Trimmer Cap Question

[Chris K]

Hi all. Trying to track down a “twitchy” horizontal frequency signal. The trace isn’t stable and jumps every second or so in frequency going way out of range and then stabilizing. It’s the correct shape…just twitchy. There are mica compression trimmers for horizontal drive and lock in the circuit. I’m wondering if they might be the culprit? This may be a stupid question but do these trimmers get silver mica disease? Can they intermittently short?

[zeno]

Sub them one at a time with close values. Try one, then put the original,
Try the other then back to original.
Sams should have the value range. will be in pf and read like
10 pf - 100 pf choose something mid range.
Odds are there may be retuning but it will prove that out.
BTW I never seen one bad, just piston caps on modern sets.
BTW 2 Make, model, chassis ## ??

73 Zeno
LFOD !

[Chris K]

Admiral 20X1. The values…from memory…I’m not in front of the schematic, 10-130pf and 40-380pf. I got 2 Arco trimmers, 463 and 465 off eBay that are sorta close to that range. I know it’s a shot in the dark but running this down is a pain. It’s not my scope…it happens on all 3 scopes I have including a new digital scope.

[Chris K]

Another valuable lesson learned… I took out every tube and cleaned the pins and sockets with a brass brush and DeOxit 100 in the bottle with the brush applicator. Took about half an hour. The tv works perfectly. All of the instability issues disappeared. Next restoration tube testing and cleaning get done right away!