RCA CTC 120, weird tuner issue

[MRX37]

(TL DR the iron tuning slugs in both the audio and IF sections were crumbling into dust, throwing off the inductance, and throwing off the IF alignment)


Just when I think I’ve gotten out of the vintage TV collecting habit, I get pulled back in!

https://images2.imgbox.com/11/9a/mUfexVDx_o.jpg

It’s an RCA CTC 120 console set. It’s nothing special, except, it was just two houses from where I live, it’s in pretty good cosmetic condition, and it even still has the original power cord.

I first saw this TV while making a pit stop at home, and I said to myself “I don’t need it. I don’t need it. I don’t need it!”

I mean, I have an RCA Dimensia from November 1987, just before Thomson bought them. I don’t need a Mid-Tier Colortrak from 1983 that doesn’t even have A/V inputs!

So, I left it there, went back to work figuring a scrapper would come and get it and that would be the end of that.

I got home 3 hours later, and unfortunately it was still there, and still had the power cord.

As if to underscore that I was meant to save this TV, a scrapper pulled up right as I was wrestling it into the house.


"Grandma, you need to keep the TV on Channel 3! Use this remote to find Jeopardy!"

So I let it get up to ambient temperature and plugged it in, and unfortunately, it turned right on and soon displayed a picture. You see, I was looking for justification to put it back out on the curb. But it came right on and displayed snow on the screen.

The snow on the screen was rather dim, and had a green tint. And, oh, the Black Level and Picture controls were maxed out. Yes! That’s exactly what I had hoped for! The CRT might be shot! That means I can get rid of this thing! Can’t justify keeping it if it has a bad CRT!

No wait, early 80’s RCA CRT’s tend to hold up pretty well. At least check the bias controls on the back of the set.

Unfortunately, there was plenty of room left on the drive and bias controls, and even with them turned all the way down, there was still a visible, albeit dim picture on the screen. And with the brightness cranked up, there is no color bleeding. The focus and geometry all look pretty good.

Well, shoot. It looks like the CRT is okay. Were it 10 years ago I would probably have thrown it out anyway, but these days, finding an early 80’s RCA, in this good of cosmetic shape... I’d be a fool to throw it away. Good working CRT sets are starting to get rare and to have one this nice practically handed to me…

Well I guess I’m its caretaker now.

There is one problem. The tuner is acting weird.

This was testing with my HackRF using HackTV on Channel 2:
https://images2.imgbox.com/83/7d/mX1jmwwk_o.jpg

And this was Channel 3, same power output:
https://images2.imgbox.com/83/2d/dHvKTkmi_o.jpg


To verify that it wasn't an issue with my hackRF, I tried a known good DTV converter box:
https://images2.imgbox.com/40/d2/RVx4j2NY_o.jpg

I am certain it's an issue with the tuner, because testing on UHF produces a better picture, and I was able to (once) get a crystal clear black and white image with no distortion.


Additionally, despite the worn buttons in the front, I don't think this is a very high hour set. The screws in the back haven't been taken out often, or at all before I got to it:
https://images2.imgbox.com/2d/62/h7mPfGXl_o.jpg

And the inside is weirdly clean:
https://images2.imgbox.com/1d/76/WdGENv9y_o.jpg

I mean there's some dust, but not as much as I would expect for a 40 year old television that, supposedly, has seen high usage.

[zeno]

Pull & resolder the tuning modules. Especially at connectors. Watch
for cold grounds around shields. There are several 'lytic caps that
filter supply voltages. By the looks it may be on the @33 Volt tuning
supply. These tuners kept stakes on the table for us.

Zeno

[MRX37]

Okay so, bad solder connections likely in the tuner. That should be easy to fix.

Where would I find the capacitor(s) in that 33 volt tuning supply? I'm terrible with schematics. I do much better knowing where it physically is on the circuit board.

[MRX37]

Pretty sure it's not a bad solder connection in the tuner. I reflowed everything that looked questionable to me, and there is no change. And that ripple in the picture is telling me there's a bad capacitor somewhere.

While I was in there I took out that button pad, and the #3 button has been pressed so much that it broke off the plastic tab, which I find to be kind of funny. Stupid yet hilarious early 80's design. (WE MUST HAVE BUTTONS!)

So i fixed it with some HVAC tape:

[colortrakker]

Channel 3 button, huh? This set has probably seen a lot of video games.

[MRX37]

Originally Posted by colortrakker

Channel 3 button, huh? This set has probably seen a lot of video games.

Or, ya know, DTV converter boxes, cable boxes, etc...

[MRX37]

I don't think this TV has ever been serviced before:

It's still got the original straps holding the wiring in place, and holding the CRT neck board on.

I don't think the chassis has ever been out of this set.

I said this set was nothing special. I take that back. This thing survived 40 years of use, and still has life left in it. It didn't eat its flyback, or the HOT. It didn't overheat. It didn't even pop its fuse! That's pretty special.

[MRX37]

I have pulled and tested multiple capacitors. They all test fine. Good ESR, values within spec.
I have reflowed many questionable solder joints.
I have taken apart the tuner and reflowed any questionable solder joint I could find.

Zero change.

There is a horizontal ripple in the image when something like bright lettering is on the screen. Also, the audio sounds a little bit distorted.

I am not sure where to go from here, but I am wondering if i should start tweaking coils. Maybe 40 years of use caused the tuner IF to drift a bit?


Additionally, working on this TV is hard when you have a cat:

Human! Human I need you to stop everything you're doing and give me attention!!

