CTC-15 restoration

[mstaton]

I had a set that did a similar thing. If I turned the contrast one direction it looked like this(see thread: http://www.videokarma.org/showthread.php?t=252862) but id I turned it the other way, I got a weak but full raster. ALL the canned electrolytics were dry. Good HV and B+, screen volts OK.

[6GH8cowboy]

The quad E-can at the end has been replaced (bad seal, dripped, dried out) others are OK. I have subbed to make sure any way. Replaced the .1 on the agc line to the IF strip and the video from the detector looks more stable on the scope. Looks good going into the 12BY7, bad coming out I may just shotgun all the related components and reflow all the joints. I hate black magic fixes like that, I would prefer to know what exactly the fault is, but this is getting time consuming for this one problem alone and I have not yet seen what other things will have to be addressed.

[DaveWM]

screen resistor/contrast pot/service switch for trouble with the Video out.

I have also replaced the grid coupling cap on the video, but if you are good at the grid then that should not be a problem, unless is just a bit leaky. That "could" account for the low plate voltage. I know you did voltage checks but don't remember the results.

I am assuming the 50uf cap on the contrast control is not shorted.

[6GH8cowboy]

Brief raster on the left dark screen with close focus. Drum roll please


The focus rectifier! Likely shorted. After seeing decent signal on the scope (after soldering all the parts in the area and grounds I still had the strange symptom yet wave forms and DC on the CRT grids and cathode looked good. The last thing to ponder "the focus grid. The voltage was a bit rich in AC content so a rectifier change was in order. I also discovered the previous person had a 100 ohm resistor in place of the 1 meg in series with the focus lead also.

I now have a picture in near focus but a unresponsive focus control. I can now view a picture and see there is much to do like AGC and sync issues. Vertical gain next, then color. The CRT is looking decent but the cap is scary loose and I've had to re-flow the solder in some of the pins.

Any suggestions to secure the base to keep it from moving short of JB weld? I don't want wires to break from movement

Progress is being made

[DaveWM]

if there is still some of the brown glue left but just not stuck, I have had luck with a product called "flex zap" you can get it at model shops. Its a kind of CA glue but has some give to it so as not to shock break in heat cycles.

If the focus is not responding, 1st check the focus voltage and make sure you are getting an adjustment of at least 500v. I use a simpson 260 in the 5kv mode.

does the focus coil look cooked?

[6GH8cowboy]

Focus coil looks OK. I am going to check the value of the HV cap between the coil and the stick. I have run across a number of creative part subs so far.

As far as the CRT base cap goes I want secure it against mechanical movement but would like to have the option of getting behind it in the future if a last ditch (desperate) effort is needed by somebody. My concern is that even slight movement over a long period of time will lead to wires breaking off at the nibs. Present servicing and restoration just adds to the problem as the chassis is reconnected for testing and repair at present.

[DaveWM]

I think the flex zap will fill the bill. Never tried to break the bond after using it, but I suspect it would not take a lot.

when you were having the dark CRT before, I thought you said you had checked the focus voltage?

I have not seen a bad 130pf but that does not mean much as I have not been doing this long. Did you get a chance to see if the focus voltage varies at all with the coil? If not I would think one of the coils may be open. the way I understand how it works is sorta like an adjustable bucking transformer, two coils out of phase, the core simply moves from the out of phase to the in phase thereby adding or subtracting to the pulse from the fly that is then rectified by the stick. the 66meg is a load and the cap a filter.