Stage HT 60 Low Clean Volume

[bglawson42]

Hello, I have a Blackstar HT 60 Amplifier that I purchase 4 years ago from Guitar Center. It has developed a problem with the clean channel. It shows the following symptoms. The clean channel volume is very low about 1/4 of the volume it originally had.. Channel 2 and channel 3 are not affected by this, both channel 2 and 3 are as loud as ever. Its only the clean channel that seems to be affected.

The amp has been at a very reputable local repair shop for over a month now. We have replaced all tubes pre amp and power. He has also ran through all the testing he says he can do on the board, and can find nothing wrong with it. I am looking for some guidance.

Thanks.