Looks like someone wrote on the back, CTC90D. Anyway, just got this from a guy that was a tv tech who had kept up maintenance for years. It doesn't have any color to it and it has a bit of convergence issue near top. Just looking where to begin. Want to use this set with matching vcr, ced unit and atari.

I've been looking at this for a bit. Due to the move from where I picked it up, an hour away, the yoke had slid back and shifted also causing the purity rings to get pushed back to the socket. I've put everything back up where it should be but I still have nearly no color and convergence is a little off.

I've been looking at this for a bit. Due to the move from where I picked it up, an hour away, the yoke had slid back and shifted also causing the purity rings to get pushed back to the socket. I've put everything back up where it should be but I still have nearly no color and convergence is a little off.

Maybe there's an issue with the color control? I would pull it and check resistance across the pot and make sure it's not flaky.

Maybe there's an issue with the color control? I would pull it and check resistance across the pot and make sure it's not flaky.

The dial at the front behind the door?

The dial at the front behind the door?

I'm not familiar with you're specific set, but there should be a color control on it. When you turn the color down all the way, it should make the image black and white. It essentially is there to let you adjust the chroma subcarrier level.

If there was something wrong with the control, like there was a break in the carbon track, or it was just really dirty, or there was a bad solder joint or something, that could cause a loss of color like you are seeing.

Another thing that could cause loss of color is if the the tuning is off and you are using RF. Sometimes if the tuning capacitors are dirty, that can cause weird effects like loss of color. That generally just requires spraying the tuner and moving it back and forth a bunch. This would only be an issue if you're using RF input, not if you're using composite.

There's plenty of other possible issue though. It could be a bad component in the chroma demodulation section or a bad power supply source voltage for one of those areas. I'm just giving you low hanging fruit to test

I'm not familiar with you're specific set, but there should be a color control on it. When you turn the color down all the way, it should make the image black and white. It essentially is there to let you adjust the chroma subcarrier level.

If there was something wrong with the control, like there was a break in the carbon track, or it was just really dirty, or there was a bad solder joint or something, that could cause a loss of color like you are seeing.

Another thing that could cause loss of color is if the the tuning is off and you are using RF. Sometimes if the tuning capacitors are dirty, that can cause weird effects like loss of color. That generally just requires spraying the tuner and moving it back and forth a bunch. This would only be an issue if you're using RF input, not if you're using composite.

There's plenty of other possible issue though. It could be a bad component in the chroma demodulation section or a bad power supply source voltage for one of those areas. I'm just giving you low hanging fruit to test

Ill check into it. I really don't know at this point. I dont even see tuning. There's only a coax and 2 sets of screws.

I believe the black plastic piece around the channel knob comes off for access to the fine tuning pots.

I believe the black plastic piece around the channel knob comes off for access to the fine tuning pots.

Wow, awesome!! That was hidden well.

No changes with tuning.

Open up the door at the bottom of that panel and take a picture of the color control. Make the picture larger. Your other pics are too small.

Open up the door at the bottom of that panel and take a picture of the color control. Make the picture larger. Your other pics are too small.

https://i.postimg.cc/fLbFDynz/20260812-082256.jpg (https://postimg.cc/SXwVGyx3)

That's it. What happens to the image when you swing that color pot from end to end? Nothing at all?

The color pot is the one on the top right just to be clear.

That's it. What happens to the image when you swing that color pot from end to end? Nothing at all?

The color pot is the one on the top right just to be clear.

Yeah no change at all.

Yeah no change at all.

In that case, I would remove the control from the circuit and test it for continuity with a DMM.

If you can rule out that the control as a problem, then you can focus on other things.

Assuming the control is okay, then my next step would be to check from the chroma signal out of the demodulation area. I personally wouldn't attempt it without a schematic though

There are other guys on this forum who might be able to point you at some part to check after that or not, but it's going to get increasingly more complex as you rule out low hanging fruit like a bad control

In that case, I would remove the control from the circuit and test it for continuity with a DMM.

If you can rule out that the control as a problem, then you can focus on other things.

