My CTC-16XL Project. - Page 11 - Videokarma.org TV - Video

Yamamaya42 · #1 05-01-2019, 11:06 PM

i'm going to have to go over the whole PCB now and check all the res they put in now, knowing this, I should never have assumed they did it right when I saw that the Resistors had been changed T_T.

Yamamaya42 · #2 05-02-2019, 07:29 PM

Hot damn!

did a quick change of r145 to the right value, and cathode voltage of Burst amp is right on target! 41v.

Will go over the PCB this weekend for other wrong resistors, and attempt color AFC setup again!

old_tv_nut · #3 05-02-2019, 08:55 PM

Woohoo! Fortunately you found it. Unfortunately you will have to be suspicious of everything the previous guy touched.

Rocket · #4 05-02-2019, 09:20 PM

Awesome!!
Cant wait to see this set running : D

Sucks the last guy screwed up so much on this set and will have to be suspicious of everything. However it will be pretty rewarding when you get this thing running

Yamamaya42 · #5 05-04-2019, 01:08 PM

Latest status
Still unable to to preform Color AFC Setup.

Only able to see barber pole effect. ( still may be IF related, unknown )
BW pic is very stable.
Cathode v on burst amp is now at 40v, where it should be, but seeing a 10v saw tooth wave there, not sure if this is normal.

Not finished going over PCB for other errors yet..

evidence that L24 ( bandpass coil ) may have been replaced.

STILL getting no scopeable video on the far ( badpass ) side of C22, it also looks to have been replaced. Removing v17, killer / chroma bandpass tube makes no change in this, but lifting the far side of the cap does.
This situation was first spotted years ago when I got the set.

Will have to try and dig deeper ( find other errors ) to work out why it's dong this,
From what I understand, and how this all works, if NOTHING is getting past C22, or its getting distorted somehow, there is nothing for the Burst amp and bandpass to work with, and thus the color osc can't lock on and so on...

I should see SOMETHING on both sides of C22, right?

Electronic M · #6 05-04-2019, 06:02 PM

If the chroma osc is too far off freq it won't sync even with ideal sync input/synch circuit performance.

Sync or not you first need to get it to the point where you can tune the osc to not have many barber Pole lines but what looks like continuous to tint drift... once you get that if there's any life in the chroma sync it should be able to lock.

Yamamaya42 · #7 05-04-2019, 08:14 PM

Quote:

Originally Posted by Electronic M

If the chroma osc is too far off freq it won't sync even with ideal sync input/synch circuit performance.

Sync or not you first need to get it to the point where you can tune the osc to not have many barber Pole lines but what looks like continuous to tint drift... once you get that if there's any life in the chroma sync it should be able to lock.

but i'm not sure I'm getting anything for it to lock onto.
I'm seeing nothing at the bandpass coil even wit the tube removed ( same tube has the color killer )
there are no pules at all v23 chroma phase detect.

what should i be seeing at point 80 ( v17 removed )? I'm seeing nothing but noise, no video, the overpowering horz pulse that was there is gone, but, no video, so i suspect there is an error someplace that i have not found yet .

old_tv_nut · #8 05-04-2019, 09:43 PM

Sawtooth on cathode is normal.

Back of envelope without using exponentials: Average current is 1 ma (40v/39kohms). This is supplied in a narrow pulse of, say 2.5 microseconds, or 1/20 of the horizontal rate. So, the peak current is 20 ma for 2.5 microseconds, = 50 nanocoulombs. This causes a rise of 5 volts on 10 nF C98.

Yamamaya42 · #9 05-06-2019, 03:11 PM

Copied from “no color on CTC-16” thread, almost exactly like mine.

Posted by Old TV Nut.
So, go back to grounding point E. This should defeat the color killer and let the bandpass amp conduct. Turn the color control all the way up and see if you see any color.

As far as using the scope, set the scope sweep rate to horizontal sweep rate (about 10 microseconds per division). For starters, set the vertical sensitivity to 10 volts per division (or 1 volt if you have a 10X probe) and check for presence of all the waveforms shown in the SAMS schematic for the chroma sync phase detector and color killer, plus the chroma bandpass. Set the vertical to higher gain to view the smaller waveforms that are marked about 10 or 12 volts peak to peak.

Do you have a color bar test pattern to use, or are you using some program video? The chroma waveform on pin 3 of coil A14 will generally not be as big and obvious with program material as with a test pattern, but you should be able to see it come and go when the color killer operates.

