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The flashing Sansui AU-D11

Dave C

Dave C

Super Member
I told a friend I'd take a look at his AU-D11 amp, it fires up and flashes or blinks. I've been told by the guys around town to walk away from it. I'd like to get more information before I do that. I would in the long run like to change out the 8 big caps in the power supply but don't want to move with that before knowing if the outputs are shorted or not and where and what to put in there if they are. I would think I should start trying to get the offset in line and see it it works. Any input from experienced minds here would be appreciated.
 
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When you say flashing, I presume you mean the power/protect indicator on the front panel. If so, the amp is in protect mode, which means there is a malfunction with the driver or output stage. Most likely is bad output transistors, if lucky could be a problem with the driver stage.

I've not worked on this model personally, but from what I've read, the AU-D11 is not an easy amp to work on. While it gets high marks for it's sound quality from those who own one, repair and restoration is not a pleasant process from what has been posted here.
 
The AU D11 was probably the final TOTL amplifier in the 907 series before they pivoted to the Ground-free/X-balanced design. I had one, in fine condition (my profile picture). It sounded great.

Not to be confused with the AU-D11 II which is completely different and the reputed challenges repairing it.

Here is a 1981 NYT article on the AU-D11. Apparently it was the bee's knees of amplifier technology from it's day.
https://www.nytimes.com/1981/05/31/arts/sound-an-amplifier-that-gilds-the-lily.html
 
If you make any changes as a part of your efforts, powering it up on a DBT afterwards is highly recommended. And you might think about updating at least the power supply and power amp sections as priorities ahead of the filter caps if you do move forward with it. Good luck.
 
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The D-11 is one of the better amps by sansui. Do NOT walk away from it. It IS worth the effort! However, if you don't know what you are doing then wait to find someone that does. You should find the right tech here on the karma. Be patient.
 
It is a DC offset issue, I've not traced it down with a volt meter yet though. It seems like if I commit to a rebuild it will be an on going situation jumping from one thing to another. Thanks for everyone's input on it. If a good tech can be recommended I'd take it.
 
spark1 said:
Where did you measure the offset?
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I didn't yet, this amp worked fine but was stored for a few years now it doesn't work, it only blinks. Web research points to offset issues. I'd like to get it checked first before taking anything apart. I can't find enough information on where to measure it though.
 
DC offset is measured at the speakers terminals with dmm on dc scale on mv. It is adjusted by small trimmers in the driver or main amp board , I don't remember now.
 
If it's in protection, dc offset can't be measured at the speaker terminals. You would have to look at the schematic and find an upstream point at which to measure it.
 
You need to find the junction of kR52 & kR53 (0.22Ω 5W) for each channel. These can be found on the F-3265 Main Amplifier board very near the Output Transistors. Best viewed on the underside of the unit, with the OP transistors, and track side of the aforementioned board in view.

When you have found these points - you need to measure each of these points to chassis ground with a voltmeter. Try to adjust the DC offset trimmers (both of these are located on the F-3263 Driver Amp PCB and both labelled 'VR1') to zero the voltage at these points, one channel at a time. The voltage needs to be below around 0.5V on both channels before the protection circuit will allow the speaker relays to close. If you cannot adjust the voltage, then you have damaged components somewhere and this will require expert attention.

The above assumes that all the power supply voltages are correct, with all fuses intact.

I hope this helps, but you should know that this is a very difficult amplifier for a relative novice to deal with, and the help given here is to allow you to acquire the 'more information' you are seeking, (i.o.w - how damaged is this unit?), rather than guiding you in attempting a complete fix.
 
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Hyperion said:
You need to find the junction of kR52 & kR53 (0.22Ω 5W) for each channel. These can be found on the F-3265 Main Amplifier board very near the Output Transistors. Best viewed on the underside of the unit, with the OP transistors, and track side of the aforementioned board in view.

When you have found these points - you need to measure each of these points to chassis ground with a voltmeter. Try to adjust the DC offset trimmers (both of these are located on the F-3263 Driver Amp PCB and both labelled 'VR1') to zero the voltage at these points, one channel at a time. The voltage needs to be below around 0.5V on both channels before the protection circuit will allow the speaker relays to close. If you cannot adjust the voltage, then you have damaged components somewhere and this will require expert attention.

The above assumes that all the power supply voltages are correct, with all fuses intact.

I hope this helps, but you should know that this is a very difficult amplifier for a relative novice to deal with, and the help given here is to allow you to acquire the 'more information' you are seeking, (i.o.w - how damaged is this unit?), rather than guiding you in attempting a complete fix.
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I can do that, I'll post results when I get time to take a look, Thanks.
 
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