problem in my deluxe big muff / EH1330A

[taku0319]

Hello Gurus,

Today I got vintage deluxe big muff.

It works big muff side and soul preacher side but big muff side has little problem.

That sound comes with like a half fixed wah tone.
Please confirm with below youtube.

https://youtu.be/xpgazYTDSa4

If anyone can advice suspicious point, really appreciate.
Schematic is attached.

Takuto