CTC-7 Time

[Eric H]

Hey all, well I finally wheeled the 7 out to the dining room in the hope that I will be inspired to fix it.

Things are looking better already, I had thought there was a video problem because all I could get was a washed out picture but... I had only tried it on rabbit ears up till now.

Tonight I hooked it up to a VCR and viola! a good picture.

The purity is lousy, the convergence is fair for a quickie adjustment, it focuses right in the middle of the control

Not a hint of color to be seen, any ideas where I should start to fix that?

[jstout66]

I know this sounds pretty elementary, but have you checked every tube in the set? I've run into problems with the early RCA's, that if a tube is bad, even in a different circuit, it can throw things "off". One time I had a bad horizontal osc tube in a CTC-16. The horizontal was fine, but I had no color!! That was the only bad tube in the set, so I changed it, and guess what??Color!! It also sounds like you need to adjust the AGC control if it made that a big a difference from rabbit ears to cable. Also the 3.58 osc may be bad..... And this is just my opinion, but I notice some people tend to think "worst case scenario" when working on these sets and start ripping everything apart, without checking the simple stuff first. It's best to start out with checking every tube, and go from there. There still are some sets out there that need very little work to come back to life... Good Luck!

[Rob]

Eric,

You need a new picture tube. That one has run out of color!

jstout66 is right, you should check the tubes. Have you tried rocking the horizontal hold back and forth to see if changing the burst gate timing gets color to snap in?

[wiseguy]

eric,make sure you do have a color signal going in,i would start off
with rocking the fine tuning control from one extreme to the other and see if you get color bars floating around,one other thing is those boards and intermitt connections,with tuning at peak sharpness adjusted then start pushing around on the boards and tubes to see if any changes happen..just dont burn your hands and use a large mirror for starts,this is about the only thing before taking the chassis out and troubleshooting..i did this on my ctc-7 and found all kinds of intermitt problems with bad solder joints,my set still looses filaments on the vert output tube,and its not the tube,make sure all the filaments are lit,and tubes are good..good luck and drink a lot of wine before you do this!
terry

[Eric H]

OK, I'll check the tubes tonight. Most of the tube shields are missing also so I will have to scrounge some up.

The 3.58 crystal is the type in a 7 pin tube envelope, were these prone to fail more than the metal ones?

[kc8adu]

color killer misadjusted?

[Eric H]

Terry, a VCR should provide a color signal that will work?

I checked all the tubes in the color circuits, someone had subbed a 6GH8 in place of one of the 6U8's. I didn't have one handy so I swapped it into the other position but made no difference.
I would think this would be an acceptable sub?

I twiddled the killer trimmer, the fine tuning, the horiz hold and nothing I did produced anything at all. There is no color snow, rainbow bars or any hint of color at all.

Would this suggest the 3.58 osc is not running?
I guess I'm going to have to pull the chassis and rig it up so I can run it and access the underside.

(Note: the chassis has been completely recapped)

I did manage to get my hand across the fuse but I'm running an isolation transformer so it only went through one hand.

Rob, your right, the CRT is pretty soft, it has that shiny look at the base from having a million hours on it.
I will probably wind up putting the rebuilt FBP (JP?) in after I get the chassis fixed.

[Chad Hauris]

It appears to me that the 3.58 osc is not working. Measure the negative grid voltage on the oscillator section of the 3.58 osc. tube. It should be around -7 volts. I had a bad 3.58 crystal in one set...hooked up a known good xtal w/alligator leads and got color.
Also the plate voltage on the osc. tube will be high because the tube is not drawing any current through the load resistor if not oscillating...make sure also that there IS plate voltage at the tube. Do you have the photofacts/schematic...it's a lot harder to do this troubleshooting without it.

[Eric H]

Here's where i'm at.

I bought a new 3.58 crystal just to eliminate that and it made no difference.

I think I might have an open Burst Phase Transformer.

Referring to the picture, pin 9 of the Burst amp 6AW8 has 450v
pin 8 about 390, all too high. Pins 1 and 3 of the 6BN8 Phase det have 42 volts instead of the 13 called for.

I have cont across terminals A & F of the BP trans I also have cont across terminals E & C but nothing from either E or C to terminal B
It looks like it should have continuity across all three, yes?

Does anyone think an open transformer here would cause the high voltages I'm seeing?
I guess I will have to remove the Tformer to do a more detailed test and hopefully be able to fix it if it is open.

[Rob]

Eric,

Do you see where there is a 270 volt power supply port that R726 gets power from and drops it to +260 volts for the Burst Amp? I'd go looking to see why that +270 volt supply rail is so high.

[Eric H]

Rob,

It appears to come directly from the power supply.
The schematic shows a 270v and a 382v source.

I will investigate and see how much it is right at the source, but first, dinner!

[rcaman]

from looking at the schematic you should have a reading where you are not on the coil. it looks like you found one of the problems.
a bad coil or transformer wichever you want
to call it. steve

[Kirk]

I had this exact problem when I recapped a CTC 7A.

The burst ckt was so far off freq after I replaced the 2 coupling caps to the Phase detector (6AL5) that there was no chroma info at all.

Do you have Meaghers' RCA Pict-O-Guide? As a former RCA Service Tech I ALWAYS refer to this publication when I have chroma/sync problems. It has some great techniques for nailing down these nasties WITHOUT expensive test equipment. It was meant for feild techs to make repairs in the home.

The best one is the 1964 version (White cover) or the 1957 version (Black cover). I have both if you would like pages copied.

I used his method for finding the problem, and it was an adjustment to the burst transformer. DO NOT START ADJUSTING COILS! Follow the book and you will find the problem.

Best of luck,
Kirk

[Eric H]

Hi all, thanks for the ideas.

I was wrong about the transformer being open, I just wasn't checking across the right pins.

Tubes are all good, I found a 6U8 and replaced the 6GH8 but it didn't make any difference.

I've been too busy and tired to do any more with it this week.


Kirk, I don't have a Pict-O-Guide but I do have the RCA TV Service Clinic book for this set.

It has schematics and all the info for setting the set up in the home including HV, Horiz Efficency, Purity etc... but I'm not sure about the color oscillator, I'll have to look and see.
I have the Sam's also.

I would sure appreciate a copy of those Pict-O-Guide pages, can you scan and E-mail them or will you need to Snail mail them?

Thanks,

Eric