[R-390] R-390A BFO

[wabate]

Hi,

Just finished the cosmetic restoration of another 390A.  Its looking 
pretty good.  Turned it on and was able to hear some stations without 
doing an electrical alignment.  I started to check the various functions 
when I found the BFO was not working right.  I could go from zero beat 
to a 3 KC pitch on the minus side but on the + side it would only go to 
about 1 KC.  I took the shaft off and spun the BFO shaft with my fingers 
and every revolution it would go low and then high repetitively.

Finally figured out this had to be an inductance problem.  So I took the 
BFO apart.  Never saw the insides before.  Sure enough, it appears that 
the slug (or something) is against the pivot point at the end of the 
coil form and it wont retract.  If I turn the shaft counterclockwise I 
can see the bakelite disc support flex as the slug tries to move out. 
So I'm against the stop. When I turn the shaft clockwise, it just 
unscrews. So the slug is jammed or something.

Are there any articles on BFO repair?  I don't remember any.  Anyone 
been down this road? I can't be the first.  Its difficult to understand 
what is going on mechanically as there are threads inside of threads. 
One is left hand and the other is right.  I don't want to destroy 
anything in my learning process if I can avoid it.  THis BFO was 
serviced by someone before as there are pliers marks on the outside 
collar. So someone has messed with this.  There may even be parts 
missing! AARRGGHHHH!!!!

Thanks,

Bill, K3PGB