Sansui AU-717 / 517 / 919 sticking volume pot

Discussion in 'Exclusively Sansui' started by lasminit2, Jan 29, 2017.

  1. lasminit2

    lasminit2 AK Subscriber Subscriber

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    Well, as our shared hobby goes, there's nothing much worse than the day your good old workhorse AU-717 (or fill in the blank) develops a case of Acute Volume Pot Seizure. There have been a couple of threads written on this subject, but the results seem inconclusive in some cases, or meandering. (threads naturally wander into cleaning the internals of the sealed Alps pot, etc. This is different)
    So this thread is only for the owner's of amps with sealed Alps pots that are starting to resist turning. Now that I have discovered how easy this fix is, I'd recommend it as soon as the knob feels even a little too resistant. My own 717 had reached the point where knob was slipping on the shaft rather than turning (yep, I checked the set screw), and I started to worry that "forcing" it might cause internal damage.
    There is a good thread in which Echowars and others recommend getting lubricant into the shaft, and it worked perfectly for me, but there are a few details to share. You will, of course need to remove the volume knob (1.5mm allen) but the good news is that no other disassembly is required. The gap where the shaft enters the pot is very tight, and you are going to need a way to flow a lubricant that won't react badly with the old hardened grease from 1977 (or whenever): a very "thin" lube that flows well. That can always be helped by gravity,
    so:

    1) A thin lube that plays well with others

    2) the amp will have to stand up on its rear so that the volume pot shaft is vertical (for gravity and capillary action to distribute the lubricant.

    3) Applying a little heat (as suggested in another thread) definitely helps move the lube along the shaft.

    I recently purchased some Hetman Synthetic "Light Bearing and Linkage Lubricant 13" for use on tuner capacitor bearings (but never, ever on the fins). Whatever you use, make sure it says "compatible with petroleum-based oils". Synthetics are generally thin, easy to flow, and won't break down in this century. This product was really designed for use on musical instruments, especially horn keys, where it is hard to remove 100% of the old lubes. It also has a long, very thin, metal pipette to deliver the oil (just about perfect for this task).

    My 717 has two rear plastic bumpers that make it easy to stand on its back. I think they were supplied with rack ear kits. If you don't have these, I guess a couple of wood blocks should work: just be careful of the delicate parts that could get crunched back there. You could even screw the wood blocks into the rear panel using the pre-drilled bumper holes. (screws are same as side outer case)
    Of course, if your amp is torn down for a rebuild, just arrange it so that the vol pot shaft is pointing toward the ceiling.
    Use a hair dryer to warm it up. I borrowed a very wimpy travel dryer from my wife, and it took forever. I didn't heat it up enough to start melting plastic, just to the point where the volume shaft was a bit hot.
    Then apply the lube around the seam, just a couple of drops. Clean up any that gets on the Alps plastic case with a paper towel. I let it soak in for about 2 hours (a basketball game that, unfortunately, my Tarheels lost. Sigh).
    Next, check for any broken down black, goopy old grease that has seeped out, and clean this off. I then added another drop or two of lubricant, and waited another hour or two.
    Next, I repositioned the volume pot: clean the upper shaft first (alcohol on paper towel) to make sure none of the lube is on there: the set screw has to clamp, and you don't want it slipping. Once the pot is in place, work it very slowly around. You should already feel a big difference. Areas that were especially tight before might need some extra turns, and if it still feels stuck you probably will need another pot from a donor unit.
    This worked so well on my AU-717 that I am amazed to think that this is the way it "turned" when new. The click stops feel much more precise. I hope this works for you, as well.
     
    Last edited: Oct 23, 2017
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  2. Robisme

    Robisme Sansui Enthusiast Subscriber

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    Location:
    Martinez California
    Good post. I will keep it in mind if my AU-719 volume control ever gets stiff. At this time, it still turns nicely.

    Rob
     
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  3. JoshHendi

    JoshHendi vintage audio student Subscriber

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    Location:
    southeastern Washington State
    The pot on my 717 literally just stuck the other day... I am going to try these steps, thanks for the detailed post!

    I just purchased a bottle of the Hetman Light Bearing and Linkage Lubricant 13 on Amazon for $10
     
    Last edited: Jun 8, 2017
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  4. JoshHendi

    JoshHendi vintage audio student Subscriber

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    Location:
    southeastern Washington State
    GREAT results using these steps from the OP :)

    I used a mechanical pick to first remove any build up crud at the base of the shaft, then applied two very light applications of the Hetman's #13 lubricant. After a couple hours and another application, I then was able to sneak in some deoxit.

    The results are fantastic. The pot which was 100% froze up is now moving freely again with nice smooth clicks/steps.

    This is the way to go if your Alps pot is fighting you

    Thx lasminit2
     
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  5. lasminit2

    lasminit2 AK Subscriber Subscriber

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    Glad it worked, Josh!
    If AU owners continue to get good results with this method, it could save a lot of Drilling into those nice sealed Alps pots.
     
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  6. cmike

    cmike New Member

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    Location:
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    This is exactly what happened to my volume pot. How did you remove the volume pot? I am not able to line up the wrench to the screw. I am hitting the volume shaft with the allen wrench but unable to locate the screw.
     
  7. Ronito6

    Ronito6 Super Member

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    1,001
    This type with a long enough shaft to clear the face-plate will work a treat.
    [​IMG]

    Those L shaped ones are too fiddly.
     
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  8. cmike

    cmike New Member

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    Thanks will try and report back!
     
  9. cmike

    cmike New Member

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    Location:
    Chicago
    Just got my volume pot off, my pot was jammed, I had to heat the pot and use a bit of muscle to get it off. Did some cosmetic damage in the process. Using the above mentioned lubricant. noticing a difference already. Thanks everyone for the info and support.
     
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  10. usedto

    usedto Lunatic Member

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    Here's another little tip if you need to lube a control but don't want to sit and wait to keep adding solvent/lube. Cut a small piece of clear plastic tubing that will fit over the stem, stem housing, and mounting threads. Then' just fill the tube and let it soak in. Be sure to put a rag or something under the control to catch anything that runs out. If the stem has a slot like the one in the photo, you can even stick a small screwdriver in the slot and work it while it penetrates. stem lube.jpg
     
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  11. cmike

    cmike New Member

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    Location:
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    This has been a very interesting project. I have always tinkered with electronics, and without a doubt I am novice. Originally I took my AU 717 to a respected audio repair shop and asked then to clean up the amp and replace part as needed. They informed me all that was needed was a cleaning, the volume pot is sluggish because of the grease issue, but they said it works fine. Till 4 - 5 months later when the volume pot seized. With the help of this thread and other website I was able to resolve issue. I now know the volume pot was difficult to get off because it was glued on, the screw was never there, I am assuming they lost screw when they took off the volume pot. Also the screw that holds the volume control box to the frame was loose, resulting in me taking off the vent cover and faceplate, to my surprise I saw enough cobwebs and dust leading to me believe it was never cleaned. What I thought was the volume pot turning was actually the entire volume control box spinning leading to one of the wires detaching from the volume control box. Wire has been soldered on the volume control box, it's securely attached to the frame. I was able to take the screw out of the volume pot for TU 717 and place it in the volume pot for the AU 717. Luckily the volume pot for the TU 717 is secure and spins very well without the screw. I will try a replace the screw later. The amp sounds just as good as it ever did!!
     
    Last edited: Nov 15, 2017

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