In the first instance the power cable from the DC power supply in the lid was bad and when the lid was closed tight the cable would bend and reduce the dc volts to the amp mod thus affecting the levels.
The second instance was actually when I tightened the motherboard down in a Magnavox trunk amp and the solder connection on the seizure screw was broken. When the mod was tightened all the way it applied enough pressure on the seizure screw assemble to affected the connection enough to cause a suck out of some channels.
The third was actually nothing to do with the amp as much as it was to do with me working on it. I had the input power cable ring cracked at the connector so when I applied pressure to the cable it would break ground effecting the AC voltage levels,
