Ctc-12

[IsthmusTV]

Looking good, Dave! And it sure didn't take you long to get it up and running. Usually, no fly would be a show stopper. Congratulations on another roundie saved!

-Clark

[DaveWM]

this one had no problems at all but for the missing fly, was lucky I had an extra that was a bolt in replacement. the only other thing I plan to do is add a single term strip to the chassis and bring out the cathode from the HOT to it. that will make checking the HOT current easy. I would like to add a 'HI-LO' ac voltage switch but that may be taking things a bit far. I just don't get why they went thru the trouble of tapping the primary of the PT and then did not bother to make it easy to switch. In later chassis like the 16 i know there was at least a term strip that could be accessed from the top of the chassis to move a jumper around. I could mount a two lug term strip one with the 117 and one with the 128 then have a jumper to select, but the idea of the AC up on the top of the chassis scares me a bit.

[DaveWM]

drilled a small hole in the chassis near the back, attached a small spade connector, then used a jumper from the HOT to connect it. I clipped the orig 3-6 ground wire but just bent it down out of the way. Now checking HOT current will be very easy.

[DaveWM]

well at full line voltage of about 125vac I get about 220ma min, at 115vac its about 200ma, so I think I will look into using that tap. I will also check the HOT grid bias to make sure that is correct. Something that bothered me was when checking the 270v test point on the back of the chroma board, I came up with 250v and that was at full line voltage. Since the biggest draw on current is prob the sweep circuits, its just another reason to confirm that all is well in the horz out.

[DaveWM]

interesting clue, screen voltage seems high at about 165v vs 135v a vaguely remember fighting an odd high current problem before. The clue is the vert center pot is at one extreme end and the setup line is just to the middle, maybe not quite all the way. Letter box is not even either. The screen voltage is tied into this 10 ohm pot. I am going to check it to make sure it did not open up on one end. It does move the vert but just not enough.

[DaveWM]

well the vert cent pot was open on one side, so that should help with the centering and maybe the excessive screen voltage on the HOT.

I did notice that some work had been done there before. one of the ends of the pot (the one with two wires and a resistor on it) still had the remnants of a pot leg soldered on, like they did not bother to undo the the pot before, just cut off the leg that was there and solder it on to the new pot.

My guess is these vert centering pots were a common failure point.

[DaveWM]

very odd, the pic is still too high on the screen, I tried reversing the vert yoke leads, again too high on the screen (had to go the the other extreme end of the vert cent to try and center the upside down pic, I am not 100% sure I got that right it got a bit confusing, next time I will just center the pot and see what happens).

I am going to try just unplugging the vert yoke and see where the center line falls (yes brightness will be turned down).

I don't recall if this is normal but in the service setup mode the cent line can be moved by the vert cent pot. At the extreme end its nearly centered but not quite.