RCA CTC-11 Chroma Alignment Issues

[TonyP]

My first question is, where is the mixer grid test point on the tuner? Ive found two test points. one goes to pin 2, and another to pin 3 of the 6EA8.

MY first attempt was to use the Sencore SM 158. I biased off everything the RCA service manual says. I connected everything like the RCA service anual says. The first step is to inject a signal directly into the bandpass amp to pre set the bandpass xformer. i got no response curve on the scope. Then i tried connecting the RF cable to the antenna terminals. Still no response curve. I used the Sencore supplied detector clipped to the grid of the 12AZ7 demodulator.

Ok. Decided to break out the RCA Gear. I have the WO-91A scope. WR-69A seep, and I used my Precision E-200c for a marker gen. I also used the WG-304A RF modulator and the WR-295B video marker box.

SO, first step is to use the sweep gen and the marker box to inject a signal directly into the bandpass amp. Video detector probe on the grid of the 12AZ7 demodulator. ok. got a response curve on the scope.

THen, i go and change the setup to inject a signal into the mixer grid, set everything up for VSM alignment, dector probe on the 12aZ7 grid. no repsonse curve at all.

I did not make the video detector probe like is shown in the RCA service notes. i am using the dector probe that came with the BK 415. My other thought is my front end of the tv is dead, but it is a working tv, unsless i did something when i set up the bias voltages.

IF you go to section 6 of the RCA TV Home Study Course, it actually has the CTC-11 alignment instructions and a schematic, So, i used this as my guide. https://worldradiohistory.com/Archiv...ourse-1966.pdf

I am attempting alignment only becasue when i went to check and tweak the burst phase, i tweaked the choma bandpass transformer by mistake. so, i wanted to recheck to see if it was off.

[old_tv_nut]

If you only touched the chroma bandpass, don't bother with the IF/tuner. You can always play with it later as a learning exercise, but if it ain't broke, don't fix it.

Is there something wrong with the picture that tempts you to do the tuner and IF?

[TonyP]

Are you saying skip using the VSM method to get an overall response curve? All the books Im reading is saying use the VSM to get an overall response curve from the tuner to the output of the bandpass amp. even sencores method is this way. well, i wasnt going to tweak anything in the IF section, but the fact I cant get a response curve at all is something I want to figure out. Something wrong with the tv, or something wrong with my gear, or my set up? I did manage to get a curve when direct injected into the bandpass amp, as per Step 1 of the Rca service manual. But following the rest of the instructions gives me nothing. I hope i didnt short and burn something out when connecting up the bias voltages.

[old_tv_nut]

Originally Posted by TonyP

... I hope i didnt short and burn something out when connecting up the bias voltages.

I don't think that's very likely. (Nothing smoked, right?). Disconnect your test gear and check that you can get normal reception, that will tell you if anything is dead.

Once you know it's basically working:

Double check all the connections after leaving it alone for a while. Sometimes a mistake is right in front of you but requires fresh eyes to find it.

RF/IF gain is very sensitive to the AGC/bias voltage. You may need to adjust the input signal level through a wide range to get something through, and if that doesn't work, adjust the applied AGC/bias voltage.

[old_tv_nut]

Regarding skipping the over-all chroma response from front end all the way through:
Since you didn't touch the RF and IF, you can pretty well assume they are OK, and only the chroma bandpass that was touched needs resetting. When the chroma bandpass itself looks OK, just look at a picture to see if there's anything obviously wrong. If not, then the RF and IF alignment is only a training exercise.

[TonyP]

Since I cant get an over response curve, i was going to do just that. Get the bandpass set as best i can. Still want to figure out why i cant get the over all curve to show. I got my chroma curve as close as it shows in the service manual. It shows the markers actually juat starting on the outside downward slope of the curve. My markers are just over the hump, going toward the inside slope, closer to where the 3.5 mhz marker is. The 4.5 mhz and 2 mhz markers are in the general location shown on the curve in the service notes.

[old_tv_nut]

Are you sure the applied AGC bias is the right polarity? I seem to recall a SAMS for one set that had it backwards.

[TonyP]

Im using the rca service manual instructions. Did you see i linked to an rca home study course? In volume 6, there is a whole lesson built around ctc 11 alignment. And im following it to the letter, even using rca gear, except im using a regular signal generator in place of the rca marker generator. The other deviation is i did not build the video detector that rca specified. Im using the demodulator probe that came with the BK 415. Using the RCA chroma alignment instructions, i can perform step 1 ok. Its steps 2 and 3 i get no response curve for. My only guess is some stage ahead of the bandpass amp is not working. I have the chassis on the bench, not connected to the tv, horizontal disabled. Im gonna have to do some troubleshooting. Maybe conect a dvd player and see scope the video amp to see if i got signal. If so, then one of the color sections must have quit. Or the front end quit, since i get nothing trying to inject signal at tuner.

[old_tv_nut]

Since you aren't hooked up to see a picture, everything you just wrote makes sense. Good luck.

[dtvmcdonald]

In some TVs, color won't work without horizontal because of a keyed color killer.
In early RCAs this biases off the color amp. I'm not sure about later ones. Look
at the bias on the chroma amp grid. You could make it work using a bias box or battery to override the color killer.

On my CT-100 I adjusted color with the yoke out of the set and connected up
so horizonatal worked.

[Tim Tress]

Try to get the luminance channel working first. Inject a signal into the tuner from a DVD player or Analyst, and scope the output of the video detector. With the horizontal section disabled, the AGC circuit isn't going to work, without a keying pulse; you'll have to use a bias box instead. If you have no video at the detector, the problem is "upstream", in the IF strip or tuner.

[TonyP]

Thate my problem. Injecting the signal at the tuner IS NOT giving me a response pattern on the scope. If I inject it directly into the bandpass amp, I DO get a response curve on the scope. And i am using the directions in the RCA Factory Service Manual, so external bias is being used. This tv was working, so either something in my set up isny working, or maybe i killed something setting up the equipment. Yes, i need to follow a signal from the video amp back.

[TonyP]

Anyone have an idea why I cannot see the overall chroma response curve? I am following the direction in the RCA service manual and even using RCA gear. Only deviations are a regular signal signal generator in leiu of the rca 99a marker generator, and using a generic scope demodulator probe over the video detector RCA says to make. Horizontal is disabled, but it also says to disable in the instructions, and im following them to the letter with the same bias voltages and points specified.

[old_tv_nut]

You don't say if you have tried any of the signal tracing suggestions to find out what is dead. No way to guess if you don't do more diagnostics.

[TonyP]

The tv is not dead. It is connected back up to the crt and its happily working. Horizontal is diabled. Even with biasing off what they say to bias off, nothing. Something in my setup is not working. Im following the directions to the letter. Even tried another brand of sweep generator. Same results. No response curve seen. I aligned just the chroma bandpass amp by itself, like step one says. I just want to get the total response curve to see if the chroma take off coil needs a tweak, and for the heck of just doing it. I will not touch the IF at all. I posted a link to the RCA color tv home study course. Following the instructions in there to the letter. Maybe some old hats could look them over. Possible there is a mistake in the directiins that only an experienced person could catch.