IF Transformers

Silver Mica capacitor Disease The crashing thunderous roar in the AM band.

After hours of burn-in this radio (Blaupunkt Sultan model 2320) developed static. It started as an occasional pop. Like the sound you get when some one turns an appliance on or off. It just progressively worsened. And the eye tube seemed to be fluctuating with the AM modulation. So I embarked on the delicate task of disassembling the IF cans, removing the internal mica wafers and adding external silver mica 600 volt caps. Join me below.

Archive pic of 1st IF wires.	The radio plays great. BUT there is the thunder storm sound. Silver Mica disease in the first IF.	I first try to repair the IF on chassis. But I had to remove it for bench repair. I marked one fine wire from each coil and the associated solder lug with red and green Sharpies.	You can see the round insulator that is covering the capacitors.	A mica disk and with parallel silver plates applied. Contacts touch the silver. There are two caps (parallel plates) on this mica insulator. One upper right and one lower left.
I used some fingernail polish to establish the UP side and how it is placed on the contacts.		You can see something black on the upper cap. That is normally silver migration. Electrons break over that migration and cause the rushing sound of a thunder storm. Unaffected by band or frequency.	Measure and record both cap values.	Both caps are the same value. If I can not fix this mica, individual silver mica caps will be soldered on the under side terminals, this mica will be discarded and the cap contacts cut off.
A razor knife scrapes off the back contaminant. I have successfully done this to several IF caps. At this time it looks like the electrolytic can cap has leaked and contaminated this capacitor. There is a moisture looking stain on the chassis surrounding this IF leading to the can cap. It dose not look like silver migration.		Burnish the capacitor contacting surfaces. Do a complete job.	Reassembled IF transformer. See the little bits of insulation on the lead wires (bottom side). I leave a tiny bit so I know what wire came from where.	And that is one fix for Silver Mica disease. Adjust the IF and the radio sounds great. RF alignment later in the week.

Silver Mica capacitor Disease The crashing thunderous roar in the AM band.

Now for a quicker way to remove the mica wafers.

Silver Mica Disease. The thunder storm in the radio. (Zenith T600 Transoceanic)

That is when the EMF (voltage) across two mica capacitors (housed in the IF cans), on a common mica insulator, short together. Removing the two capacitors and soldering on new ones of equivalent value is an easy fix. Here is an alternative.