ctc12 clone beam current

[Username1]

Hi Timmy, See posting #291, That capacitor C729, take one leg out of the circuit, or remove
it completely and turn the set on and see what the voltage is on the grid of 12BY7A, if
it's still around 20V then the problem is in another part.... Check that first please...

I don't have a Sams for this tv, just the ctc-12 schematic off the internet, so you
have to use the images I put up to see what parts I'm talking about..... And I can
only follow you if you refer back to those part items the same way....
Also you have to understand tube function.... -7V on G1 turns off the tube.
Anything above that begins to turn it on.... +20V It's ON really ON, so it is to
be expected that the plate voltage will be low because the tube is conducting.....
The only other thing I can see checking is R720, a 220 Ohm resistor in the cathode
of 12BY7A. to be sure it's not open....

On resistors in parallel, There is a formula to figure out exact value, but as a
general rule:

30 ohms || 4,000 ohms you will read close to 29 ohms
10 ohms || 20,000 ohms you will read close to 10 ohms.
200 ohms || 200 ohms you will read close to 100 ohms...

Coils, for the most part are going to be low ohms, 30 ohms or less....
a lot of times they are going to be less than 10 ohms....

A lot of times you can check some items in circuit, but it takes time to learn
what you can, and can't and what to expect. Capacitors block DC and pass
an AC signal, they charge and discharge. In the case of this problem, I am
looking for a reason for the grid to be close to 20V, I can see a path to
a 20V source IF that one capacitor is shorted.... So it is wise to check it and
get that possibility out of the way....


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[timmy]

ok i have in this circuit a .1 but the rca shows a 0.1 so ill lift one leg and see what happens. then ill look into that 220 ohm resistor off pin 1 .

[timmy]

in circuit the 220ohm resistor measures 216 ohms and lifting one leg of the .1 cap made no difference. dont forget i have the chassis out not plugged up to the yoke. there are 2 disc caps 390mmf in between that resistor , dont know if this may be of any concern. it is a royal pain in the !##$@#$$ ass but if i have to left legs out all over to find this problem well then i have too.

[Username1]

Ok, coming off pin 2 R759 do you have 20V on both sides of that resistor...?
What voltage is on center pin of brightness control..?
What is on R733, either side...?

You are running the set with what no HV...?

No one is asking you to lift every cap, just ones that may lead to an answer...
Sorry you are the one stuck doing it all.....

Found cool little website while looking up 12by7a to be sure pin numbers are
right.... Pretty neat..... http://www.intio.or.jp/jf10zl/index.html


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[timmy]

r733 is the 2.2k 38v one side and 25.5 other. no hv hot out. r759 close to the same. bright max 30.32 volts low 23.04 volts. i have a funny feeling this excess voltage is coming from somewhere else further down the pike .

[Username1]

Not quite what I expected.......

Can you check the AGC pot, 6K 2W.... Be sure it's good....

And can you check the voltages around the sync sep. tube....

Images included....

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[timmy]

6ka8 pin 1 86.7 v pin 2 24.65 v 3 25.42 its high even by the sams i have here. agc pot 2601 ohms end to end wiper 6.18 varys.

[Username1]

Ok Timmy I got a funky project for ya-
I need you to find ground points on the PC boards where both of these tubes are, and
do 2 things.... With the tv turned on, measure voltage from the PC board ground to the
metal chassis ground, and see if the grounds on the PC boards where these two tubes
are have and voltage on them..... Second, that AGC pot, 2.6K is not the 6K my schematic
says it should be.... You may need to see what's going on there.....

For the 6KA8, cathode ground should be directly through the AGC pot...

For the 12BY7A, C750 - one side goes to ground... Now you have to use a part,
not the metal lugs that the circuit board is attached to, these are clearly grounded,
but just in case there is a trace broken, and it's a long loop far away from the
circuit board connections to the metal chassis.....

It's really strange for so many voltages to be off and the set still works - kind-of.
So we gotta look for some sneaky thing.... And high voltages like that,
especially on items that should be going low, kinda make me thing bad ground.....

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[timmy]

the agc on my sams says 6000 2 watt which is this set. the grounds of the 12by7 and the 6ka8 from chassis to the ground of the tubes with tubes in ?

[Username1]

Yah, don't take them out...

The tubes won't have a ground, you gotta find parts on the PC boards that go to
ground on one side, and just check to be sure electrically, they are really grounded.
One way is to check the grounded part, to the metal chassis for any voltage....
It sounds strange....

Take a look at C750, it's one example of a part with one side going to ground.

On that AGC pot, disconnect the two legs that do not go to ground to test it....

AGC pot, pins 1 to 3 should be 6K thats 6,000 ohms.... The wiper will
change as you turn it you know, from the wiper to either pin 1 or 3....

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[timmy]

on mine 2 legs tied together go to ground and has one wire on one tap.

[Username1]

yes I have it too.... Just be sure it maxes out at 6K, and trims down all the way to zero... as it is in the circuit....

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[Username1]

Ok, more goofy stuff for ya-

Please check the voltage at pin 7 of 6BZ6 V301. Schematic says it should be
around 35V.

Please check the voltages on both sides of R307...

Please check the voltages on both sides of R312, and pins 7 (165V)
and 2 (0V) of 6EJ7 V303....

Is that AGC pot mounted on the PC board or is it mounted on the metal chassis....?

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[timmy]

ok pin 7 of 6bz6 38.7 v both sides r307 38.2v and 0 v r312 4.17 and 0 v 6ej7 pin 7 155v pin 2 0v

[Username1]

Originally Posted by timmy

ok pin 7 of 6bz6 38.7 v both sides r307 38.2v and 0 v r312 4.17 and 0 v 6ej7 pin 7 155v pin 2 0v

Gotya - Are you sure - absolutely sure R 307 1500 ohms 1 Watt resistor has
38V on both sides of it.......?

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