Ctc-12

[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.

[DaveWM]

well with the vert yoke unpluged it still scans about 1" high from the middle of the screen. Now can the purity/convergence cause a this? My next test will be to plug in a convergence yoke plug with the 100 ohm resistor.

[DaveWM]

was reading my RCA manual, says if AC line never drops below 120vac to go ahead and use the 128vac tap. So will be making that change. Also on vert setup, to use the lin control to fill out the screen as large as possible and the height to make as small as possible to just overscan, while still maintaining decent linearity. Had to do with vert convergence pulses.

[DaveWM]

new HOT got the screen voltage in line, dropped from (128v tap)150 to 137 with just a tube change. The new tap seems to be fine, did not seem to drop the overall B+ much but I feel better about it anyway.

I noticed a slightly blue glow in the 3a3 so maybe its getting a bit gassy, will sub in one of those next. cathode current still a bit high about 205ma, was about 220ma before the tap and tube change.

[DaveWM]

tried yet another 3a3, this time no blue glow at all. while I was at it I swapped a newer looking 6BK4 shunt (clear glass not as brown), HV went up so I adj back to about 24kv, holds steady from full to no brightness settings so I think its about done. I just need to bring it inside so I can watch it for a while and monitor the flyback heat. I would like to add a thermistor to the set even if I dont have the auto degausser setup just to save some stress on the switch. The CL90's that I have been using are only rated at 2 amps but there is a 3 amp one listed on mouser.

[DaveWM]

while futzing with the flyback, I noticed the sound seemed a bit weak, it starts nothing to weak, gets weaker to nothing (at around the loudness tap I presume) and then gets louder again, the tone control seems to have little effect as well. I am guessing something on one of the pots has shorted or one of the wires has pulled loose on the VC, I guess I will need to pull the chassis...again...oy