[R-390] R390A BFO /100kc calibrator not working

[Roger Ruszkowski]

Chuck,

I so hate oscillators that do not oscillate on request and you have two of them.

The BFO could be on and just so far off frequency you can not hear it.
The circuit will tune completely out of the band pass of the IF filters.

If the AM works then the BFO and VFO tube filaments are OK.
The  tube was checked and tested good.
We expect the BFO to oscillate when the switch is on.
A quick DC volt meter to the plate pin on the tube socket will determine if the BFO is being switched on and off and there is B+ at the tube socket.
Check the DC screen voltage while you are on the socket.

Next level is clean switches wire harness connectors and tube sockets. De Oxit.
Looking for cold solder joints and bad parts.

Have you looked at the IF and RF deck caps yet?
Do you have the big brown or black plastic caps still in the decks?
These are known to go bad as they are over 50 years old already.
The other small caps hold up OK.
The carbon resistors are drifting way off and you may need to replace a few.

The ground points in the decks are solder lugs with small bolts to the chassis.
These are starting to oxidize and cause problems. You just have to loosen each bolt clean the joint up and re tighten the bolt.
I do not explain why this works but it is a reported cure.

Use the same process on the calibration oscillator.
The documentation for the R390A is at R390.net 
There is the nice Y2K manual , TM 11-5820-358 35 the original military TM and a long inspection list available.
 The pearls of wisdom are also there. With whole sections of past experience with the BFO and calibration circuits.

Read all the input you get, lots of Fellows commenting with different good ideas.
Just like it was done in the shop back when.
Fellows, I have a real problem what do you suggest I check next.

Please tell us what you find so your story will make it to the archives.

Roger Ruszkowski AI4NI
Roger