Assuming the control is okay, then my next step would be to check from the chroma signal out of the demodulation area. I personally wouldn't attempt it without a schematic though

There are other guys on this forum who might be able to point you at some part to check after that or not, but it's going to get increasingly more complex as you rule out low hanging fruit like a bad control

You mean that top left looking from the back? Also looks like its had a history with color problems. Some changed the board out and left the old one inside...

https://i.postimg.cc/nzBkz7kC/20260813-180107.jpg (https://postimg.cc/njV7SXNJ)

https://i.postimg.cc/9FWpmDwS/20260813-180120.jpg (https://postimg.cc/s1NSKDc9)

https://i.postimg.cc/7Zhnzj9D/20260813-180127.jpg (https://postimg.cc/gx9hFS1B)

You mean that top left looking from the back? Also looks like its had a history with color problems. Some changed the board out and left the old one inside...

Yes. You can probably get a decent idea of how it's working by measuring it without taking it out first.

Take you multimeter and measure across the whole pot to see what the resistance is, and then measure between the wiper and either side. find a way to clip the meter leads onto the terminals of the pot and turn the pot from side to side while looking at the meter. You should see the resistance change smoothly from one end of the pot to the other.

Based on what you have already said though, I would expect it to be completely shorted, or completely open if there's a problem with it at all.

If you can confirm that's it's behaving like a normal pot, then you can pretty much assume it's not broken and move on.

Looking at those other pictures, it seems like those old boards might need all the connectors cleaned really well, and the solder joints reflowed on anything that looks bad or is a physical connector.

Solder joints tend to fail on parts that are either heavy or take abuse, like connectors that get done and undone, and big heavy parts like the flyback or transformer, or big power resistors. You also want to check things that get hot, especially if they have been darkened or burned.

A lot of these kinds of issues will come down to basic stuff like that. Anything more advanced is probably going to require schematics.

Yes. You can probably get a decent idea of how it's working by measuring it without taking it out first.

Take you multimeter and measure across the whole pot to see what the resistance is, and then measure between the wiper and either side. find a way to clip the meter leads onto the terminals of the pot and turn the pot from side to side while looking at the meter. You should see the resistance change smoothly from one end of the pot to the other.

Based on what you have already said though, I would expect it to be completely shorted, or completely open if there's a problem with it at all.

If you can confirm that's it's behaving like a normal pot, then you can pretty much assume it's not broken and move on.

Looking at those other pictures, it seems like those old boards might need all the connectors cleaned really well, and the solder joints reflowed on anything that looks bad or is a physical connector.

Solder joints tend to fail on parts that are either heavy or take abuse, like connectors that get done and undone, and big heavy parts like the flyback or transformer, or big power resistors. You also want to check things that get hot, especially if they have been darkened or burned.

A lot of these kinds of issues will come down to basic stuff like that. Anything more advanced is probably going to require schematics.
Before we get ahead of ourselves, what im wondering is did the color get affected by the yoke and rings being pushed back toward the socket? I've since moved everything up against the tube and straightened the image but I still have convergence issues as well.

https://i.postimg.cc/DykmRdY9/20260815-100129.jpg (https://postimg.cc/K4fZMLbf)

https://i.postimg.cc/XYxJGM7K/20260815-100138.jpg (https://postimg.cc/hXzg65mh)

https://i.postimg.cc/qqfMV4Q8/20260815-100150.jpg (https://postimg.cc/r0JL56Bm)

https://i.postimg.cc/bNhNmYZR/20260815-100158.jpg (https://postimg.cc/s1TrXr9B)

Convergence will not cause a lack of color. I would change that module you pictured. Most all of the color circuits are on it.

It would probably take an afternoon to test every component on the board and reflow all of the solder.

Of course, the IC on the on board could also be at fault, which would be harder and possibly more expensive to replace, but it's worth spending a day and making one perfect board to test with first

Without the schematics, I wouldn't know which pins on that IC to probe for a chroma waveform, but possibly one of the other guys here with more 70s TV experience remembers what IC it is and what it's doing

But first things first; lots of these issues can be just bad solder joints and/or toasted passives

Ill try pulling that board and see what's on the other side. Doubt I'd ever find a replacement. Better if I can fix one of these since there's 2 of them.

