Wonky pre/power amp switches, AU-819 & AU-717

[jwc2012]

Hi all,

As the title says, I’ve got an AU-819 and a AU-717 and each has a rear pre/power amp coupling switch that has caused one channel to cut out. Both amps had intermittent cut-outs resolved by fiddling with those switches, but now the channel cut-outs are permanent. I tried spraying Deoxit—no effect.

So now I need to deal with these coupling switches. Any guidance (preferably step-by-step) on how to fix/clean them? Is there an easy and effective way to replace them with another switch?

Also, I would really like to have the 819 restored (recappped, other problematic components replaced). Does anyone have a recommendation for a good tech in Southern California (I’m in Riverside, east of LA and Orange County). Ideally, the tech would have extensive Sansui experience. My old tech, who I liked very much, seems to have disappeared.

Thanks in advance for any help!

JC

 

[nj pheonix]

I'll qualify my comment by saying I have no first hand experience playing with these 2 specifically.
I would try a second deoxit treatment.
Are you exercising the switch after you spray it?(20-30 times).
Sometimes first treatment loosens stuff up and second time gets contacts clean.
Also you should be able to jump the pre out to amp in jacks if its the switch (with an interconnect cable.
Just try not to get too much overpay and wipe carefully any.
Also let dry before powering back on.

 

[jwc2012]

Thanks for the reply.

Yes, I did the whole drill of spraying Deoxit and then really working the switches.

I’ve read elsewhere that Deoxit doesn’t work well to fix these switches, but I tried it to confirm that and cross it off the list of things to try.

I also tried jumpers from the preamp out to the power amp in, and that didn’t work for either amp. Not sure why, but it’s a three way switch so the configuration of the jumping connections may come after the problem area of the switch.

Alternatively, if there is no quirk of how the switch is situated in relation the pre/power output jacks, the fact that jumpers don’t restore the silent channel(s) might point to another problem. Does someone who’s been inside these switches have any insight about this?

 

[nj pheonix]

Try member Hyperion .
I know he's done more than a few of these

 

[Overundr1]

Only way I have been able to keep that switch working without issue is to dis-assemble it. Not way out there on the scale of technical prowess however be warned that mis-handling it will cause irreparable damage. There also are lots of small parts that can and do fly all over the bench if not careful taking it apart.
As a side thought, if you are able to de solder the switch from the board you might try taking it to someone that has an ultrasonic cleaner and cleaning it that way before attempting to open the switch up.
-Lee

 

[nj pheonix]

It may seem like a dumb question
(Like i said before i haven't worked on one)
Is it possible its a standard switch that can be sourced by Mouser (Digikey,.....)?
Also, not looking at it, but if its actually the switch, it seems (from a distance) that an interconnect jumper is a viable (If only, but not necessarily) work around

 

[johnNL]

I have a 919 that had this problem. As I only ever use it as an integrated amp I've had the connection soldered over. As far as I know that's really the only way to stop this switch from acting up -I'v read A LOT of comments from people having the problem you have-. although it's obviously a less than ideal solution if you want the switch's functionality

 

[skippy124]

Re the failure of rca jumper leads to solve the intermittent switch, the design of the switch/circuit implementation is such that there are always switch contacts in circuit irrespective of the position of the switch. This is certainly the case for the 517/519/717 and I would suspect for the 819/919

Cheers

John

 

[Hyperion]

As far as I know that's really the only way to stop this switch from acting up

Well, that's not really true, I did have trouble with my AU-717 and AU-919 until I realised that the only way to resolve it permanently was to dismantle the switch and clean it when it's in bits. However, this is not for the faint-hearted - the switch is unobtanium, so if you mess it up you will have to hard wire it. The 'dismantle and clean' approach worked for both of mine - I recently turned on my AU-717 after around two years of not being used and it worked perfectly.

 

[ghamilton]

This should help...
http://audiokarma.org/forums/index....ated-switch-replacement.111609/#post-10279261

 

[Hyperion]

the switch is unobtanium,

Or so I thought until ghamilton posted above.

 

[jwc2012]

Thanks for the replies and advice everybody. The solutions proposed by ghamilton are exactly what I was thinking about. With those as backups, I can try my hand at disassembling that accursed switch and have alternatives if it goes badly.

