CTC-10 adjustment lug?

[frenchy]

I am finally back to this remote-contolled CTC-10W giant that has been pining away in my garage till I had room in the house to bring it in and work on it. The basic problem I have right now is no color - black and white is fine, and locks on the color signal, but once locks in all I get is varying intensities of purple in the picture instead of all colors. Tint control doesn't change it at all.
But first I have a question about this adjustment lug that's on the top side of the chassis in the color demod section, a grounded wire that can be plugged into two different positions. I can't seem to locate this thing on the schematics and want to make sure this is original, or not, and what it does, before I rule it out as possibly having an effect on the color section. Attached is a picture, lug is right in center of pic. Center lug = ground, two on either side are the adjustment plugs, two more on ends of lug go to wires and have a resistor bridged across them. thanks!

[Chad Hauris]

If the picture is just purple and you can vary the intensity of the purple by using the color control then the chroma signal channel is working but the 3.58 mhz oscillator is not. Check the grid of the 3.58 osc tube and make sure there is the appropriate amount of negative grid voltage. No voltlage means the oscillator is not running. One time I had a bad 3.58 crystal.

The tint control works by changing the phase of the locally generated 3.58 signal with respect to the phase of the transmitted signal so when the 3.58 osc is not working the tint control won't do anything.

Am not sure about the adjustment lug but it probably wouldn't have an effect on your problem. Track down what it connects to in the demod circuit.

[frenchy]

I had gone thru it before and checked for opens on the coils just using an ohmeter in circuit and didn't find any opens. Also tried clipping another 3.58 crystal (a tube one from my CTC-5) with no change. So still poking around in it trying to figure out why I don't have any oscillating going on here. I may have to buy an oscilliscope to figure this one out. I will try checking the grid voltage with the voltmeter....Frenchy

[Chad Hauris]

I had this problem in a ctc-15 clone but it has been several years and I can't remember what the exact fix was. I know I replaced the crystal but it seems like there was an open coil in the osc. section. I think I salvaged one out of another ctc-15 clone chassis and that did the trick. Would probably be good to check all the voltages at the 3.58 osc tube.

I think I did use a scope to try and check out the 3.58 signal but it doesn't really seem like a necessity...the dc voltage readings should lead you to the trouble.

[frenchy]

OK I just measured some pins on the 6gh8 oscillator tube:

pin 6 should be 222v, measured about 160
pin 3 should be 148v, measured about 100
pin 2 should be -5.8v, measuread less than -1 volt
pin 1 should be 54v, measure 60 (ok?)
pin 8 should be 2.2, measure 2.5 (ok?)
pin 9 should be 0.5 v, measure less than 1 volt (ok I think)

So the ones on the oscillator side of this tube seem off as opposed to the side that is in reactance circuit. This was measured with the existing crystal as I didn't see a change with a tube crystal clipped on top of it. The two 47k resistors on either side of the crystal measure correct ohms. Does this sound like maybe the 3.58 coil? Maybe measuring with an ohmeter was not sufficient. Someone had sugested this coil as a possibility before. I don't have any other problems with the set as per has good black and white, sound etc. Thanks!

[frenchy]

Oh yeah and this tube checked good on my Heathkit tester and I think I even swapped it out with no change.

[Chad Hauris]

It's not a good idea to parallel the crystals in my opinion, just hook up the known good one and remove the old...it could have leakage that is loading down the circuit.

I'll try and look at the field service guide later today and see if I have any more suggestions.

[oldtvman]

any time you have a problem with an oscillator circuit in one of these oldies, it's best to go in and shotgun the circut with new caps, it takes a lot less time to do that than to try to figure out which one is leaky or off value.

[frenchy]

I have only replaced the one 40mfd filter one, C729, in that area, as all the other caps look to be the hard brown type, not paper. Original or not, I don't know. Can anybody take a look at the schems and lemme know which ones would fall into the shotgun approach for this oscillator? There are about eight or so .01 caps around that tube, I suppose I could just start with those. First I will retest it with the new crystal/no old crystal, and recheck the osc. coil just to be sure I measured it right before. Thanks!

[frenchy]

And one more thing, looks like that adjustment lug is on the schematics, it just changes between lugs on the vertical output transformer, but it doesn't say it's purpose. It's on one of the three output windings that feed right into the convergence board plug. The set already has vertical height, linearity and centering pots, so what is this extra tap for?

[Chad Hauris]

Here is the chroma section of the ctc-10:

http://www.retroaudiolab.com/sams/rcactc10.jpg

also it says about the jumper:

"Change jumper to ground bottom side of winding when more vert. tilt range is needed for optimum convergence".

[frenchy]

Some more bench testing with the flyback fuse removed:
Clipped one leg of crystal - voltages did not change in osc. section.
In-circuit ohm readings on oscillator coil with set off:
D to A = .3 to .4
A to F = .5
B to C = 7.0
Between D/A and A/F windings = 10K range and rising (charging a cap somewhere)
There are a bunch of big disc-type caps in there instead of the usual mylar ones, they say "10,000 WV 244". Are these .01's? Can I replace them with regular 600v jobs or do I have to use 10,000 volt ones? Reason I ask is schematics etc. that I have don't list voltage values of the caps, so not sure. Don't know if I just don't have a copy of that part or it wasn't printed. Anybody have a listing of that for ctc-10? This would be for caps from about C700 to 730. Didn't look like a high voltage area so wondering why such big V caps used. Thanks!

[frenchy]

<<<I'm also puzzled by the voltage values you gave for 6GH8 V20 and the values listed in the schematic Chad posted. You say that "pin 2 should be -5.8v" where the schematic Chad posted has pin 2 at -.5V. It's a problem.....>>

I just noticed that. My measurements actually sort of match up with the above schematics but the numbers on MY schematics are different (?!) I'm using schematics etc. that were sent to me by some nice person in here I can't remember who. On top it says "circuit diagram for ctc-10A, B, C........W. Mine is a 10W. So right now I'm confused also and not sure why my schematics match the chassis but the readings on it don't....Frenchy

[blue_lateral]

There are a bunch of big disc-type caps in there instead of the usual mylar ones, they say "10,000 WV 244". Are these .01's? Can I replace them with regular 600v jobs or do I have to use 10,000 volt ones? Reason I ask is schematics etc. that I have don't list voltage values of the caps, so not sure. Don't know if I just don't have a copy of that part or it wasn't printed. Anybody have a listing of that for ctc-10? This would be for caps from about C700 to 730. Didn't look like a high voltage area so wondering why such big V caps used. Thanks!

My ctc10 schematic lists c701, c703, c710, c719, c725, c727, and c730 as .01 +100% -0% 500v. It doesn't mention what type of ctc10 it is (a, b, w, etc...)

John

[frenchy]

I'm definitely looking at the right tube, labeled ctc-10...W chassis, the V703 a and b, 6gh8 marked as the 3.58 oscillator/reactance control. Pin 2 says -5.8v instead of -.5, pin 6 says 222v instead of 185, pin 3 says 148v instead of 110 etc., all pretty different that the ctc10 schems posted in the thread. Even the 250v feeding into both sides at the bottom say 275v on mine. I don't have a scanner working right now but I will try to see if I can get a pic of these schems posted, the printing on these looks more handwritten but don't see anywhere what company printed them. They include partial parts listing, tube layout, tuner adjustments etc. The part values seem to be the same on both, just the voltage readings look different. Anyway, the voltages I measured don't seem that far off from those other schematics (within 10%) so now wondering if they themselves still indicate a problem or not? Arghhh I got enough problems with no color, now I'm getting crosseyed with two schematics! Which ones right? : / Frenchy