Trimmer identification / calibration

[yekuku]

Hi guys, I would appreciate a little help with this one.
I am restoring an TC 2240 Parametric EQ and there is a trimmer at the input with an undocumented function.
Here are the schematics:

Does anybody understand its function ?
Any ideas on how to adjust it ?
many thanks

 

[ej25awd]

Looks like the non-inverting gain adjustment when operating in unbalanced mode. How is the unbalanced jack terminated? I'm guessing the inverting input gets connected to ground. If you haven't replaced the feedback components of the first opamp, just leave the trimmer alone.