So here it goes:

1. It seems that the original output transistors on the X11 (NMA/NMC 1718) were different than those of the X1 (Sanken 2SA1068N/2SC2493N) or the AU 919 (NMA/NMC 1012). The NMA/NMC were Sankens too, I believe, and may have represented Sansui proprietary labeling labeling rather than Sanken's. Any big differences here or implications in these choices?
Click to expand...

I think Sansui were trying things out, and may have been 'guided' by the manufacturers production 'run size' for producing these special transistors. Transistor fabrication was coming along in leaps and bounds at this time, and new processes we producing more consistant devices as a result. (Agree the word 'attempt' is no longer appropriate here - there is some excellent work taking place. ;))

mjs1 said:
2. What benefit, if any, comes with having the AU-X1 have 6 output transistor sets per channel and the AU-X11 4? Why did they do that?
Click to expand...

Just for division of output current AFAIK.

mjs1 said:
3. It seems that the black flag capacitors were used only in the AU-919, -X1, and -X11 integrated amplifiers (I know that the BA-F1 has them too). Does anyone know if these are these found only in Sansui amplifiers? Why were the developed i.e. size or other considerations?
Click to expand...

I think Sansui decided that if they used polystyrene capacitors in those locations, the benefit from polystrene being the best performing dielectric would be realised in the quality of sound output while fulfilling the preservation of stability in the amplifier output stage.

mjs1 said:
I'm sorry, I can't stop thinking about design choices and changes even though I don't even know diddley squat about electronics. Regards to all. My feelings will not be hurt if this post is completely ignored.

Marc
Click to expand...

Always a pleasure to respond to your posts when I can, but feel there are AK people who can add information or answer these questions better than myself.
 
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Rumnarv - Great job on the copper mounting plate for TO3p output transistors

I believe the black flag caps were also used in selected Kenwood/Trio amps too (L-07MII?) - Also the Sansui AU-719 has a few as well as the AU-819.
 
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I believe the black flag caps were also used in selected Kenwood/Trio amps too (L-07MII?) - Also the Sansui AU-719 has a few as well as the AU-819.[/QUOTE]

You are quite right on your beliefs .All X19 had them. Also LO7's not only mkii's.
 
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