Some help on what to try next would be appreciated. I can post video of how the set is acting if it will help.

[vol.2]

Originally Posted by MRX37

Some help on what to try next would be appreciated. I can post video of how the set is acting if it will help.

Zeno is much better tech than I, but it looks like horizontal sync problems to me. Either caused by the tuner being dirty or something else. I remember seeing that kind of symptom and getting rid of it by grinding the tuning knob back and forth a bunch with deoxit in there.

I'm assuming you tried that and it didn't help though.

I guess the next step if no one else has any "known faults" to try, and you poked around for anything obvious already (caps with guts spewed or burnt spots on the PCB or reflowed solder), then the next step is to start checking voltages and hope you find a problem that way.

Problem is that I don't know that a sync problem would always manifest as a voltage issue. It's possible that something is just out of alignment. You never know if someone else got there first and started tweaking stuff. To do an IF alignment, I think you probably need a signal generator that can do a carrier wave or whathaveyou. I have never been able to do that because I lack that equipment. Perhaps there is some way to fake it with a normal signal generator, but idk.

If you have the schematics, you can at least check the main power supplies just to do a sanity check. I've caught a lot of BS that way. Otherwise if you don't have the schematic (better yet the SM), not sure how you'd do anything else beyond poking around.

[MRX37]

Originally Posted by vol.2

Zeno is much better tech than I, but it looks like horizontal sync problems to me. Either caused by the tuner being dirty or something else. I remember seeing that kind of symptom and getting rid of it by grinding the tuning knob back and forth a bunch with deoxit in there.

Uhhh... This is the 80's. WE MUST HAVE BUTTONS!

Yeah this TV has one of those early digital tuners. No tuning knob to clean. And, as surprising as it sounds, I don't think *anyone* was in the set before me.

I don't have service data and this set's not worth me buying a SAMS just for it. I kinda gave up on TV repair years ago. I'm only trying to fix this one because it practically fell into my lap.

Now if I knew what voltages to expect yes I'd check those.

UHF is not as affected, and with a good strong signal on a UHF channel, i can get a good picture. That tells me I can rule out the deflection circuits.

But it's really looking like alignment drift. Because I can see those squiggly lines when the sound bleeds into the video.


EDIT: Did a search here and found a couple posts about bad filter capacitors causing a "twisted" picture. So I pulled the filter cap and tested the sections.

Filter cap tests fine. The 30uf section tests at 41uf which is a bit high, but the ESR tests fine. The 600uf section is right on point.

[damen]

There are two trim pot controls located in the top left corner of the chassis. They are labeled "AFT balance", mark where they are and see if adjusting them makes any difference, if not, set them back where they were. If the controls don't help, aligning the AFT crossover coil may help. It should be labeled on top of the metal shield L304 on the left side. To adjust the coil, with the set on and tuned to a channel, turn the coil slightly in one direction, less than one turn, then interrupt the signal by switching to 04, the back to 03. Each time the coil is turned the set needs to fine tune itself that's why the signal must be interrupted. Also check and clean the sharpness control on the back apron of the chassis. The sound may be cleared up by aligning coil L201, it's just in front of the audio IC where the speaker wires connect. This coil uses a different alignment tool than the AFT coil one. There should be a paper chart in the cabinet that show these parts locations.

[MRX37]

Interesting. I noted the sharpness control doesn't seem to do much. I didn't mention it because the picture looks fine.

I have a set of ceramic screwdrivers coming. When i get them I'll start tweaking coils.

[vol.2]

Originally Posted by MRX37

I don't have service data and this set's not worth me buying a SAMS just for it. I kinda gave up on TV repair years ago. I'm only trying to fix this one because it practically fell into my lap.

woof. Honestly I just get a manual whatever I can if I'm doing a repair because it always saves so much time, and 20 bucks ain't much time these days.

There's no reason to fight it. You fix TVs again now. All is right with the universe.

[MRX37]

Originally Posted by damen

There are two trim pot controls located in the top left corner of the chassis. They are labeled "AFT balance", mark where they are and see if adjusting them makes any difference, if not, set them back where they were. If the controls don't help, aligning the AFT crossover coil may help. It should be labeled on top of the metal shield L304 on the left side. To adjust the coil, with the set on and tuned to a channel, turn the coil slightly in one direction, less than one turn, then interrupt the signal by switching to 04, the back to 03. Each time the coil is turned the set needs to fine tune itself that's why the signal must be interrupted. Also check and clean the sharpness control on the back apron of the chassis. The sound may be cleared up by aligning coil L201, it's just in front of the audio IC where the speaker wires connect. This coil uses a different alignment tool than the AFT coil one. There should be a paper chart in the cabinet that show these parts locations.

adjusting one of the AFT balance trim pots helped a little bit.

Adjusting L304 really affected things.

I wish I could tell you more, but the ceramic bits I ordered are too #$%^&* short to properly reach the slug... so i'm waiting on a set of proper coil alignment screwdrivers.

Also sprayed deoxit into the sharpness control.

[MRX37]

Are
You
Kidding
Me

The set of plastic alignment screwdrivers showed up today. Two of the fit L304.

L304 stripped one, and broke the tip off the other. The plastic tip is now jammed in L304.

This was ***AFTER*** using Deoxit to help free up the coil.

I am about furious enough to do a radiotvnut and EOL this "thang", but at the same time, I am not going to be beaten by a freaking IF coil.

So I'm probably going to desolder it one day when I have time and try to free it up.