Help Again. Au-717 Different Channel Volumes

phantomrose1999

New Member
Hi, initially i had a major buzz with no volume. This was fixed by changing C06 in the low voltage side of the power supply. One cap was faulty, so i changed all the low voltage capacitors (+-34V) in both channels.
NOW! its crystal clear, however the left channel is much louder than the right side. Even when i use just the power amp, driven directly by my TU-717. Every voltage from the power supply is correct. I have adjusted the bias voltage to 20mV, and the output votage to +-5mV per the repair manual. HOWEVER still no joy, the left is much stronger and clearer in volume than the right, which is lower and a bit muffled.
<<<ANY HELP APPRECIATED>>> I have obtained a circuit diagram and repair guide.
 
Ok, I have eliminated the Power amps. When i switch the input connector to the power amp boards, the situation is reversed, so this proved both the driver/power amp boards are fine. I also connected another pre-amp to the AU-717's power amp in connector, and BOTH channels worked fine.

So, the problem appears to be in the pre amp section of the AU-717.
 
OK, time to start eliminating sections.

First, see if any of the TONE CONTROLS make any difference. I find that on these vintage Sansui's there are a multitude of small circuit cards for the different functions and can play a big part in troubles like this. Change all controls and switches (tone, muting - this is has always been a problem - loudness, filters (lo-hi) balance etc.) and monitor the output. If possible, take the top off and wiggle gently the circuit card for functions in the pre-amp section.

Somehow you need to get one more piece of info to narrow this down. We need to see if it's a routing issue - thru a noisy/faulty switch, for example - or a circuit failure.

You may have to meter check voltages to see if the right/left sections are operating identically.

Try all inputs (you can probably skip PHONO) to see if there is any clues.

Paul
 
Hi Phantom,

Yes I agree with Pauls comments about this pre-amp problem with your AU717, pots/switches/caps/transistors are all aging now, sometimes the only way to really 'cure' faults is to do a clean sweep of everything. Heres something, if you have access to a scope or audio signal tracer, trace the lower channel on the pre-out board and track that signal back from there through the pre-amp and check your voltages with a meter as Paul suggested
You might stumble across a crook pot/transistor/leaky cap.
Good luck and let us know what you find :)
Cheers
Glen
 
Well I have fixed it. Got a program called "sigjenny" from the net. This was a PC driven signal generator i used as input to the Amp, Aux input. Using my CRO i traced the different signal volumes in the pre-amp stage to the wires going to the volume control. Wires 9 and 10 on board F-2720. one of them had disconnected from the Volume control (pink and white). This was IT !!! yippie. Now its back to its stunning glory !!!!!!
 
Fantastic! Not only is your unit restored to health, YOU did it!

Lots of satisfaction in doing that.

Paul

PS: Don't forget to remind your significant other - often - about how proficient you are!
 
Alright, way to go there phantomrose! Glad to hear of the succeful outcome to the problem you had. And Thanks for explaining to us what you discovered that caused the problem, very good information. I wonder if I might have anything similar going on with the volume control on my CA-3000 preamp which has a habit of its right channel cutting out from time to time.

The AU-717 ranks very high on my List of favorite Sansui amplifiers. And a strong case can be made that its quite possibly THE most popular amplifier that Sansui ever made. Enjoy. I certainly do enjoy listening to mine. Anyone who bought one new in 1978 certainly got their money's worth with this model.

Regards,

B/F
 
Hey there Phantom, thats great you've solved it! :) I had a feeling it was going to be something stupid like a crook connection etc, did not seem like a component based problem Good on you.
I've had annoying faults with things in the past, and you do go looking for the most complicated thing like crook caps/transisitors etc, when the nasty little pig of a dry joint/broken track is staring you right in the face! lol...
Now you can enjoy a more 'balanced' sound from your AU717 ;)

BEATLEFRED- You could have something similar going on with your CA3000, sounds like a dirty pot/switch or dry joint/bad connection somewhere....I'm getting the urge to drag out my AU919 now and having a listen ;)
Man I wish they let more Sansui gear into this country at the time. Good old 'import restrictions'. :(

Cheers guys :)
Glen
 
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When i was 15 i was quite fanatical about good hi-fi, A friend of mine had money and wanted a good setup. The AU-717 was top dog at the time and i could not believe the specs. when i saw it, driving a pair of Cerwin Vega 15" based speakers it was WOW !! Anyway my friend bought the amp, along with a Nakamichi 680 cassett deck and philips high end turntable. It has taken me 26 years to finally get my own AU-717 and TU-717 tuner. Now for the Cerwin Vegas !!!!

I have a circuit diagram and service manual for the AU-517, 717 and 919 if needed.

I also collect vavle reel 2 reels and radios from the 50's and 60's. Will put up a pic when i get a clear picture.

Bye
 
Glen:

Nice to hear from you, Happy New Year. The CA-3000 volume control is sealed on the inside which makes it more difficult to get in there to see if any dust/filth had infiltrated, though presumably the seal is there in the first place to prevent just that from happening. So, maybe it could be a loose connection-type problem. As Ive mentioned before on the forum, I think the CA-2000/AU-11000/AU-9900 have the best Volume control that Sansui ever made.

B/F
 
Hey there Phantom :)

Looks like you've got a similar bug to me in regards to collecting..hehe ;)
Not only do I collect old Sansui/Pioneer Hifi, but also old valve radios from the 30's-60's I have a small collection of those,and valve b/w tvs-mainly Phllips and Pye, and I do have several Akai reel2reels two of are valve and an old Philips valve one plus another couple too.
I must get some pics and post them on here one day of my collection of relics..hehe :)

Cheers
Glen
 
Hi there Fred, Happy New Year too :)
You're probably right with the CA3000, its more than likely going to be a crook connection somewhere in it, just a matter of tracking it down. Yes don't those Sansui Definition Series have nice volume controls I know as I have a AU-9900. I reckon they're a dam fine looking amp and sound quality also. I'd love to see an AU-20000 in the flesh, reckon it'd be awesome! :D

Cheers
Glen
 
For the sake of Accuracy, the elite Defintion Series title was bestowed by Sansui upon the BA-5000, CA-3000, BA-3000, and AU-20000. The AU-11000, AU-9900, and CA-2000 which came out afterward was known as the Professional Series. The AU-20000 for whatever reasons, was still in the Line for an extra year and so it shifted into the Prof Series group as shown in one of my Sansui brochures. Regardless though, they are all great models, but I will say that the BA-5000 is in a league of its own that the smaller BA-3000 cant compete with nor the AU-20000 in that the AU-20K is basically a combination BA-3000/CA-3000.

B/F
 
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