This is most likely the source of my problems now, As when Point E is grounded, I get absolutely nothing at g1 of u17 ,even at 200mv, I just see noise , nor is there any signals at chroma phase detector,
but the ref Osc is running, I can see that, not sure what freq.

I do see the horz pulse at g1 of the burst amp, but it still never changes with the video on screen, even though that r145 is correct.
What I don't know (or understand yet ) is something so messed up in this circuit that won't allow video into it through c22 (from 1st video amp) for any of the color to work correctly ? Could IF section be so out of wack that it is not letting any color through for the circuit to work with? A combo of both perhaps?

Yamamaya42 · #10 05-08-2019, 08:53 PM

OK, update...
After spending nearly 2 hours checking every resistor that was replaced on the color PCB, I found one more that was wrong, R170 has a 10k in it where it should be 27k ( so says SAMS ).
Other than a lot of crappy lead shaping and sloppy solder work, the other resistors are OK. ( I have a very critical eye for lead shaping and solder form, this comes from my many years in the industrial electronics field ) .
There are a few caps that still look old, that I will most likely change this weekend.
However, I really doubt that this will fix the problems, for I'm pretty sure that the putz who did this messed with the IF section and I have no real way to align it.

So once I am done checking the color PCB, I will try again to tap in video at the 1st video amp, this time lift up one end of l9, and try color setup with external video, this MAY cause a problem because composite video is 1v PtP and the wave shown at that point is 3.5, I may have to build a small video amp, or it may not care.

Yamamaya42 · #11 05-11-2019, 01:10 AM

I have pretty much confirmed it now, this putz has made a mess of this set, and it will be very hard to set right.
The IF is messed up and wont pass color, any that does get through, is so weak that the color circuits cant process it. Any color seen via the the tuner is so faint ( seen as barber-poling) you can hardily see it on the screen.
I have found and fixed 4 mistakes on the color PCB , so I can only assume that when they first tried to fix this and did not notice/ check their work they then turned their attention to the IF pcb , and made things worse, gave up, then donated this TV to the place where I found it .

When I try to insert direct video at the 1st amp, I get a MUCH stronger color signal to the color circuits and very pronounced color barber-poling on the screen, but I'm still unable to do the color afc setup that way because the sync/ afc is unstable, this is most likely due to that I'm feeding feeding in composite video ( 1v p2p) at a point where it should be 3.5.
dvd input
https://imgur.com/IMh054m

So now I have few options, try to find a way to get the IF un-messed up ( aligned ) so the color setup can be done correctly, or try a video amp and hope it stabilizes things enough to let me do color setup.

Yamamaya42 · #12 05-11-2019, 11:12 AM

https://imgur.com/m0IePGv
With 3rd video IF removed & composite taped in to 1st video amp. ( lead clipped to TP1 @ L9 )
I have checked resistors on the IF and found very few out of tolerance, and my chances of finding anyone local with the equipment and knowledge to align it is pretty much zero, my only chance is to try to build the video amp for it.
You can see the stark difference black levels with input via tuner in the last post and this one, so it is very much needed.

Electronic M · #13 05-11-2019, 11:34 AM

Quote:

Originally Posted by Yamamaya42

https://imgur.com/m0IePGv
With 3rd video IF removed & composite taped in to 1st video amp. ( lead clipped to TP1 @ L9 )
I have checked resistors on the IF and found very few out of tolerance, and my chances of finding anyone local with the equipment and knowledge to align it is pretty much zero, my only chance is to try to build the video amp for it.
You can see the stark difference black levels with input via tuner in the last post and this one, so it is very much needed.

That screen cap has enough color info that you should be easily able to achieve synchronized color with adjustment of the chroma osc/osc control.

old_tv_nut · #14 05-11-2019, 11:36 AM

You may not be able to lock the color at this point, but you could try the procedure to the point where you have oscillator frequency adjustment zero-beating with incoming chroma.

Yamamaya42 · #15 05-11-2019, 11:51 AM

Quote:

Originally Posted by old_tv_nut

You may not be able to lock the color at this point, but you could try the procedure to the point where you have oscillator frequency adjustment zero-beating with incoming chroma.

I tried, w/o much success, as you can see, I don't even have a strong enough video input for the blanking amp to work T_T.
But, after an hour searching online, I think I just may have found what I need!

http://www.next.gr/uploads/113/Simpl...it-diagram.png

will it work? only one way to find out!

edit
I'm also looking at the lm359 op amp option.