Ok. Let’s try this again…RCA 9TC240 Alignment

[Chris K]

Wow. That’s so different and really helpful. I’ll give it a try. Not exactly free as I thought this morning myself! Sitting in the car in a he parking lot outside the salon while my wife gets her hair done! I’ll let cha know later today.

[Chris K]

Originally Posted by Penthode

I checked step 6 and see the problem. The instruction manual has an error. The table gives an incorrect connection of the VTVM to the junction of L104 and R126. You need to measure across R119 with the case of the VTVM at -120vdc.

Please explain because you were talking as if the VTVM was faulty.

I'm going to get set up shortly to start with step 6 in the alignment again as per your instructions but I'm a bit concerned whether or not we are on the same page...literally on the same page and chassis. I don't see a mention of L104 and R126 anywhere in the Riders documentation I'm using. I know there was some confusion before as to what chassis this thread was about so I just want to clarify with a few words and pictures. My chassis is the KCS28B in the 9TC240 model and below are pictures of the alignment instructions and the table of alignment steps.

[Penthode]

Mine was a 1948 publication. They fixed it in yours.

Makes no difference in my suggested procedure. I think mine better as it eliminates the DC offset to the meter and you can measure an actual signal and not just carrier amplitude.

[Chris K]

I'll check it out just for fun. I have the first 4 volumes. Gonna get on the adjustment tonight. Will I get the 1KHz tone through the speaker and will monitoring it during the tuning process provide any additional guidance?

[Penthode]

You won't hear the tone or it will be pretty weak. First it is AM. Second the 19.75MHz and 27.25MHz traps are pretty remote from the 21.25MHz sound IF.
You could see it on a scope. But just be sure you detect the tone on the VTVM by varying slightly the RF level. When you tune for the notch, the null should appear pretty obvious.

[Penthode]

Seems this thread has gone dead! I wonder what happened?

[Chris K]

Just haven't had a chance to work on it. Life happened. It's not forgotten or given up on...I just haven't had any time over the last 10 days. Fear not!!!

[Chris K]

Hi all. Lots going on here but that's life. All the traps and transformers have been nulled and peaked according to the new testing scenario laid out by Penthode. I'm now at the point of adjusting T-1 and T-101 with a sweep from 20-30 mc symmetrically around 25mc. It's kinda a mess. Amplitude is low and it doesn't look anything like the two peak response curve in figure 15. I'll post some pictures shortly. I hate to start thoughts of feeding composite video in this but I'm starting to consider that option. I have checked the multiburst bar sweep and the resolution isn't much better than it was when I started all of this. Maybe this TV was too much too soon for me. I did get further than I ever have in the past and I've learned so much about how these circuits work. Right now, the challenges of this are blocking work on other projects I want to get into. Other than holes in the chassis for the RCA plugs, there's nothing irreversible about cutting in with a signal at the video and audio amplifier section. I'm willing to give this process one more shot...start to finish. I mean all the way back to de-tuning T-113 in step 1. Despite Penthode's helpful suggestion with the alternate method for tuning of the video section and being pretty confident in getting the correct responses on the VTVM, there's still no change in the quality of the picture and, as I said, the T-1 T-101 tuning step is a mess on the scope despite hooking up the 330ohm resistor shunts correctly and feeding in a sweep signal at a number of different amplitudes correctly. Like I said, I'll give it one more comprehensive shot but if it fails, well, I have some decisions to make. Thanks all.

[Penthode]

Show some pictures of the response with markers and we will set you straight. Forget about doing it any other way. Feeding in composite video and trying to adjust to to that will not work. You are getting there and all you need is patience and perseverance. And the results when done right will amaze you because this set delivers superb pictures.

The signal level will be low because of the shunts across the IF stages. You must turn the RF level up. The main thing is you must ensure is when varying the RF level, there should be no change to the shape of the RF response curve. Only the amplitude of the response curve will change. Make sure the ground connections are good. And show a picture of the sweeper generator panel so we may see the settings.

Patience!

[bandersen]

I believe he is considering injecting composite video directly into the video amp and bypassing the IF entirely.

[Penthode]

Thanks. I only realized that after the post.

Feeding in composite video is crummy on this set because you will lose the DC component unless you create a clamp circuit at -120 volts. Think about it. It is messy.

[Alex KL-1]

Originally Posted by Chris K

Hi all. Lots going on here but that's life. All the traps and transformers have been nulled and peaked according to the new testing scenario laid out by Penthode. I'm now at the point of adjusting T-1 and T-101 with a sweep from 20-30 mc symmetrically around 25mc. It's kinda a mess. Amplitude is low and it doesn't look anything like the two peak response curve in figure 15. I'll post some pictures shortly. I hate to start thoughts of feeding composite video in this but I'm starting to consider that option. I have checked the multiburst bar sweep and the resolution isn't much better than it was when I started all of this. Maybe this TV was too much too soon for me. I did get further than I ever have in the past and I've learned so much about how these circuits work. Right now, the challenges of this are blocking work on other projects I want to get into. Other than holes in the chassis for the RCA plugs, there's nothing irreversible about cutting in with a signal at the video and audio amplifier section. I'm willing to give this process one more shot...start to finish. I mean all the way back to de-tuning T-113 in step 1. Despite Penthode's helpful suggestion with the alternate method for tuning of the video section and being pretty confident in getting the correct responses on the VTVM, there's still no change in the quality of the picture and, as I said, the T-1 T-101 tuning step is a mess on the scope despite hooking up the 330ohm resistor shunts correctly and feeding in a sweep signal at a number of different amplitudes correctly. Like I said, I'll give it one more comprehensive shot but if it fails, well, I have some decisions to make. Thanks all.

Perhaps the best thing is indeed to make a non-invasive direct video feed (without opening holes in cabinet or chassis), playing with that, and other things. Then, some time ahead, you can return to this issue with "not loaded mind" ("not tired mind" (I forget what the term for that in English).
Sometimes for me, for example, heavy projects (for the mind) I end years after the starting, after some big pause.

[Penthode]

As I said a direct video feed will lose the DC component of the video.

Honestly, the problem I see here is proceeding with the alignment without understanding how the set works. The alignment although long is being wrongly interpreted. I see the same problem attempting to introduce composite video feed.

Now that the correct test equipment is being applied, the alignment will be quite straight forward.

Let us see what the problem is here. I suspect it is a trivial mistake of adjusting equipment.

[Chris K]

It could be a trivial thing. I injected a composite signal directly into my RCA 721 with no issue and ended up with a high quality picture...an order of magnitude better than through the tuner.
I do have a pretty good idea of how the signal is going through the IF and being filtered and modified but there are certainly aspects of getting a decent picture I don't understand.
I'm getting 3 KCS28 parts chassis in about a week plus a NOS 10BP4. I definitely want to replace the brightness control and I want to proceed carefully knowing I have a ready supply of replacement parts. Two of the traps I got from Bob are like most of these...stuck slugs that need a bit of mineral spirits to get them working but even with lubrication, they don't turn all that easily. The other issue with the slugs is a lack of robustness in that the iron slugs are solid but the threads, and I use that term lightly, in the coil tube are very susceptible to damage. They're not really threads but more like cuts in the inside walls of the tube every 90 degrees and it doesn't take much to strip them out. I can see why manufacturers quickly went to sticking a threaded rod in the slugs and made it ride up and down in a metal channel in the top of the can.

[Penthode]

It is not as simple inserting composite video in this set compared to the 721. I have a 721 and the picture is excellent through the tuner and IF. The set you are working on is better but if all you are interested in is getting a picture on the screen, yeah that will work.