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Sansui AU-717 Deoxit F5 all potentiometers?

C

Crumbs

Member
I got my AU-717 rebuilt but I am experiencing left channel drop out. Adjusting the balance control, or even applying a little pull pressure returns the signal until the knob is adjusted again.

Going to apply Deoxit F5 to that potentiometer but wondering since I know the amp has sat unused for 15-20 years if there is any reason that all potentiometers should not be cleaned with Deoxit F5 even if they are not exhibiting obvious signs of noise?

Clean plan: Tell me if I'm wrong.
  1. unit off
  2. two holes in the top are the way to spray in
  3. rotate knob many times
It is unclear to me if I need to wait a few minutes before turning on the unit (ie delivery liquid evaporates leaving lubricate only) or not.
 
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Did you rule out the rear switch connected-separated? This causes similar symptoms. I had this problem in an AU-517 and ended up disassembling the switch and after cleaning all the tarnish it cured the problem.
 
And I am not a fan of the 'rotate knob many times' thing after DeOxit F5 (NOT D5) application, just a few times is enough, say 5-10 times in my opinion. And for a pot that isn't showing obvious signs of problems, fewer than that.

You need to be gentle with 40 year old potentiometers that are mostly unobtanium. Winding the pot to the full extent of the track multiple times, some actually recommend 50 or 100 times! Whipping it backwards & forwards probably quickly and/or aggressively is not a normal thing for a pot to do, aside from which you will also shorten its life.
I have spoken. You have been warned.
 
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I used some DeOxit F5; it seems to really have cleared it up. The suggestion JoseHH made above probably makes sense but I'm going to leave the switches alone while everything works because I didn't pick up any D5.
 
1. Is it possible to lubricate any of the switches externally? I assume no.
2. Is there a picture guide to AU-717 switch lubrication points?
3. If my balance pot is bad is there a suggested replacement part? Mucking with the balance seems to bring the unit back sometimes but I cleaned it.

The unit was working fine so I didn't lube the switches. Naturally after I put it back together, picked up my tools, and moved everything to put it in place of the existing system it stopped working. Seems to be inconsistent. It initially worked in place yesterday, then this morning it didn't. Moving switches seems to give different outcomes. Sometimes it does with extra noise. Mostly left channel working, right consistently absent. Direct power amp in works both channels.

Plan is to use the DeOxit F5 on the switches.
 
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The Fuxtor said:
Switches are good to go using D5. I think the main difference in the 2 is....
D5 contains 20% D100 deoxidation solution and no lubricant.
F5 contains 5% of the deoxidation solution and does contain a lubricant. Exactly what else is in those 2 I know not.
Click to expand...

That is what I'm trying to figure out, everyone says D5 for switches, but F5 Caig documentation says it can be used on switches. Is there something about the vintage switches, or switches in the Sansui that would prohibit use of the F5? I'd like to use the F5 rather than also purchase a can of D5 to have less cost and less chemicals left over.
 
Observing the unit operation I think the combination of balance, mute switch and volume control are triggering the signal inconsistency.


Anyone think the directions here (http://www.cdkands.com/AU717-7.html) for how to lubricate the volume potentiometer are a bad idea?

It basically suggests carefully drilling a few access holes. I'd probably use a hand drill to do it. Open to other suggestions for how to clean and lubricate the volume knob.
 
Crumbs said:
Open to other suggestions for how to clean and lubricate the volume knob.
Click to expand...
Slacken off (don't remove), the screws holding the 'layers' of the potentiometer together - then, one-by-one open a gap into each layer (just wide enough for the DeOxit tube), and give it a squirt of DeOxit F5, do not use D5 UNLESS you follow it up with F5. Re-tighten the screws (carefully) before any rotation of the pot.

Drilling holes (or burning the holes with a hot pin :yikes:) is unnecessary and risks damaging the pot or leaving plastic swarf inside the pot.
 
