mica capacitors - Page 3 - Videokarma.org TV - Video

bandersen · #31 04-08-2015, 02:31 PM

V12 plate voltage comes all the way down through the resistor divider from the HV output. That's why it's so important that all the megaohm resistors and the HV output be good.

timmy · #32 04-08-2015, 02:41 PM

so if the voltage that should be on pins 2-5 come from the focus circuit it should be there since i changed the resistors at the 6sl7 i think they were 6.8 meg and also all the 4.7 k resistors at the hv pots for horiz and verticle. the voltage behind the 6.8 meg resistors is around 900 volts, is this right or should it be higher. because what feeds the 2 6.8 come from the focus pot and also changed the 2.2 megs, 2, and the 2.7 megs. the hv is under 5kv. i dont know if this helps any but recently the hv oscillator tube suddenly the heater got super bright so i shut it down tried another one it was ok then i tested the one that went bright and it too was ok, i dont know why this would have happened.

Tom Albrecht · #33 04-08-2015, 03:55 PM

V12 (vertical output) gets its plate voltage for both sections (pins 2 and 5) from the focus control, which in turns gets its voltage from a resistor chain fed by the HV.

You correctly note that your voltages on pins 2 and 5 (+140 V and +43 V) are too low, telling us that something is wrong.

There are probably two main ways this can happen:

1. Not enough drive signal from the vertical oscillator. If the signal on the grids of V12 are too small, then both triodes will tend to conduct too much, pulling their plate voltages low.

1a. If the grid drive on just one of the two triodes is too weak, it could still cause this problem. One way this could happen is if there is a problem in the network that feeds the inverted signal to the second triode (grid = pin 4). Can you confirm that C65, R65, R64, C67, C66, and R62 are all correct value and good?

2. Supply voltage to anodes is low. This is fed from the high voltage through the following resistors: R4, R5, R80, R81, R82, R83, R3, R61, R63. Have you confirmed that all of these are OK?

Is your HV correct? Do you have a HV probe to confirm that there is 4-5 kV there? If you don't have a HV probe, let me know and I can suggest how to use a microammeter (if your DVM has this function) to read your HV.

(edit: sorry, didn't see the posts on the new page yet when I wrote this reply -- see below)

Tom Albrecht · #34 04-08-2015, 03:59 PM

Quote:

Originally Posted by timmy

so if the voltage that should be on pins 2-5 come from the focus circuit it should be there since i changed the resistors at the 6sl7 i think they were 6.8 meg and also all the 4.7 k resistors at the hv pots for horiz and verticle. the voltage behind the 6.8 meg resistors is around 900 volts, is this right or should it be higher. because what feeds the 2 6.8 come from the focus pot and also changed the 2.2 megs, 2, and the 2.7 megs. the hv is under 5kv. i dont know if this helps any but recently the hv oscillator tube suddenly the heater got super bright so i shut it down tried another one it was ok then i tested the one that went bright and it too was ok, i dont know why this would have happened.

Around 900 V probably is correct at the junction of R61 and R63 (6.8 M resistors on the plates of the vertical output). Your HV looks like it is fine. You mentioned 4.7 K above, but those should be 4.7 M (just a typo? or wrong value in there now?)

If you've got indication that some filaments are too bright, check the AC voltages on the filaments and see if something is wrong there.

timmy · #35 04-08-2015, 04:28 PM

r61 63 are new and checked again. the 4.7 is meg if i put k my error. i checked the filiment voltage and its good so maybe the tube had an aging moment but tried another and no change. i checked the voltage at the hv oscillator pins 3,4,5 there is almost nothing there. omg... its a mess....

timmy · #36 04-08-2015, 04:35 PM

i checked pins 3-4 should be 225vdc so i used my dvom and its showing me 100v then milli volts so i tried another meter and its showing me 110volts both at those 2 pins and pin 5 should be neg 37 im getting neg 0.47 sorry i didnt say what tube its the hv oscillator v14

timmy · #37 04-08-2015, 05:01 PM

strangely now i just noticed that the image is upside down, turned over and it was not when i had originally put it away until i got the caps. so between the image and the verticle size, didnt have that when i left it to wait for the caps. unreal.... well weather or not the 200, 680, 900 micas will make a difference ill change them when they get here, still waiting.

