Strange fader behavior-- spot my mistake?

[soapfoot]

Racking up a pair of Auditronics 501 channels (schematic here) and testing a few things on the bench.

The only thing that seems strange is the fader (I chose a 10kA rotary pot).

Using a 1k tone and watching on the scope, I have maximum attenuation somewhere near mid-rotation, and then it seems to start increasing in level again as I approach full-counterclockwise.

Has anyone ever seen anything like that?

I've got it wired as follows:

P2 pin 17 = wiper (output)
P2 pin 18 = lug 1 (ground)
P2 pin 19 = lug 3 (input)

Any help, advice or leads would be greatly appreciated!

 

[ruffrecords]

I find the pin numbers on the schematic very hard to read but I reckon pin 19 is ground and 18 is the top of the fader.

Cheers

Ian

 

[soapfoot]

I find the pin numbers on the schematic very hard to read but I reckon pin 19 is ground and 18 is the top of the fader.

Cheers

Ian

Indeed, quite hard to read.

I swapped those two around and have similar behavior.

 

[soapfoot]

Got this sorted. One of the four ground points wasn't properly and securely connected to the others. I figured it was something simple like that!

 

[ruffrecords]

Excellent. Most faults turn out to be something simple. Subtle faults are (thankfully|) few and far between.

Cheers

Ian