Leaving JCM 800 on in Standby mode.

[dommarsh]

That sounds like a problem with the switch. Contact corrosion can cause increased resistance and heating. Maybe replace it, sounds like a fire hazard.

Sounds like a defective switch. If the switch doesn't make good contact when on (closed switch), there is resistance across it. With current going thru it to feed the circuit, you have power dissipation at the contact. (Current squared multiplied by resistance gives you power dissipation)