Discussion in 'Exclusively Sansui' started by sajjad amer, May 18, 2018.
I have one of these on my bench, so I am getting familiar with it.
As for the protection flashing, you need to figure out if the circuit is activated by the amps. Measure DCV at TP31,32 on F-5693(Power Amp) with respect to ground. They should be
~ -0.6V when working properly. If it is driven, then the problem is the amps, not the protection ckt.
Accessing the protection pcb is not a treat. It is buried on the back panel.
At least you can manage to adjust the offsets without much trouble.
I agree with you but I decided to send it to the expert after all this as I felt out of my depth.
Thank you for your input I appreciate it
Thanks Rick - useful information as I didn't know what voltage to expect there - TP31/32 are actually on F-5639 (Protection Board)
These points are wire terminals marked as 31, 32 on the power amp pcb (F-5693) , right above C51,52, connected to pins 149,49 on the limiter pcb (F-5694)
Ok thanks - I just found what you are directing me to (I had been looking at the schematic not the board diagram) - thanks again.
This AU-X901 has now arrived at casa Hyperion for a little holiday.
10 minutes on the bench and after a bit of adjustment, we get the happy twang of the speaker relay closing.
Oh my Goodness, so what was I missing ? I am grateful
Let's just say the DC offset adjustments were very far from what they should be.
That is great you do not have to tear the back off to get at the protection ckt, which I think would be a real PITA
I found that Offset adjustments on this model are touchy and drift around. Multiturn precision pots would help out.
The bias adj is very touchy as well. I managed to get them in the 12-17mA range, but one touch and they jump. I let the unit warm right up. I did not run it as they say in the manual.
I found if I measure across the emitter resistors center to center I could switch between normal and integrated to fine tune the zero/null adjustments.
John do you have any means to measure the balanced output at the speakers?
What I noticed is how well the amp seems to control the bass. I have a cheap open baffle test speaker(6x9), the bass extension seems to be more and better defined with this amp.
This was just a first quick pass, I will be able to take a proper look tomorrow as local domestic matters are intervening just now.
It is a real beauty, and in lovely condition, just needs a small external clean up to be literally in showroom condition.
That's a good question, best I can manage is a (battery powered) digital multimeter across a dummy load.
John, you do have a one of this, don't you?
This AU-X901 is now packed and ready to be returned to Sajjad, just a few adjustments, a clean up, including some 'Sansui glue' removal, no more protection mode, and it's now sounding wonderful.
It was interesting for me to see the '901 as I had never seen one before. Also interesting for me to compare it to my '701 which is a firm member of my collection as I have decided I like the accurate (almost clinical) presentation it gives. The '901 seems to have somewhat richer bass presentation than the '701 even when everything is set to 'flat' - but I may change my mind about this as I'm going to put the '701 into the system for a while.
One bit of daft procedure was noted in the Sansui Service Manual for the AU-X901, in that there are two adjustments for cold-ground DC offset which are both monitored at the speaker terminals. Obviously they interact with each other and being in different parts of the amplifier could get in a bit of a mess as you adjust one down, and the other one up to compensate - they could both hit the extremes of adjustment before being set correctly. The AU-X701 doesn't suffer from this as it doesn't have the adjustment!
The solution is to measure at R47 on each of the Control Amp outputs, pin 123 (Left) and pin 126 (Right) while adjusting VR6 (L&R) to null the cold-ground DC offset.
I have received the amplifier and it works perfect. I cannot thank you enough @Hyperion , I could never have pulled this off without you.
My pleasure Sajjad - it is a beautiful example of this model, your work on it was very good as well.
For me the rest was pretty easy.
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