Sansui au-517

The Fuxtor

The Fuxtor

Addicted Member
Howdy all,
Finished recapping an AU-517 last month and all was great. Unit was working well before the recap fwiw... Started noticing that one channel was stronger than the other. Upon checking the balance with the units balance pot, I realized the actual pot was very "dry and scrapey " feeling?
Whipped out the deoxit and proceeded to clean the pot and followed up with deoxit f5 . Fast forward 15 - 20 minutes , check knob ( which was feeling quite silky and smooth) seems almost seized up.... Go through another deoxit round and the pot loosened up and seems better now.
Hook up some tunes and imbalance is still there? I have exercised the preout switch and it had been previously cleaned, along with tape monitor switches and all the usual suspects.
Decide to check with a multimeter...
Hook up the dummy load running a 1000 khz sine wave , compare one channel to the next shows approx 1-2% lower acv on the weaker channel. Hook up the signal directly into main in jacks and run the app ( using my phone's signal generator app) and compare voltages again and find the exact voltages left to right channel , no difference now! So it appears that the imbalance would be coming from the preamp board... What is the likely hood the balance pot has just worn out on the one set of wipers?? The preamp board received new Nichicon caps so that is ruled out now too. Anyway I can ohm out the pot while it is connected to the board ? Will that require surgery?? Something else I may have overlooked??
Charles
 
Just throwing some after thought in here...,
If no cause reveals itself without major surgery, would I be able to attach a resistor to the stronger channel to help balance it out?? Maybe start with a 10 ohm ??
 
There are a lot of things it could be. I've seen bad pots do it. In most cases it's a mechanical problem with the pot. The two wipers aren't synchronize. It can also be a dirty contact anywhere in the signal path. I wouldn't try to balance it with a resistor. That's a band aid, not a fix. An oscilloscope and signal generator is the best way to find it.

- Pete
 
LBPete said:
There are a lot of things it could be. I've seen bad pots do it. In most cases it's a mechanical problem with the pot. The two wipers aren't synchronize. It can also be a dirty contact anywhere in the signal path. I wouldn't try to balance it with a resistor. That's a band aid, not a fix. An oscilloscope and signal generator is the best way to find it.

- Pete
Click to expand...
Thanks Pete, I guess it wouldn't be to hard to probe the preamp board, im guessing in the case the balance pot is bad, a replacement would be hard/ expensive to find??
 
I've been cleaning all the controls and have found a poppy loudness switch... Could this also be a possibility?? I'm guessing a new set of transistors on the preamp board would fix this...?
Would a good cleaning of the volume pot be a worthy task? Which layer is the one to go for? Think I read a post where a hole was drilled very carefully and deoxit was sprayed inside, but only for a certain chamber??
 
Well i figured out the pop noise only occurs when i am using my phone for testing? Tried a cd and nice and quiet... Kinda weird but i noticed the exact same thing on a Marantz 1070 a month or so ago, loudness button made a horrible popping noise then too. I will have to find a different tester me thinks??
As far as the imbalance goes on this au 517, i am not sure if drilling a hole in the volume pot is such a great idea? As it is, the volume control is not noisy . Life goes on!
 
I've seen cell phones do than even if they are not connected to the amp. If it's a sealed Alps pot, I've had good luck drilling them by hand with a small drill bit in a "pin vice." Put a tiny amount of Vaseline on the tip of the drill to catch the chips. Then you can spray deoxit in. Cover the hole with a small piece of 3M electrical tape.

- Pete
 
LBPete said:
I've seen cell phones do than even if they are not connected to the amp. If it's a sealed Alps pot, I've had good luck drilling them by hand with a small drill bit in a "pin vice." Put a tiny amount of Vaseline on the tip of the drill to catch the chips. Then you can spray deoxit in. Cover the hole with a small piece of 3M electrical tape.

- Pete
Click to expand...
Wow, the vaseline trick sounds like a keeper!
Thanks!!
 
It was the volume pot! This unit has 2 long screws keeping the volume chambers sealed, undid one bolt and loosened the other off a bit and i was able to get some openings for deoxit d5 followed by f5 into the guts. Thanks again for all the great advice!!
 
Well, I have to revisit this! I sold this unit to a friend but soon after he was complaining the volume is weaker on one channel! Ok head over and proceed to clean that volume pot again and instruct him to call me the next day and let me know if it's good. Today he calls and says that the imbalance is still happening..... He then tells me that he has the sansui running a cd player into the tape in/outs and also has another receiver connected after looping thru the Sansui. Ok,
He tells me that he normally runs multiple gear this way and even with the Sansui powered down, the signal still passes thru the tape loop . Even having the signal pass thru the Sansui this way, he insists the one channel is lower?? Fwiw he has connected the signal straight into the other gear and states the signals are balanced then....
Anyone have ant insight here???
 
Hyperion said:
Dirty contacts? lost ground? - need a signal generator and an oscilloscope to pin this one down I think.
Click to expand...
Which contacts are you referring to? The speaker relay is new?
 
Last edited:
Ok, just revisiting this with another piece of the puzzle... Haven't had a chance to get this over to my place and probe around with my scope, but for the hell of it I asked him to check the balance while using the phono output, where he states balance is much more even?? Does this pretty much indicate the problem is at the preamp section??
 
With phono being a lower signal, it's possible he has the volume turned up more to get the same level as when using a CD player. Thus wouldn't notice a difference if the volume pot was worn at the more attenuated position. The AU-517 doesn't have the audio mute switch, so hard to test that. Maybe with a source that has a level adjustment.

Or, maybe the tape switches need to be cleaned again?

Rob
 
A quick look at the service manual shows TR 03,04 on the F-2723 EQ board as 2SA726. Those have got to go.

Also TR 03,04 on the F-2720 Tone board are 2sa726. get them gone also. They are known sketchy buggers.

KSA992 are a known good replacement.
 
Robisme said:
With phono being a lower signal, it's possible he has the volume turned up more to get the same level as when using a CD player. Thus wouldn't notice a difference if the volume pot was worn at the more attenuated position. The AU-517 doesn't have the audio mute switch, so hard to test that. Maybe with a source that has a level adjustment.

Or, maybe the tape switches need to be cleaned again?

Rob
Click to expand...
Ya, my buddy is going to drop er off next week, I'll have to give that and the pre/main switch a few more doses just to be sure. Just out of curiosity Rob, did you bypass your new filter caps on your 519? I just reused the originals on this one, but I was wondering if they are even necessary? Was even thinking about clipping them out and testing...
 
UncleBingo said:
A quick look at the service manual shows TR 03,04 on the F-2723 EQ board as 2SA726. Those have got to go.

Also TR 03,04 on the F-2720 Tone board are 2sa726. get them gone also. They are known sketchy buggers.

KSA992 are a known good replacement.
Click to expand...
I should have just replaced these at the get-go, but at least that board isn't hard to get to.... Not like the power supply!! Thanks for subs!
 
I replaced the bypass caps on the AU-717. There were no bypass caps originally on the AU-719, and that's how I left it.

Rob
 
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