Please help identify potentiometer type

[john3]

This picture is of the wafer out of a 200k dual-gang volume pot. It was the volume pot in my stereo amp, but was getting scratchy. I repaired it, but when I put it back together I squeezed too hard and messed it up again. Then when I tried to open it again, I broke the wafer. Cost me hours, anyway...



There are 7(!) leads, not the typical 6 for a dual-gang. There are two wipers, one that connects the outer copper trace and outer resistive band, and another that connects the inner trace and resistive band. Clockwise from lower-right, the fifth pin somehow combines both resistive bands(?!). I don't understand how this pot is intended to function and what I can use to replace it.

Has anyone seen this before? Thanks for any help.

 

[davenn]

it may have been designed specifically for that amplifier. ie. an inhouse special
most likely going to the manufacturer or service agent will be your only choice.

Try and get a service manual for the unit off the net so you can at least quote a part number

Dave

 

[john3]

OK, thanks, that makes sense. I thought that any pot would be replaceable, but apparently not, then. The volume control is part of a module that connects to the rest of the board with about 2x8 leads; seems complicated. The amp is a 15-20 years old Panasonic unit, at best mid-range, so I'm doubtful that it will be available. Maybe I can find the identical unit somewhere and scavenge the part.

 

[BradtheRad]

The typical stereo volume control used to be two pots ganged together.

Yours has everything condensed into one housing. I've never seen this type.

The common pin is probably ground. I don't know what the 7th pin is for.

If it were me I'd see if I could scavenge a ganged-pair pot from an old stereo. It would take some work to jumper it to the right points on the circuitry, etc.

However it may be no easier to find a ganged pot.

Nor have I seen an easy way to attach one pot to another so that rotating one shaft rotates both.

It might work to apply a bias current to 2 transistors from one pot.

Or run each channel through a CdS light sensitive resistor, and shine one LED on both. Change LED brightness to adjust volume.

Also it seems to me I've heard of an IC which can control volume of two signals with one pot.

 

[krp]

The extra connection(s) is/are probably a "loudness tap"; there is a good explanation here;

https://www.extron.com/company/article.aspx?id=loudnesscontrol_ts