Is this Presence control solder incorrectly?

[Exodus5]

https://www.flickr.com/gp/26666571@N03/f5CkZ5

The top is the red channel and the bottom is the orange. First off, the pot ohm specs were reversed (red was 100k, orange was 25k) but even after buying replacement parts from Mesa my Orange channel presence doesn’t seem to have any effect on the sound. Red channel, which is the wrong rating, at least works. I also had to set the Orange treble back to stock. Someone changed it from 250k to 1 Meg.

 

[AaronR]

While I don't have a 2ch recto, I am an engineer and also had a look at the schematics.

The orange Channel is wired incorrectly for sure, as the left lug and the middle lug are jumpered. Imagine a potentiometer as a fixed resistor. The outer lugs connect to the ends of the resistor while the one in the middle connects to the wiper which can be placed anywhere along the resistor to divide it into two smaller resistors that add up to the original value.

In the schematic, both presence pots are drawn as variable resistors which means that the wires should be connected to one outer lug and the middle lug. The way the orange presence is wired the pot is always on full, as the entire resistance across the outer lugs is in the circuit.

So remove the connection between the left and middle lug and connect the red wire to the middle one.

I also don't know what the silver wires are supposed to be but I'm sure someone tried another mod there.

Please tell me if that fixes the problem