AB763 hum question and fix.

[KimboDb]

Hello again. its been a while since ive posted and was wondering if someone might be able to help. I have a AB763 one channel amp and it works great with one minor problem. It has a hum. the hum dissipates some after a little bit of time most of the time and it can't be heard when playing. Ive read a couple other related post and Ive seen it said that the amp should be dead quiet. Also if i hit the amp a couple times the hum dissipates some. I have pulled the phase inverter and the hum stops completely and also if i throw the standby switch to standby the hum disappears immediately. Thanks ahead of time. ill get some pics up of the board in a little while.