[R-390] Mechanical Filter Repair

[ToddRoberts2001 at aol.com]

Dennis, some people have opened up the R-390A mechanical filters and repaired 
them. The usual failure mode is one of the fine wires from the transducer 
coils to the terminal pins breaks causing an open circuit. This can be repaired 
without too much trouble unless the wire breaks somewhere inside the turns of 
the transducer coil, then it would be almost impossible to fix. Checking across 
the terminal pins with a DVM can determine if the input-output coils are 
open-circuit confirming a break in the wire somewhere. If both input-output side 
terminals have continuity then the trouble could be in the disc assembly 
somewhere and would be very unlikely to fix. The filters have been known to suffer 
from corrosion inside which can cause the fine wire to break. The corrosion 
seems to come from foam-rubber packing that disintegrates over time inside the 
sealed filter cans. Also I think corrosion can occur over time where the fine 
wires are soldered to the terminal pins. Good luck 73 Todd Roberts WD4NGG.