[R-390] R-390a modified IF sub-chassis

[Larry H]

Gary,  Glad you are still working on this.
With the bfo on, check the plate and screen voltage.  If ok, check for rf output on plate and af on audio filter out with a scope.  If ok, check for audio at input to limiter and check the limiter input bias to cathodes (if switched on) with a vtvm (it must be at least -2 volts).  In a non modified rx, the diode load provides the bias and will go up to -25 volts on high output signals, with the normal of 10-15.  With the NL off, you don't need to worry about the cathode bias.  It will be + (because of the high plate voltage) when the NL is switched off.
Regards, Larry