[R-390] Help! R-390 Meltdown

[Tim Shoppa]

Rick writes:
> Since I saw where the smoke was coming from it was easy to spot the failed
> component - it was R 220 which I've traced to part of the 3rd IF circuit.

You're talking about the 2.2K resistor in the 3rd mixer?

In both the 390 and 390A there's a lot of 2.2K resistors that smoke/char when
there is excessive plate current. Even though they're often out of spec, they
aren't usually the cause of the excessive plate current but rather a symptom.

Look at V205 (the 6C4 mixer) and its grid bias circuit - supposed to be a 1Meg
to ground. With the 6C4 out of the socket you should measure 0VDC at pin 6
of the socket, and you shouldn't be smoking R220 anymore. If the 6C4
is out and you are still smoking R220, maybe a short in the T207 can.

Tim.