Hyperion: Any tips on removing and taking apart the coupling switch? I’ve read EW uses Brasso to clean the parts. What did you use?

ghamilton: A few follow up questions for you. Have you tried replacing the stock switch with the one from Digikey? If so, how did you secure it? Regarding the interior jumpers, do they permanently connect the pre and power amps in direct DC coupling, or in capacitor coupling? My understanding is that the direct coupled connection puts speakers at risk if there is a short or other serious surge.

 

[jwc2012]

That certainly fits with my experience with both amps. However, external jumpers appear to have worked for some folks. Maybe it depends on how dirty/shot the switch is.

Re the failure of rca jumper leads to solve the intermittent switch, the design of the switch/circuit implementation is such that there are always switch contacts in circuit irrespective of the position of the switch. This is certainly the case for the 517/519/717 and I would suspect for the 819/919

Cheers

John

 

[Hyperion]

Hyperion: Any tips on removing and taking apart the coupling switch? I’ve read EW uses Brasso to clean the parts. What did you use?

For really bad oxidisation I use 'Silver Dip', a watery looking silver cleaner that smells like drains. Applied using a cotton bud, followed by copious amounts of plain water then carefully dried. For less stubborn deposits, or to finish off I use DeoXit or Corrosion X.
Silver Dip
https://www.goddardsshop.co.uk/godd...MIjdvN1MX12QIVqrDtCh1B0Q3iEAQYASABEgIZPPD_BwE

There must be an alternative/similar product available in your area.

 

[ghamilton]

Thanks for the replies and advice everybody. The solutions proposed by ghamilton are exactly what I was thinking about. With those as backups, I can try my hand at disassembling that accursed switch and have alternatives if it goes badly.

Hyperion: Any tips on removing and taking apart the coupling switch? I’ve read EW uses Brasso to clean the parts. What did you use?

ghamilton: A few follow up questions for you. Have you tried replacing the stock switch with the one from Digikey? If so, how did you secure it? Regarding the interior jumpers, do they permanently connect the pre and power amps in direct DC coupling, or in capacitor coupling? My understanding is that the direct coupled connection puts speakers at risk if there is a short or other serious surge.

I never tried the new switch. I suggest that you do it in DC coupled. Unless there is something wrong in the system DC is the way to go.

 

[jwc2012]

I never tried the new switch. I suggest that you do it in DC coupled. Unless there is something wrong in the system DC is the way to go.

But isn't that precisely the key point? If there is something wrong, or something goes wrong, with the amp, don't your speakers get a straight shot of DC that can/will fry them if the amp is set to DC coupled?

I confess, I've never been able to hear a difference between DC and capacitor coupled settings. That could be because the switch and/or other components are deteriorated, or because my hearing isn't good enough. But my hearing is actually pretty good as measured. Does DC coupled really make much difference (at least on a reconditioned Sansui of this vintage)?

 

[jwc2012]

For really bad oxidisation I use 'Silver Dip', a watery looking silver cleaner that smells like drains. Applied using a cotton bud, followed by copious amounts of plain water then carefully dried. For less stubborn deposits, or to finish off I use DeoXit or Corrosion X.
Silver Dip
https://www.goddardsshop.co.uk/godd...MIjdvN1MX12QIVqrDtCh1B0Q3iEAQYASABEgIZPPD_BwE

There must be an alternative/similar product available in your area.

Great. Thanks! And the extra actually can be used to clean our silverware. I'm happy; my wife is happy; all is good.

 

[lbcgav]

I just got done taking apart my preamp/power amp separate switch on my AU-D707 for cleaning. I used some Simichrome polish on the contacts and D5 to prevent future oxidation. It wasn't as bad as I thought it would be, although the whole process did take nearly two hours. I hope that was the only cause of distortion I was getting. So far so good.

 

[Scott Muni]

I removed the board during a complete recap. Disassembled the switch using small cutting pliers to slightly bend the tabs holding it together.
Used q-tips and contact cleaner to remove most of the junk. Then polished using a eraser, nothing abrasive here.
Paper soaked in contact cleaner to clean the sliding contacts.
It was pretty messed up inside.
Then added deoxit before assembly.
With the board removed also recapped the coupling caps.
Removing the board was the most time consuming part, plus the plastic rivets were replaced with new ones from digikey.