Ok, weird. Pulled board out and figured I'd put the old one in to see what happens. Had to set color and tint but here's what I got. Should I look at anything else before I close it up?

https://i.postimg.cc/Qx31bgQx/20260815-231631.jpg (https://postimg.cc/6TM86vbD)

https://i.postimg.cc/zGDWmJPn/20260815-231646.jpg (https://postimg.cc/yk5WczKd)

https://i.postimg.cc/9M9wPzzB/20260815-231710.jpg (https://postimg.cc/XGVv4jfZ)

https://i.postimg.cc/6qL7SSr2/20260815-231721.jpg (https://postimg.cc/MfHKf9rq)

https://i.postimg.cc/T3Py7tpD/20260815-231846.jpg (https://postimg.cc/kBkXDFNJ)

Ok, weird. Pulled board out and figured I'd put the old one in to see what happens. Had to set color and tint but here's what I got. Should I look at anything else before I close it up?

If it we me, I would pull and test every component on that little board, and replace anything that is out of spec (usually 20% for most components, maybe 10% for important resistors). The main concern I would have there is that the color board has an IC on it that could get stressed if some of the components have drifted too much, and that could be hard to find a replacement for it if it dies. 1970s ICs do not have a reputation for robust lifespan.

Also, your convergence is atrocious, so I would definitely dial that in with the yoke first. Caveat that yoke carries lethal voltages, so proceed at your own risk. Do whatever you have to do to learn how to handle it before you do anything.

If it we me, I would pull and test every component on that little board, and replace anything that is out of spec (usually 20% for most components, maybe 10% for important resistors). The main concern I would have there is that the color board has an IC on it that could get stressed if some of the components have drifted too much, and that could be hard to find a replacement for it if it dies. 1970s ICs do not have a reputation for robust lifespan.

Also, your convergence is atrocious, so I would definitely dial that in with the yoke first. Caveat that yoke carries lethal voltages, so proceed at your own risk. Do whatever you have to do to learn how to handle it before you do anything.

Not sure how to set convergence really. I've only ever done it on projection sets. Im guessing this is an in-line tube and I see what looks like 4 rings and a thumb wheel. Not sure what to do first.

Not sure how to set convergence really. I've only ever done it on projection sets. Im guessing this is an in-line tube and I see what looks like 4 rings and a thumb wheel. Not sure what to do first.

Explanation of the ring below, but first, I think you should check the yoke for slippage. Looking closely at your screenshots, I think the yoke probably slipped, and it's pointing up too much. You can see in your grid that the image gets bigger towards the top. I think it would be fixed if you pointed the yoke down and glued it in place. You can imagine the effect of moving the position of the yoke in the same way that pointing a projector at screen distorts the image if it's pointing up or down (or left or right). It's going to bow the image outward in the direction that the lens is pointed.

It can be very dangerous to move a yoke when the set is on. Make sure you know how to be safe. Consider just doing it in small steps while it's turned off and then checking it. It will take longer, but you also probably don't have the correct safety equipment to do this while it's on.

The rings (maybe):

I've never done an RCA before, but rings can be for both purity and convergence.

Purity is the color uniformity across the entire screen that is effected by how far the yoke is pulled in or out from the base of the tube's neck.

If you can imagine, when you pull the yoke in and out in line with the neck, the whole image will get bigger and smaller. However, the relationship between the position of the yoke and the tube will effect the spot that the beams land on the inside face of the tube because you are changing the geometry of the beam landing when you adjust the yoke.

The purity rings basically allow you to dial in the beam landing by giving you some whole-screen adjustment for the purity. You generally adjust this by 1. setting the purity rings to dead center, 2. putting up the three color (R, G, B) stripe pattern on the screen, and then pulling the yoke in and out until the stripes are dead even, 3. putting up an all white image and adjusting the purity rings until the image is totally white on the sides.

The convergence can be set by rings, but it can also be set by a potentiometer. This is almost always found on a box attached to the flyback or tripler, or it's found on the neck board. I've personally never seen one anywhere else. When it's a potentiometer, it's just the horizontal convergence, and the remaining rings set the vertical.

So what I think your rings probably are is two for the purity and two for the vertical convergence, and there's probably a dial inside somewhere that does horizontal. But that's just a guess based on other sets I've done from the same time period. I've never worked on an RCA before, and sets in the 70s tended to be less similar in design than they became later on.

Again, I've never worked on an RCA before, but I would guess that the rear two of the four rings would be the vertical convergence, just from experience. The rings closest to the base of the neck are typically the purity rings, assuming it has them.

If you do end up messing with it, I would recommend picking up some thick electricians rubber gloves to move the rings. They are not foolproof, but they will at least keep you aware of your hands and what you are touching. I personally still use them. I also use an isolation transformer so that the TV is not directly connected to the power grid.

