Onkyo M504 Transistor Mica Insulators.

[jasoneyes01]

I have an Onkyo M504 I'm working on. I noticed the output devices are mounted to the heatsink without mica insulators. Is this possible that it is not required on this model. I just received this not functional M504 and need some conformation before I fire it up. This unit appears to have been tampered with as it had a cracked circuit board when I received it.

 

[nigelwright7557]

It depends if the transistors are isolated tabs or not.

 

[jasoneyes01]

As I was cleaning the heatsink, surprising there was a sliver of mica. It was delaminated. Definately need to change these out. My bad. Checking the resistance between the to3p case and heatsink revealed leakage thru the mica on some of the output devices.