The nuts on my PM1000 channel have stripped the pot - what can I do?

[abeLovesDIY]

Hello,

I'm using a 7/16 socket wrench to remove the nuts and washers from some PM1000 channels for racking, going as gently as I can. Mostly so far so good.
For this channel, however, three of the nuts have stripped the pot - meaning the nuts will turn, but not back off.
I'd love for there to be a solution that doesn't involve replacing the pots (since these have four pins and are odd - among other reasons).
Is there a solution that doesn't involve replacing the pots?

 

[JohnRoberts]

I don't think I've ever seen that or anything like that.

Are you saying the nuts destroyed the threads on the pot bushing, i.e. they were harder metal?

Can you get a nut to come off by turning it while prying it away from the faceplate from behind?

Good luck

JR

 

[Script]

This schematic ?



What's the fourth pin on the pots? Pot casing to ground / chassis ? (Bottom right line goes to ground).
No, it's indeed a fixed center tap. Used on PM170 also, but shorter shaft.

Is the rotary held by the same type of nut ? 8/

 

[Brian Roth]

IIRC, those pots have a tap on the resistive element at mid position to ensure flat frequency response.

Bri

 

[Tubetec]

What you can try is adding a couple of extra washers onto the shaft , now the nut sits a bit higher ,you might be able to get the threads to bite . It might be worth adding a tiny amount of threadlock instead of over tightening and stripping it further , be carefull not to get threadlock on the bushing or the shaft could end up seized . Using a socket set/ ratchet handle its very easy to over torque and strip the light alloy threads , a screw driver type handle with the appropriate socket is best , and only go hand tight .

 

[JohnRoberts]

IIRC, those pots have a tap on the resistive element at mid position to ensure flat frequency response.

Bri

Center tapped EQ pots ground that extra center tap to insure flat response at mid rotation.

The technology of tapped elements in pots was used in some old premium hifi system to provide a loudness contour (bass and treble boost) when volume pots were turned down low. At higher volume the loudness contour diminished for flat response.

These pots are more expensive and not still widely used.

JR

 

[abeLovesDIY]

Can you get a nut to come off by turning it while prying it away from the faceplate from behind?

This worked! IDK if I'll be able to get them back on once raked, but it did help me get them out. Thank you!

 

[TromNek]

This worked! IDK if I'll be able to get them back on once raked, but it did help me get them out. Thank you!

To get it back on try;

Wrap a bunch of teflon tape around the shaft.
Use a new nut and screw it on to cut a new thread in the teflon tape.

It's not super strong, but usually works.

Often I will then put a drop of superglue gel on the nut and chassis. It's easy to get one drop off later if you need to get back at the pot.

 

[cyrano]

As a kid, I used to use alu foil in stead of teflon. Even on small two-stroke motor bike engines.

 

[JohnRoberts]

I would be a little concerned about possible chemical reactions with dissimilar metals, and humidity.

JR

 

[Tubetec]

As I said ,
The point on the bushing where the nut spins is low down , building out the shaft with a couple of extra washers should allow you catch usable threads again , its that simple , do I need to make a diagram ?

 

[scott2000]

do I need to make a diagram ?

This? Back of front panel would work too I guess..

 

[Tubetec]

Putting the washers below the frontpanel would cause missalignment in the height of the pots and dials which might cause things to clash , with the washers on the nut side the height the controls sit at is the same , only the nut sits a little higher .

 

[13engrsapper]

This worked! IDK if I'll be able to get them back on once raked, but it did help me get them out. Thank you!

I have a bare parts channel if you still have issues.

 

[13engrsapper]

This worked! IDK if I'll be able to get them back on once raked, but it did help me get them out. Thank you!

If you still have issues, I have a bare parts channel here.

 

[abeLovesDIY]

One of the EQ pots got bent, so I bought a few Alpine 21530909-A Linear 50k center tapped pots. The only issue is that they are very fat and came with no nuts. I looks like my calipers measure the width of the threaded area is 7.7-7.8mm in Diameter. Can anyone provide a clue as to what nut I should seek for this potentiometer?

 

[chilidawg]

One of the EQ pots got bent, so I bought a few Alpine 21530909-A Linear 50k center tapped pots. The only issue is that they are very fat and came with no nuts. I looks like my calipers measure the width of the threaded area is 7.7-7.8mm in Diameter. Can anyone provide a clue as to what nut I should seek for this potentiometer?

Maybe M7 x 0.75
Try salvaging one from a cheap Alpha 16mm pot and see if that'll work.