Capacitor question - Videokarma.org TV - Video

freakaftr8 · #1 10-28-2007, 07:13 PM

Hey guys,
on my ctc-16 off the vertical and IF boards there are two caps. These are white and cylyndrical. I know there wax paper, at least it seems. There rated at .001mfd 2kv. Im not too sure, but I think there polarized, there s a black band on one side. they attach to chassis ground then to the board. I feel these could be the culprit to the shrinking vertical issue and the smeared chroma issue I am having. Do you know if these are polarized? Ive seen them being replaced tinh sprauge orange drops before, but until my millimeter gets here (and I have no idea how to test with it) im dead in the water.
Thanks

julianburke · #2 10-28-2007, 07:54 PM

Quote:

Originally Posted by freakaftr8

Hey guys,
on my ctc-16 off the vertical and IF boards there are two caps. These are white and cylyndrical. I know there wax paper, at least it seems. There rated at .001mfd 2kv. Im not too sure, but I think there polarized, there s a black band on one side. they attach to chassis ground then to the board. I feel these could be the culprit to the shrinking vertical issue and the smeared chroma issue I am having. Do you know if these are polarized? Ive seen them being replaced tinh sprauge orange drops before, but until my millimeter gets here (and I have no idea how to test with it) im dead in the water.
Thanks

They are polarized and the black band is the (ground) marked side.

ChrisW6ATV · #3 10-29-2007, 01:04 AM

Strictly speaking, older caps often had a black band to designate "outside foil". That end was usually connected to ground as a form of shielding in bypass or similar applications. It is not true polarization; that is, you could reverse the connections and it would not make the cap fail/disintegrate as with electrolytics.

Allied or Just Radios are sources of replacement high-voltage caps.

freakaftr8 · #4 10-29-2007, 11:39 AM

Well I went to my local electronics shop today and located a 1.5kv .001mfd non polarized square film cap. these are blue and rectangular, thinking ill give it a shot. Besides what am I out if it doesnt work out? More problems?
lol

Findm-Keepm · #5 10-29-2007, 12:15 PM

I'd hold out for the 2Kv rated capacitors- RCA engineers specified the voltage rating for a reason, I'm sure. Sprague/SBC makes them - search on part number 20PS-D10 for the .001 2000V capacitor. Several web outlets have them, if you can't find them locally.

Mallory (in their PVC "orange drop" version) doesn't go that high, and stops at 1600V.

Cheers,

freakaftr8 · #6 10-29-2007, 04:52 PM

Thanks for that info Brian, I got 'em on order today.. You probably saved me from blowing the poor set sky-high!

freakaftr8 · #7 11-05-2007, 11:07 PM

Hey any of you guys ever have ceramic disc caps go bad? I have one that feeds the b-y. It's a .01 and it's about 8mm in dia. does that mean .01 mfd? or is it pico? whatever it is it registers as .33.

jpdylon · #8 11-06-2007, 01:12 AM

I would not go replacing caps following assumptions. THe problems you are facing are due to defective components, but you need to properly troubleshoot the set before you can come to a conclusion as to what part is really at fault. Do you have a schematic and a receiving tube manual? If so you can compare voltage readings on the tubes with what is in the schematic. If something is terribly wrong (ie 2v where it should be -10) it can be easily determined what is causing it. I can send you a scan of the IF and video sections of the CTC-16 chassis if you can give me an email address.

Unless you like throwing money at caps you may not need, you really need a good capacitance tester that measures leakage. Simple digital multimeters aren't good enough because they do not supply enough voltage to cause the suspect cap to malfunction. A real capacitance tester will put anywhere from 1-1000v through a cap to ensure there is no leakage. Sometimes you can use an old VTVM and use it on the AC function to measure leakage on a capacitor. An ESR meter is good as well, but only really for electrolytics and no for film mica, or ceramic caps.

The ceramic and films caps do not fail as often as electrolytics, but they do fail. If there is smearing on a black and white picture as well as color, I would look to video and IF circuits. YOu can take out the bandpass amp, color amp and 3.58 tubes to render the color circuits inoperative. This may better help you to isolate the video smearing problem.

The vertical shrinkage is attributable to drifting grid resistors on the vertical output tube, and faulty electrolytic (big silver can on the vertical board) As a precaution if I experience that shrinkage problem I will shotgun the board with all new caps and check the resistors on the board for drift. Its ok to see a slightly lower resistance than the printed value while in the circuit board. However, if the value taken is more than 10% of its actual printed value, the I will replace it.

freakaftr8 · #9 11-06-2007, 10:59 AM

Thanks for the input on that, it's good to know that others are keeping up to date on my project (that my wife shakes her head at). lol, but heres the scoop. I bought this digital capacatince meter and it seems to work well, but I noticed with it's better to lift one leg off the board to test. What I have noticed is that after I replaced all the lytics in the power supply, I tested the new caps last night in which 3 of them are 450v 100mfd instead of the original can cap rating of 450v 80mfd. One cap reads 147mfd. I have schematics on this set and I am fairly intellegent on reading them however there are just a few things I need to brush up on..

Quote:

Originally Posted by jpdylon

I would not go replacing caps following assumptions. THe problems you are facing are due to defective components, but you need to properly troubleshoot the set before you can come to a conclusion as to what part is really at fault. Do you have a schematic and a receiving tube manual? If so you can compare voltage readings on the tubes with what is in the schematic. If something is terribly wrong (ie 2v where it should be -10) it can be easily determined what is causing it. I can send you a scan of the IF and video sections of the CTC-16 chassis if you can give me an email address.

Unless you like throwing money at caps you may not need, you really need a good capacitance tester that measures leakage. Simple digital multimeters aren't good enough because they do not supply enough voltage to cause the suspect cap to malfunction. A real capacitance tester will put anywhere from 1-1000v through a cap to ensure there is no leakage. Sometimes you can use an old VTVM and use it on the AC function to measure leakage on a capacitor. An ESR meter is good as well, but only really for electrolytics and no for film mica, or ceramic caps.

The ceramic and films caps do not fail as often as electrolytics, but they do fail. If there is smearing on a black and white picture as well as color, I would look to video and IF circuits. YOu can take out the bandpass amp, color amp and 3.58 tubes to render the color circuits inoperative. This may better help you to isolate the video smearing problem.

The vertical shrinkage is attributable to drifting grid resistors on the vertical output tube, and faulty electrolytic (big silver can on the vertical board) As a precaution if I experience that shrinkage problem I will shotgun the board with all new caps and check the resistors on the board for drift. Its ok to see a slightly lower resistance than the printed value while in the circuit board. However, if the value taken is more than 10% of its actual printed value, the I will replace it.

ChrisW6ATV · #10 11-06-2007, 01:12 PM

Yes, you need to test capacitors out of the circuit for anything other than a short, in most cases. The only test that is usually reliable in-circuit is for ESR in electrolytics. Resistors can be measured in-circuit to some extent, to test for increased resistance (or open of course).

The disc capacitor you mentioned is .01 microfarad. Values with a decimal number are always in uF, whole numbers are in picofarads (once called uuF) More recent caps have been marked with a 3-digit number representing the value in pF. The first two digits are the value and the third digit is the number of zeroes after the first two. (473=47000 pF=.047 uF.)

I have found bad disc caps a number of times in my work (and Mylar/film types too), but not nearly as often as electrolytics.