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PostPosted: January 30th, 2020, 12:36 pm 
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Anyone out there that has vintage audio equipment can utilize this method on open-frame switches whether the switch components are silver or bare copper and/or brass. Abrasives can work with limitations, but not recommended. You do not want to damage the fit-and-finish of a viable switch.

My McIntosh MR-67 FM tuner developed a problem where the left channel became much lower in level and distorted. To make a long story short -- it turned out to be a corroded mode switch (heavy silver oxide) that passed both the mono output to the audio output stages from the ratio detector (one switch position) or stereo output (second switch position) from the multiplex board. To add insult to injury -- the switch was no longer available -- no vendor had any of these 50-year-old switches sitting on a shelf looking for a home.

As it turns out the switch looked worse than it appeared, but a solvent-based contact cleaner could not get the job done. Hell – it barely mattered. So – if that didn’t work – what will? :confusion-confused:

TarnX (an aggressive liquid silver-cleaner) from my well-equipped kitchen together with a moderately stiff utility brush stripped the corrosion (silver oxide) down to some beautiful virgin silver. I used the contact cleaner to flush away the TarnX as remaining TarnX residue will enable corrosion to occur again – then I treated the switch with CAIG DeoxIT to prevent oxidation.

It is important to note that the chassis area near the work site should be layered with some paper toweling to soak up the TarnX during that phase of the cleaning. I kept the paper towel in place even during the contact cleaner flushing. Compressed air keeps things neat and tidy.

I didn't think to photograph the switch before cleaning -- but you can see from the attached photo the restored switch is as good as new. :handgestures-thumbupleft:

I hope this helps.


Attachments:
MR67 Mode Switch.JPG
MR67 Mode Switch.JPG [ 340.12 KiB | Viewed 247 times ]

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PostPosted: January 30th, 2020, 3:24 pm 
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Great job Walt!


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PostPosted: January 30th, 2020, 3:56 pm 
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Walt, et. al.,

I have successfully used Goddard's Silver Dip to clean contacts on silver plated terminal strips, tube sockets and wire prior soldering. It is an essential item to have around. Have not tried the same for cleaning in situ, since it need to have a water wash afterwards. As you well know, rosin flux is just about useless for silver or silver plated components and wire if trying to solder them, even the Cardas solder cannot clean it.

David


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PostPosted: January 30th, 2020, 4:21 pm 
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tomp wrote:
Great job Walt!


Thanks! You should have been here when I was fighting with the pressed-in "rivet like" RCA connector. You probably could not have tolerated the language that flowed from my mouth. :o

It was steel with a ceramic insulator -- the center pin was tinned copper.

You just do not yank it out like a bad tooth.


Attachments:
Fixed Output RCA.JPG
Fixed Output RCA.JPG [ 246.73 KiB | Viewed 223 times ]

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PostPosted: January 30th, 2020, 4:23 pm 
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David McGown wrote:
Walt, et. al.,

I have successfully used Goddard's Silver Dip to clean contacts on silver plated terminal strips, tube sockets and wire prior soldering. It is an essential item to have around. Have not tried the same for cleaning in situ, since it need to have a water wash afterwards. As you well know, rosin flux is just about useless for silver or silver plated components and wire if trying to solder them, even the Cardas solder cannot clean it.

David


In lieu of a water wash I used the contact cleaner and compressed air. I really did not want to use water since the switch was in place when I cleaned it. The contact cleaner got that part of the job done efficiently.

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PostPosted: January 30th, 2020, 4:47 pm 
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I have an MR-67 that I haven't used in many years, partly because of my frustration with uneven output in stereo. I'm going to see if this is the problem - thank you!
Pete


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PostPosted: January 30th, 2020, 5:05 pm 
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SoundMods wrote:
tomp wrote:
Great job Walt!


Thanks! You should have been here when I was fighting with the pressed-in "rivet like" RCA connector. You probably could not have tolerated the language that flowed from my mouth. :o

It was steel with a ceramic insulator -- the center pin was tinned copper.

You just do not yank it out like a bad tooth.


a quarter stick of 40% should do nicely. :crazy:


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PostPosted: January 30th, 2020, 6:58 pm 
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tomp wrote:
SoundMods wrote:
tomp wrote:
Great job Walt!


Thanks! You should have been here when I was fighting with the pressed-in "rivet like" RCA connector. You probably could not have tolerated the language that flowed from my mouth. :o

It was steel with a ceramic insulator -- the center pin was tinned copper.

You just do not yank it out like a bad tooth.


a quarter stick of 40% should do nicely. :crazy:


There is no doubt. Hmmm. Maybe a little piece of C4. :twisted:

The hard part was avoiding chassis damage. The other pair of RCAs are for a volume-controlled output that I'll never use.

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