CTC5 Pickup!

[Yamamaya42]

If it was not running, you would have the telltale greenish hues when you turn up the color, can post a pic later.

[Davala]

Originally Posted by Yamamaya42

If it was not running, you would have the telltale greenish hues when you turn up the color, can post a pic later.

Interesting.... I figured without the crystal running I would have no color. I have good greyscale tracking but zero color. If I move the hue control there is a tiny change in the grey but that's it.

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Matt Davala

[Yamamaya42]

https://i.imgur.com/9HcgQcz.jpeg


This is what My CTC-16XL was like with the crystal disabled!

[old_coot88]

When the 3.58 reference signal is missing, the chroma signal cannot be demodded in phase but only in amplitude, so it's displayed as just that yukky green color. Has to do with how the signal's phase is baselined.

[Davala]

Yay! Or maybe not yay... I found an open 6.8k 7 watt supplying B+ to the first chroma tube. R172. Above the resistor the chassis looks rather dark. I'll ohm out the transformer that connects to the plate. What the heck caused that to get so darn hot?

EDIT: I do have continuity through the transformer to plate. I do not have a 6.8k in stock unfortunately. I miss being able to buy stuff locally.

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Matt Davala

[Yamamaya42]

I can't tell for sure from the low res pics in the sams, but it may look like the set has many paper caps, and if it does many may be bad and leaky and need replacing, if C142 is very leaky, it could very well have toasted the resistor.

[Davala]

Originally Posted by Yamamaya42

I can't tell for sure from the low res pics in the sams, but it may look like the set has many paper caps, and if it does many may be bad and leaky and need replacing, if C142 is very leaky, it could very well have toasted the resistor.

I wouldn't think the ceramic cap C142 would be bad, but I have no capacitor tester. How critical is it really that I couldn't sub in a modern .01 orange drop equivalent?

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Matt Davala

[Yamamaya42]

If it's ceramic, then the chances are rather small that it's shorted, but not unheard of, the DO short, but it's really rare, as mentioned above, I could not see clearly what kind it really was, you will know rather soon if the new resister starts to heat up way to fast if something took it out like a short or something.

But if there are paper ones in other areas, best not to trust them.

[Yamamaya42]

Example, there looks to be a bumblebee capacitor on the horizontal PCB, cant see what the others are. :O

[Davala]

Originally Posted by Yamamaya42

Example, there looks to be a bumblebee capacitor on the horizontal PCB, cant see what the others are. :O

It's all been recapped... At least 45 capacitors. Wowiee. Maybe my Dumont ra-103 had more but I'm not sure!

[Davala]

I love finding former wierd repairs... I was investigating why I need more focus range so obviously I check resistors after the 1v2. The bleeder resistors were all high, they should all be 10meg. One was 16 meg, one 14 and the other actually close at 11 meg. Not an issue there as I did buy some 10meg two watts. Being NOS resistors most tested high so I found the ones closest to 11megs each. None were bang on 10, not even close. I'll get those in after I finish this post..

The former technician repair job that surprised me was the bit of wire jumping over the two 1 meg load resistors R155 and R156. I removed the jumper and tested the resistors and they are spot on 1 meg. The other bodge I found was a ceramic cap from the 1v2 cathode to ground. A bit of filtering perhaps? It looked crunchy and they ripped part of the cap where the wire leading into the cap goes. I tossed it. No value printed I could find.

Is this another CTC-7 mod they were applying or was this them being lazy because they didn't have 10 meg bleeder resistors in stock?

I'll have to wait a couple days to get the chassis back in to evaluate these issues with the focus and to see if my R172 replacement gets my color to return. I'm waiting on some .01 ceramic caps to replace the ones going to V22 as they looked bubbly and hot. I want to reduce my chances of burning out my replacement 6.8k R172 replacement.

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Matt Davala

[wkand]

Originally Posted by Davala

It's all been recapped... At least 45 capacitors. Wowiee. Maybe my Dumont ra-103 had more but I'm not sure!

There were some RCA black and white sets 20 inch and above, in the 1950s, that had over 50 wax caps. RCA loved them waxies. Part of that is the belief that tubular capacitors automatically have more consistent high frequency response. Admittedly it is much harder to properly select ceramics for high frequencies.

[Yamamaya42]

This is the point where an oscilloscope would be extremely advantageous to finding such a problem.

Looking for the correct signal starting at the color takeoff coil (L36) and seeing if W23 is correct or not, (taken with color rainbow input), then onward to W24 at the color control, (bandpass 1 out), and next W25, (bandpass 2 out).

This should give some idea as where you are losing color.

[Davala]

Originally Posted by Yamamaya42

This is the point where an oscilloscope would be extremely advantageous to finding such a problem.

Looking for the correct signal starting at the color takeoff coil (L36) and seeing if W23 is correct or not, (taken with color rainbow input), then onward to W24 at the color control, (bandpass 1 out), and next W25, (bandpass 2 out).

This should give some idea as where you are losing color.

L39 primary was open. I removed the transformer ungracefully(I'll have to hot glue it back in place.. oops) and saw the issue. It is carrying plate voltage for the second bandpass amp. With such fine hair RCA used as wire it vaporized at some point in time. I should have asked my wife for a magnifying glass but I searched and saw the tiniest smidge of wire coming out of the transformer. I really had no hope of saving this transformer so I just went all out with solder and a 1 piece of copper wire. Melted the heck out of where I suspected the lead to be and after a half dozen tries I now get continuity through the primary. 8ohms just like the good book said it should be. Will it hold up? Doubtful but I tried.

Guess I'll get it back in and see what happens...

Where can I get a backup transformer? Only an RCA part number 102259, no one else made a replacement.

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Matt Davala

[Davala]

Finally I got it. Seems my transformer "fix" is holding. Definitely seems like its drawing just a bit more power than it should at 117volts. 400-410 watts. Almost 3.85 3.9 amps...

I'm finally bringing this into the house to finish the convergance adjustments. I'd been on the ground in the garage and its very uncomfortable. My wife wants to put in in our living room replacing our 1955 B/W set we'd been using for well over a year.

I'm sure I'll be back on here soon whenever the next part fails! The set is going to cook with the back cover on.

Thanks everyone for putting up with my posts!
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Matt Davala