[R-390] R-390A BFO

[Barry]

> 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

If you decide it's not repairable, Fair Radio sells new BFOs.

Barry - N4BUQ