[jeyurkon]

I found an FM-254 and ordered it, but decided to repair the original IF instead. The FM-254 would have been too difficult to use because of the pin-out.

In the first photo you can see the problem with the mica capacitor. Although it looks like silver migration might have been the problem, it was actually a break in the silver on the bottom half that you see. It appears that the mica was bent when installed. It was actually tuned to work with it open. Then it would eventually make contact as it warmed up and detune.

I measured the capacitance on the good side at 23pF. Just for the fun of it I measured the thickness of the mica which was 0.045mm, the area that forms the capacitor as 3.5mm x 5.5 mm and calculated the capacitance assuming a relative dielectric constant of 6 for mica. I came up with 22.7pF.

I installed two 22pF silver mica capacitors internally. You can see the result in the right hand photo. I think most people install them outside during the repair, but there was room and I was confident of the value that I needed.

The FM works great again and is now stable. It only took a minor touch-up on the alignment on the side that was good, on the other side I had to back the slug out many turns. I think the IF had been this way since it was made.

I'm glad that this set didn't have any serious problems to solve since it was my first restoration. Even the minor problems I had to deal with might have stumped me if not for the wealth of information that many of you have made available on your web sites.

John