Sherlock Holmes & the R-390 Applies pretty much to ceramic trimmers in general, I expect. (This is the redacted and short version) Three R-390s fell out of the sky. None were in working condition. After quite a bit of effort the #1 unit was demoused and made to work. Then the plan was to determine the condition of 2 & 3. By swapping known good modules out of #1, both 2 & 3 were made to play. Since the RF deck on #3 was very clean, but the front panel looked like graham crackers in milk (severe aluminum corrosion) the plan was to swap a fresh front panel... but. The "but" was that the chassis on the 390 does NOT have removable side panels, it's all one unit. That left making #2 "the" unit. The side panel on one side had corrosion too. Unit #2 was fired up. All good. Except. Deaf on 4mc, 5, 6 and 7. Found the burnt up 1st can, the ANT tuning can. Pix were put up earlier. That should fix it! Nope. Cans 2 and 3 peak, but the can to the rear does not peak at all. It's one of two between 1st RF amp and 2nd RF amp, actually the 2nd. Sherlock said, swap a can from the other deck! Swapped the can...still didn't work! what's the probability of the same can from a different deck, made by a different manufacturer in a different year not working!! Just about nil. So, obviously there's a flaw in that RF deck that had been transmitted into enough to char that RF input coil. After all the scope and DVM checks I could figure out, the plan was to swap the RF decks. A warm 50 degree winter day meant that i could degrease the gummed up #3 gear train and swap it into #2. After swapping it in, which went rather well, plugging in the cans, turning it on... ahhh! Nah. It still didn't work, deaf on the same bands. Believe me, everything was checked. Last resort - took ALL the cans out of that row from the #1 unit, removed all the cans in the row from #2, and tried it again. SUCESS! But... huh? Really? So that meant, bad cans from two different RF decks!! Later, after a whole lot of swapping of cans, testing, and the like - did I mention that I replaced the two silver micas in one of the cans? Still didn't work! What did that leave? Yep, the TRIMMER! I was able to dissassemble the trimmer and found that the silver had spread across the two ceramic surfaces. Contact cleaner took most of it off. I've tried an cleaned two cans. One returned to proper operation. The other had been lubed with PTFE spray lube, and did not. I may clean it again and retry.