It looks as though problems with the TMB channel are causing performance problems with the Normal channel. Here is what I have observed when I plug my guitar into the Normal channel (there is NOTHING plugged into the TMB channel):
 
1. The MV (control right above the input jack for the TMB channel) determines the volume of the Normal channel. I thought the MV was only supposed to affect the TMB channel.
 
2. Increasing the volume of the TMB channel (not the MV) adds a huge amount of hiss and static to the Normal channel. I have to keep the volume of the TMB channel at zero to avoid any hiss when playing through the Normal channel.
 
3. The tone controls of the TMB channel also appear to be affecting the sound of the Normal channel. I have to keep the treble control at zero to avoid hearing a high pitch hiss. I also have to keep the bass control at zero to avoid hearing a bassy hum. The middle control does not seem to noticeably affect the sound.
 
So, it would appear that the TMB controls (MV, volume, treble, and bass) are somehow affecting the performance of the Normal channel.
 
 
When I plug my guitar in the TMB channel (nothing plugged in the Normal channel), all I hear is hiss and static, which gets louder as I increase the volume of the TMB channel. I cannot hear my guitar signal at all. It's as if my guitar were not plugged into the amp. When the volume is turned to zero, the hiss and static are gone.

Can anyone help me?