Sansui AU-11000 low volume right channel

Discussion in 'Exclusively Sansui' started by redrooster, Jul 16, 2017.

  1. redrooster

    redrooster who was that masked man?

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    geraldton western australia
    When I don't use my Amp for a few days, I sometimes have to flick the mute switch up and down a few times for the right channel to work properly. Now the right channel sound has gone permanently low, no matter how many times I flick the mute switch up and down. There is also an intermittent crackling sound that appears sometimes, but only when the amp has no input? Ive tried DeOxiting the Mute switch and even used a hypodermic needle to try and get the DeOxit into the right spot.(without success, by the looks) Does anyone happen to know if there is by chance an easy way of cleaning this mute switch, other than taking the faceplate off to de-solder the switch, then take it apart and clean it? Im guessing there isn't an easy way but I know theres some geniuses lurking around AK, so I thought I should at least ask first before diving in head first. LOL Im thinking the crackling sound might be a separate issue, like a leaky transistor? but Ive replaced all the transistors with modern equivalents about 4 years ago, all except for TR11,2sc735. TR13,2sa562. on both sides of the driver board? Any ideas, suggestions welcome.
     

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  2. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Need to isolate the problem. Do you have a source with adjustable volume, if so dis-connect the amp pre amp with the switch and feed the mains directly using the source with adjustable volume set at minimum to begin with. If volume now equal inspect and clean the separated connect switch (or leave it in the separated position and use a set of rac jumpers across the input/output terminals. report back for next installment :)
    -Lee
     
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  3. redrooster

    redrooster who was that masked man?

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    TE="Overundr1, post: 10705034, member: 50093"]Need to isolate the problem. Do you have a source with adjustable volume, if so dis-connect the amp pre amp with the switch and feed the mains directly using the source with adjustable volume set at minimum to begin with. If volume now equal inspect and clean the separated connect switch (or leave it in the separated position and use a set of rac jumpers across the input/output terminals. report back for next installment :)
    -Lee[/QUOTE]
    Yay!!!! Good one mate, thankyou so much, those RCA plugs fixed the problem. This is why I need AK! As I get older I get more forgetful. Now I remember having the same problem a while ago and for some reason Ive left the RCA plugs off? But alls well that ends well! :jump:
     
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  4. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Glad to help. I have chased down more faults over the years to that switch than any other Sansui component used in the 70's (other than the c458 transistor). I have also found that in most cases using deoxit or other cleaner on the switch will only give short term results. Nowadays every Sansui piece that comes through the shop that has that switch has the switch removed, dis-assembled and brought back to new condition. As the AK collaborative has yet to find a drop in replacement this is the only way to ensure years of trouble free operation.As a general note, unless you are great at chasing small delicate critters around the bench attempt rebuilding the switch at one's own risk :)
    -Lee
     
  5. redrooster

    redrooster who was that masked man?

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    Bummer!!! It stopped working on that channel again? Its exactly the same as before! Ill have to start looking for a loose or broken wire or something, because it stopped only after I moved the amp around to put the top and bottom covers back on?
     
    Last edited: Jul 17, 2017
  6. moefuzz

    moefuzz Active Member

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    Did you check to see if the flux capacitor was getting correct voltage?



    ?
     
  7. Overundr1

    Overundr1 AK Subscriber Subscriber

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    You need to re-try my first suggestion again with an external volume adjustable source directly into the main in jacks on that AU to isolate whether it is a pre amp or main amp issue. My bet still is on the connect separated switch contacts. Even with the rca cables hooking the pre to the main jacks corroded contacts on the switch will shut off the circuit. Just had my own 9900A (basically the same unit) open on the bench Sunday for a tone control board transistor replacement (transistor went noisy after 40 years go figure) so unit is fresh memory wise if more assistance needed :)
    Switch description---
    The separated connected switch is a two pole triple throw design. The output from the pre-amp section left and right feeds into the switch board through two pairs of wires feeding the start of the switch contact rails. in the connected position the switch feeds that signal through sliding contacts to a second set of contact points that feed another pair of wires leading to the main amplifier input points. When the switch is set to dis-connected worth noting that the input from the pre amp still goes into the switch and then to the rca jacks on the sideplate so if the switch contacts are really corroded you still will get no pass through to the main amp even with rca cables attached. Some folks get so aggravated over this that they permanently connect the pre amp feeds to the rca jacks by jumping the switch board.input/output points, on the other hand taking time to really get after those contacts will resolve the problem for years to come :)
    -Lee
     
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  8. redrooster

    redrooster who was that masked man?

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    Sorry about the delay Ive had some things come up to distract me. I misunderstood your directions last time, anyway I fed the signal from windows media player with adjustable volume directly to the mains, both channels work properly and I could adjust the volume. I have a new old stock pre-mains switch but Ive been dreading putting it in but it looks like the time has come to bite the bullet and do it. LOL P.S. I think I will try and fix the switch in the origonal one first, it looks like its got a tiny ball bearing and maybe a spring so Ill get a neodynium magnet onto it when its coming out. If its too corroded Ill put the new one in then. I tried to upload photos of the NOS switch but no go?
     
    Last edited: Jul 18, 2017
  9. redrooster

    redrooster who was that masked man?

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    Here you go, it worked this time! Pre-mains switch 001.JPG Pre-mains switch 002.JPG I cleaned the excess flux off. Would I have to strip this switch down and clean it because its 40 years old and maybe corroded as well? Is there anything else inside the switch other than the two ball bearings I can see. Like a spring?
     
  10. Overundr1

    Overundr1 AK Subscriber Subscriber

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    :)
    If you decide to take the switch apart there should be two small ball bearings with a spring between them, they are used to allow the switch to stop at each detent position. Carefully lift the retaining ears on the switch and over a well lighted surface ( I have an white piece of cloth that I work over for this) separate the two halves watching for the bearings/spring and the four brass sliding contacts noting which ones went where. The best way to get them clean is to use an ultrasonic cleaning machine as that way you run no risk of bending the contacts, other methods work too. When re assembling be cautious not to force anything or bend the brass contacts or you will be very unhappy.
    Need to remember to photo document this the next time I have one apart, there are other examples in the forum and Kale is the master if you can find his restoration threads for more details.
    Glad the amp is up and running
    -Lee
     
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  11. redrooster

    redrooster who was that masked man?

    Messages:
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    Location:
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    Thanks Lee! I really appreciate the help and advice youve given me. Im going to order an ultrasonic cleaning machine and do this properly! :beerchug:
     

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