Bad Micas? - Videokarma.org TV - Video

***Eric H*** · #1 02-08-2009, 04:15 PM

I've been working on this Tele-Tone Porthole for the last couple months, finally got it recapped and replaced some out of spec resistors.

It plays pretty well but I'm having one last problem and I'm thinking it could be some bad Micas in the Horiz circuit.

It'll play fine for a while then it starts to tear at the left edge, sometimes it flops over completely or tears so bad it's unwatchable.

This is basically a 621/721 chassis, it has three trimmers on the back of the chassis for Horiz Drive, Frequency and Locking Range.

There are Micas connected to the trimmers so I'm suspecting they could be the problem?

Pic 1 is working normally, pic 2 shows the tearing.

M3-SRT8 · #2 02-08-2009, 06:36 PM

I would certainly suspect the Micas. I'm doing a 1948 Philco 48-1001, and there are 7 Micas, thankfully, only seven, to worry about. I tested them all and they were fine, except one.

However, I haven't fired up the Chassis with CRT yet, as I'm waiting on a Focus Pot, and a few odds and ends. If I get the symptoms your reporting, I'll replace what Micas are suspect.

That's all there's left, as I have completely recapped the entire Set, except the Micas.

I'll know Tuesday. If I were You, I'd shotgun the Micas in the affected circuit.

LJB

Phil Nelson · #3 02-09-2009, 10:37 AM

Yes, some old micas are showing their age. I replaced a few in my RCA 630TS on the advice of another restorer.

Phil Nelson

kx250rider · #4 02-09-2009, 11:56 AM

A lot of those "micas" aren't really mica caps at all... Especially the reddish-brown ones in the RCA chasses. They're nothing but paper caps in a flat bakelite casing. I usually find the ones on the horizontal oscillator transformer way out of spec, along with the ones coupling the tuner output to the 1st IF, and the IF interstage coupling caps. Replace with true Mica caps, if you can find them.

Charles

wa2ise · #5 02-09-2009, 12:56 PM

Horizontal circuits work their caps a lot harder than RF and IF circuits do. So the horizontal micas (if in fact they are micas) could be bad.

marty59 · #6 02-09-2009, 01:37 PM

I agree with the posts but for troubleshooting purposes, take a little freeze spray to the suspects one at a time and see what happens.

M3-SRT8 · #7 02-09-2009, 01:39 PM

Those epoxy dipped micas are still available, 500 volt rated.

LJB

***Eric H*** · #8 02-09-2009, 09:22 PM

Can these be replaced with Ceramic Discs? Those I can get locally otherwise I'll have to order them and wait.

At least a couple of them are rated at 1000v by the way.

radotvguy · #9 02-10-2009, 12:42 PM

I had to order a few replacements for mica caps, got them from Moyers . Silver mica caps i think they were @ 600 v . Worked just fine in the Philco i finished and they were in the horizontal deflection circuit .

***Eric H*** · #10 02-10-2009, 12:47 PM

I think I'll just make up a list tonight and order the Micas, there are only a half dozen or so.

They are all in the Pico range, 5-500 Pf I think.

BTW, this seems to be a Phasing problem rather than Frequency, the picture doesn't flop sideways so much but mostly just shifts sideways so the picture's split in the middle.

jeyurkon · #11 02-10-2009, 03:24 PM

Quote:

Originally Posted by Eric H

I think I'll just make up a list tonight and order the Micas, there are only a half dozen or so.

They are all in the Pico range, 5-500 Pf I think.

BTW, this seems to be a Phasing problem rather than Frequency, the picture doesn't flop sideways so much but mostly just shifts sideways so the picture's split in the middle.

Now I'm waffling. In the range of 5-270pf you could get COG disc ceramics that are very stable and have low dissipation. It would be hard to find values above that though in COG. You're probably better off getting the micas, but now I'm curious.

John

M3-SRT8 · #12 02-10-2009, 07:22 PM

In the Philco 48-1001 I'm working on, I just replaced all the "Domino" micas with Epoxy-dipped 500v micas. They all tested fine at rest, but, to quote Remo Gagji in "Casino:"

"...Why take a chance? Anyways...that's how I see it..."

LJB

PS: These "Domino" Micas are 60 years old. Plus, they control some pretty picture quality-related circuits. Time for Retirement...

***Eric H*** · #13 02-10-2009, 10:41 PM

I could get a few discs and see what happens, they're well under a buck each locally.

The set won't sync at all now, it's pretty much stuck with the bar down the center, that might make it a little easier to fix!
It was acting up only now and then which is a major PITA to find.

I'd like to get this thing off the bench (i.e. kitchen table) so I can start on the monster Philco 49-1280

***Eric H*** · #14 02-12-2009, 05:07 PM

I spent a couple hours on this last night, up till 3:00am actually and went to bed frustrated.

The set worked good after the initial recap but would tear and pull sideways occasionally, the last couple days it crapped out completely and the picture was a jittery mess.

I found a 100pf cap on the sync sep tube that responded to heat, I replaced it with a .001 mylar, it worked and the picture was rock solid but now it was split down the middle with two pictures side by side.

I fiddled for two hours replacing resistors and subbing caps to no avail.

This morning I turned it on again and it works perfectly, go figure.

I still think it has some bad Micas or whatever these square flat caps are, they are Micamolds so who knows but I'm going to replace them (one at a time of course so I don't get myself into more trouble)

jeyurkon · #15 02-12-2009, 09:18 PM

Pretty nice picture when it's working! There's a lot of detail in that tree.

John