Tom Albrecht · #38 04-08-2015, 05:02 PM

Looks like your HV is fine, so no need to check the HV oscillator. Right now I'm suspecting scenario 1a in my post above (copied again here):

1a. If the grid drive on just one of the two triodes is too weak, it could still cause this problem. One way this could happen is if there is a problem in the network that feeds the inverted signal to the second triode (grid = pin 4). Can you confirm that C65, R65, R64, C67, C66, and R62 are all correct value and good?

Also check for any possible wiring mistakes in this area (in case you accidentally made a connection wrong on a replaced part. Check against schematic).

Since you're showing such a low voltage on pin 5, I have a hunch that the grid to that triode (pin 4) isn't getting a proper drive signal.

Electronic M · #39 04-08-2015, 05:09 PM

As for the picture being upside down after putting in caps. Were any of those caps the 6KV deflection caps? If so swapping which cap connects to which terminal on the VO tube will reverse the vertical deflection.

timmy · #40 04-08-2015, 05:20 PM

the weird thing here is i originally had a full screen and the verticle did work but only if the hold pot was maxed at one end and gradually it got worse until i laid it up waiting for caps and all of this started after turning it on. when all it was was it seemed that the hold pot was out of range then i had to replace the rest of the disc caps and a few micas. the caps were 1kv disc caps 1kv micas and the others are 1kv also. i had also changed the vert centering thinking this may be harming something but no good maybe i reversed the 2 caps there for the pic to be up side down. ok ill go over a few things here including the caps and resistors you mention as well as go over what i did around the v o tube. i would hate to think that one of the 5, 6kv caps may be bad if this would cause this i dont know. all this started befor i put any of these caps in but i put them in anyway thinking there were a few bad but it never helped.

Gregb · #41 04-08-2015, 05:50 PM

Maybe a good bright clear picture of the underside of the chassis and maybe someone will spot a problem. Sometimes a second set of eyes works wonders.

Gregb

timmy · #42 04-09-2015, 07:35 AM

ok, i messed up and have no idea how i did , it was brainless as i placed the 100mmf lead on pin 5 rather then pin 2. so i have it all back and its working like it did when i first got it done that is with the vert hold pot close to one end but the vert is holding and long as it stays this way and dont get worse then thats ok. but thinking as things wear out i may need alittle more range on the hold pot for the future but then again it wont be an every day tv to watch. the blanker circuit really just gets a 220k resistor between the 250mmf and 10 meg and move #3 orange to in between the 220k and 250mmf, that will be nice if it gets rid of those lines. well with that 100mmf in the wrong place i guess anything can get you unfocused at some point and then there is when the trouble starts and this is what happened to me. i sometimes think by being to careful it can introduce mistakes, at least it seems i am this way with some things,lol. well tom you nailed down where i probably made the mistake and by having a hunch about the signal not getting to where it should be, you were right and i thankyou for your patients because this should tell some people including myself that mistakes can be made and we should not think for a minute that we didnt because i was so sure i made no mistake, but i did. so after i button up a few things with this chassis i will post some pics.

kvflyer · #43 04-09-2015, 09:06 AM

I wish I could say that I had never done that. But, for sure I have! Then, when I look back, I think, "How could I have done that, What The Heck???"

Glad you found it.

Tom Albrecht · #44 04-09-2015, 10:59 AM

If it makes you feel better, I will admit that an electrolytic cap exploded in a set I was working on last night because I accidentally connected it to the filament pin rather than the cathode. Just a little 5 uF guy, but still a pretty nice "pop." We all make mistakes! Good luck as you continue your project.

To adjust the range of the hold control, see my post further up this thread about changing the value of the resistor in series with the hold control.

timmy · #45 04-09-2015, 11:34 AM

Quote:

Originally Posted by Tom Albrecht

If it makes you feel better, I will admit that an electrolytic cap exploded in a set I was working on last night because I accidentally connected it to the filament pin rather than the cathode. Just a little 5 uF guy, but still a pretty nice "pop." We all make mistakes! Good luck as you continue your project.

To adjust the range of the hold control, see my post further up this thread about changing the value of the resistor in series with the hold control.

well what i just did was take out the 3.3meg and put a 2.2 meg and its fine and got range on both sides. and i put the 220k resistor in for the blanker and those lines are history, again thanks alot...