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Crumbs said:
That is what I'm trying to figure out, everyone says D5 for switches, but F5 Caig documentation says it can be used on switches. Is there something about the vintage switches, or switches in the Sansui that would prohibit use of the F5? I'd like to use the F5 rather than also purchase a can of D5 to have less cost and less chemicals left over.
Click to expand...
F5 is fine. It doesn't work quite as good. No harm using it
 
Hyperion said:
Slacken off (don't remove), the screws holding the 'layers' of the potentiometer together - then, one-by-one open a gap into each layer (just wide enough for the DeOxit tube), and give it a squirt of DeOxit F5, do not use D5 UNLESS you follow it up with F5. Re-tighten the screws (carefully) before any rotation of the pot.

Drilling holes (or burning the holes with a hot pin :yikes:) is unnecessary and risks damaging the pot or leaving plastic swarf inside the pot.
Click to expand...

That is why I asked the question. If I had done it I was going to turn the unit upside down while creating the hole. Note I found a more thorough reference to your suggestion to partially disassemble.
 
Do I lube and work the volume potentiometer stack again or is there something else I should try?

Status Summary:
I followed the advice above #13 and disassemble in #15 posts to lubricate the volume knob and other controls.
  • within a few hours (< 4 hours) of lubrication it works great (just like it did last time)
  • after sitting for 12+ hours it is as bad or worse
  • symptoms:
    • different channel (now left) dropping out more but in general it fades in and out
    • eventually both channels fade
    • turning volume knob will bring it back to life for less than a full song but operation is inconsistent at best
What was done (this round):
  1. front panel removal
  2. all knob and switch cover removal
  3. 12 mm wrench to take volume potentiometer off panel
  4. tiny phillips screwdriver to loosen the volume potentiometer stack to pry it apart
  5. cleaned/lubricated with DeOxit F5 the following parts using paper towels to cover adjacent surfaces and wipe up excess
    1. volume pot and worked it. sprayed at least twice (maybe 3 times) in all layers, and wiped up excess
    2. lubricated other potentiometers again
    3. lubricated switches (first time)
      1. top-down shot in front through larger metal hole
      2. shot from behind for pre-amp connection switch
  6. worked all movable parts after lubrication
  7. connected and used unit for 20-25 minutes at mostly high volume level (louder than I normally listen)
  8. observed poor unit operation (see symptoms) after sitting overnight just like last time
 
so in post 15133259, #17 above I outlined what I'd tried but I overlooked key observations or details necessary to troubleshoot.

After some troubleshooting I found these core behaviors:
  1. jostling the pre-amp switch as some suggested did not change the behavior or introduce noise as long as I didn't actually change the switch position
  2. the problem occurs whether the signal goes through the preamp or is fed direct to the amplifier input bypassing the preamp
  3. the amp will play longer and generally without any issues at high volume level (read large signal)
  4. after dropping out the signal only returns when volume level increases
    1. mostly due to volume sweep
    2. sometimes muting switch change would trigger signal to return
  5. while mostly in the right channel sometimes the left channel is affected
Assumptions sink good troubleshooting

I'd initially thought the problem had not occurred when directly connected to the amp. I realized it always occurred at lower signal levels, and occurred faster the lower the signal level. Until I removed the assumption that the amp-only operation was fine I couldn't see the solution. I had not replaced the relay yet because as SuperNoob indicated in one of his build threads it looked good. It was the last part in the signal path I had not replaced that was consistent with bad small-signal, good large-signal behavior due to excessive contactor resistance.

Solution
  • I replaced the relay with the part I already had but thought I didn't need to use
    • Omron MY2-02-DC24 was used not the potentially quieter MY4 version (discovered rereading notes but already had MY2 part)
  • Post relay replacement the amp will play consistently at low volume with no noise in volume sweeps
Thanks again to the group, reading posts of others troubleshooting problems helped me realize I was describing the problem wrong and overlooking the source. I should have just replaced it to begin with, it would have saved me a lot of effort.
 
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