Rare find! A Magnavox Brittany tv!

[Yamamaya42]

Originally Posted by bandersen

Yes, 100pF rated for 500 volts.

brown - black - black = 100pF

green = 500 volts

then it's VERY bad, and the source of the weak vert lock! and most likely the wonky horz as well, found my first real bad mica! wow!

[Yamamaya42]

So, this wonky mica is C155, the coupling cap between V15b 2nd sync amp and V17b sync clipper, with a leveler in the middle, 120v dc potential across it, with a signal of about 90V P/P being passed.
http://suzaku.live-evil.org/magie-mica.jpg
Seems that the part was so bad, that my digital M-tester could not ID what it was, too leaky i guess, but the LCR tester tested it 160pf, way over spec, I would dare say it had SMD, if these types of caps could even get that, which I don't believe they do.

Which brings me to wondering how I ever got any H or V lock with a cap in there that far off spec, and wonder if there are any others in there which are as bad as that one.
I have not put in the new one yet, but did test it in the M-tester, 98pf and the LCR tester 100pf, I guess it's better calibrated, it DID cost x2 as much!

[bandersen]

160 isn't that far off from 100 and will pass a signal just fine. It's not a tuned or precision circuit so that value isn't critical.

I'd say a coupling cap could easily be +100% or more and you wouldn't notice a difference. Now if it was shorted or very leaky that's another story. IIRC a leaky cap will measure as having a higher capacitance.

[Yamamaya42]

It has to have been very leaky, as the M-tester just could not ID it at all, I have only seen it do that on really bad caps.

https://www.amazon.com/HiLetgo-Multi...d_i=B01MYU0QI3

Not the best thing, but it has it's uses.
It had no problem with the old 82pf cap in the set, but after 10-12 tries, the 100pf kept coming up as unidentified / bad part, so it be too leaky for it.

The LCR meter, does not test ESR, so it does not care, if i had one of those old style cap testers like you have that could push it up to the rated 500v, I have no doubt the light would be blinking like a strobe light!

[Yamamaya42]

new 100pf cap is in.

so is the 330pf.
http://suzaku.live-evil.org/0626251936.jpg
I'm pretty sure that's 300 pf on the old one. edit TYPO 330 :P

http://suzaku.live-evil.org/0626251933.jpg
I think the tiny one is the 5pf but the big one is not on the schematic, no idea what it is it's across the varicap.

http://suzaku.live-evil.org/0626251931.jpg
and I'm sure that;s the 1800pf, hard to see it in there :O

[bandersen]

330pF on the old one.

100pF across the variable cap.

Yes, 1800pF on the big one.

[Yamamaya42]

kinda sux cause I got only 1 100pf so far.

perhaps i won't needed it.

the 82pf was ordered today and is on the way, a disc cap as suggested, npo
75-561R10TCCQ82
there was 1 more ordered for the vert section 4700pf that i could not get in npo, the best i could get was X7R .
594-H472K47X7RL63J7R
a Mica one was $12-$ 15

[Yamamaya42]

Was able to confirm that the 100pf cap is indeed leaky, took it to work, hooked it to the bench power source, turned up as high as it would go, 37v, + into one end and – on the other via a 1m pull down, and the DVM saw about 25v leaking through it. Repeated this with the 330pf cap and it was 0v.

It will be interesting to see what I get when I try this on the other mica caps I remove from the set, I just wish I had a source that went a bit higher like 200-300v to really push these caps.
But to be leaking at less than 50v is pretty bad!

[Chris K]

Originally Posted by Yamamaya42

new 100pf cap is in.

so is the 330pf.
http://suzaku.live-evil.org/0626251936.jpg
I'm pretty sure that's 300 pf on the old one. edit TYPO 330 :P

http://suzaku.live-evil.org/0626251933.jpg
I think the tiny one is the 5pf but the big one is not on the schematic, no idea what it is it's across the varicap.

http://suzaku.live-evil.org/0626251931.jpg
and I'm sure that;s the 1800pf, hard to see it in there :O

Hey...they look like my favorite Chinesium resistors!!!

[bandersen]

Originally Posted by Yamamaya42

kinda sux cause I got only 1 100pf so far.

perhaps i won't needed it.

the 82pf was ordered today and is on the way, a disc cap as suggested, npo
75-561R10TCCQ82
there was 1 more ordered for the vert section 4700pf that i could not get in npo, the best i could get was X7R .
594-H472K47X7RL63J7R
a Mica one was $12-$ 15

You'd probably be better off using a plastic film cap than an X7R ceramic. Is the existing 4700 bad?

BTW you can get a 4700pF mica from JustRadios for $5. https://www.justradios.com/cart.html
I too use Mouser for most stuff but when it comes to more specialized caps (like 6,000 axial film caps), JustRadios is often better.

[Yamamaya42]

Not sure that it is at this point, if you look at the schematic, it's C160, sitting right on the yellow wire of the vertical block oscillator transformer, leading to the vert hold pot wiper via a 1m pot.

I am looking in the area cause there was very touchy / weak v-lock / sync, but this all could have been a symptom of the bad 100pf cap in the stage before, (sync leveler) could it not?

[Yamamaya42]

OK, after all the new parts, it still works!
vertical lock /hold is much more stable!

horizontal is still a bit touchy, having to tune in the varicap (h-lock) all the way, to get it stable, had to order yet another 100pf cap from mouser, spending more on shipping than the part, as I only had one.
sure, I could have gotten it cheaper from someplace else, but they take 3-5 days, and mouser gets it here in 1 day, no matter what!

[bandersen]

I suggested Just Radios because you said the 4700pF mica from Mouser was too expensive.

[Yamamaya42]

Originally Posted by bandersen

I suggested Just Radios because you said the 4700pF mica from Mouser was too expensive.

Correct, the original 4700pf is still in there, if the v- lock was not better after replacing these parts, then i would have looked into replacing it.
A few other places had the 100pf cap cheaper, but has a 3-5 day shipping window, I picked Mouser as they are 4-5 hours from here, so no matter how they ship, it's always next day.

Basically, I'm getting a bit excited now,SO CLOSE NOW, so close to slapping the 16LP4A in the set and seeing if it all works right, IE, the ion trap, focus coil circuits. If things hold up well with the test CRT as they seem they are, it looks like the chassis is pretty much done.
Thus I'm being a little foolish and and not willing to wait for parts from someplace a bit farther away!
Mouser is just down the street, in a "Texas" sense!

[Electronic M]

I most cases where a 1000pF or higher Mica is used you can get away with a standard film capacitor... which is what I usually do.