Now its tilting down like it was when I got it. I dont see any change really but maybe you can.

https://i.postimg.cc/yxHhwKq5/20260818-195951.jpg (https://postimg.cc/8JZr6qzB)

Now its tilting down like it was when I got it. I dont see any change really but maybe you can.


Not really, no. Tilting the yoke enough in any direction will have an effect though, it absolutely has to. If you moved it and you got nothing, then you didn't go far enough.

Not really, no. Tilting the yoke enough in any direction will have an effect though, it absolutely has to. If you moved it and you got nothing, then you didn't go far enough.

It's as far down as it will go. Anymore would snap the neck. It's where it was when I found it. No wedges or support. I had moved it up after I got it but figured I had it too high because my shim was pretty thick.

It's as far down as it will go. Anymore would snap the neck. It's where it was when I found it. No wedges or support. I had moved it up after I got it but figured I had it too high because my shim was pretty thick.

That sounds wrong. Something was probably messed with before you got there, and the extra color board inside suggests they gave up on it.

I would assume that your set is not supposed to adjust with yoke movement if you're not getting any change. I know there are such designs, but I've not worked on one before. Sorry, I'm not there in person, so I made an assumption that I shouldn't have.

Looking at the pictures of your neck board, there appears to be knobs that relate to the convergence. I think that is where your solution lies. Do your best to document the effect of each knob before you go messing around with them. A good approach is to make a mark on the knob and the PCB so that you can return each one to it's starting position if necessary. Sometimes I will do that with tape so I can remove it when I'm satisfied.

Ok ill check these one at a time after I mark them.

https://i.postimg.cc/9F40yWmT/20260819-200430.jpg (https://postimg.cc/GHCbCnsh)

Start with the 3 white shafts that protrude through the board at 12 o'clock, 4 o'clock, and 8 o'clock.

Start with the 3 white shafts that protrude through the board at 12 o'clock, 4 o'clock, and 8 o'clock.

Will do.

Those 3 white one moved convergence around. Looks like that's ok but geometry is a mess.

https://i.postimg.cc/Bb0J5W4w/20260820-195652.jpg (https://postimg.cc/9RL3Vn4G)

https://i.postimg.cc/KvQmTswc/20260820-195746.jpg (https://postimg.cc/w7yK8F9n)

Those 3 white one moved convergence around. Looks like that's ok but geometry is a mess.


Geometry looks okay to me for a set like that. You have problems with horizontal convergence on the red, and the image is shifted to the left a little bit.

The tube is probably also a little bit beat. If you turn down the contrast knob, and the lines come together better, then it's more likely that the tube is just old and needs to be over-driven to achieve reasonable brightness. What happens is that the emissive material gets used up on the surface of the electron guns, and/or the phosphors on the inside of the tube start to fade, and then it doesn't get as bright anymore. You can turn up the contrast to make it brighter, but the system is only designed to operate at a certain voltage level. You could think of it in a way somewhat similar to how a home audio amplifier is only designed to amplify sound by the amount of watts it's rated at, except it's video amplifiers in this case. If you push an audio amplifier outside of it's operating range, the sound distorts. The same thing will happen if you push the contrast too high on a TV. Keep in mind that when the TV was new, it would have been much brighter when set at a lower contrast level, and so would not be as distorted.

I guess I've done bout all i can do. I think its pretty good for a 77 and its came a long way since I got it 2 weeks ago.

https://i.postimg.cc/NFwH2kg0/20260822-180654.jpg (https://postimg.cc/cgXHVYtq)

https://i.postimg.cc/2yFBQL6H/20260822-180818.jpg (https://postimg.cc/4HydZdpt)

I guess I've done bout all i can do. I think its pretty good for a 77 and its came a long way since I got it 2 weeks ago.

It looks pretty darn good for what it is.

I can't tell if it's just the exposure on your photo, but it looks a little too red/pink to my eyes. That can be tweaked with the tint knob on the front panel. Should be able to make the grey a little more grey, and Artemio's face should be more of a light tan skin tone.

The tint knob won't affect the grays. They could be adjusted by a slight tweak of the red G2.

The tint knob won't affect the grays. They could be adjusted by a slight tweak of the red G2.

I was thinking that after I left the comment. The tint will help the skin tones, but I guess the greys don't (or shouldn't) be affected by shifting the chroma. Whoops.