Sounds like some how you now have noise being introduced most likely through the AC circuit. Hum typically is carried through the ground, which is the third wire.
I imagine a defect in a LST-4200A could possible cause AC hum to be bled into the audio or video outputs.
Let us know what the outcome.
-Robert
I imagine a defect in a LST-4200A could possible cause AC hum to be bled into the audio or video outputs.
Let us know what the outcome.
-Robert