Sth wrong with my crunch box, help plz

[Thugpoet]

I could hear clean sound with the gain pot off.But when I turned the gain a little bit it just 'buzz buzz' and then it became soundless.
The power led always lighting whenever I could hear the sound from my amp.
I checked the gain circuit, it just a 100p cap between the pot.
Should I change a cap or pot? or I have to do other work?

[petemoore]

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