Rca CTC-25 overview and help

[Electronic M]

The switch positions should be fairly obvious.. the potentiometer positions that you seem to be asking about vary with CRT health, signal conditions, and opperational health of the chassis.

Assuming you have the right HV voltage, focus voltage and the right boost voltage (if not focus on getting those right before expecting light on screen) then crank the brightness clockwise with contrast Midway and color fully counterclockwise and look for light...If none flip to service position on service switch. If still nothing then while watching the screen (in a mirror if needed) turn up one screen/G2 control till it gives light or you hit its mechanical limit...if you hit the limit reset to about where you started and try it on a different color screen. If still nothing after all screens tried look for a subbrightness control and crank that. If still nothing check cathode and geid voltages against the schematic.

Assuming you get light and have messed with G2 here's how to set G2 on a working set...turn brightness to min flip service switch feed set blank signal, turn red g2 for faint red line, then turn green g2 to make line yellow, then adjust blue to get white...if a color.is too weak turn up subbrightness or if none exists brightness and start again... that should make blacks black...if whites are funny colored adjust color drive controls.

[ZenithNut]

Originally Posted by Electronic M

The switch positions should be fairly obvious.. the potentiometer positions that you seem to be asking about vary with CRT health, signal conditions, and opperational health of the chassis.

Assuming you have the right HV voltage, focus voltage and the right boost voltage (if not focus on getting those right before expecting light on screen) then crank the brightness clockwise with contrast Midway and color fully counterclockwise and look for light...If none flip to service position on service switch. If still nothing then while watching the screen (in a mirror if needed) turn up one screen/G2 control till it gives light or you hit its mechanical limit...if you hit the limit reset to about where you started and try it on a different color screen. If still nothing after all screens tried look for a subbrightness control and crank that. If still nothing check cathode and geid voltages against the schematic.

Assuming you get light and have messed with G2 here's how to set G2 on a working set...turn brightness to min flip service switch feed set blank signal, turn red g2 for faint red line, then turn green g2 to make line yellow, then adjust blue to get white...if a color.is too weak turn up subbrightness or if none exists brightness and start again... that should make blacks black...if whites are funny colored adjust color drive controls.

I hooked up the rf output rca jack to the tuner and fired it up. Same thing. So I turned it off and took off the top of the fly cage and turned it on. Visible corona cloud around the cup of the fly back and the g output cathode current leveled at 200ma. I then saw a little bright flash in the 2av2. So i shut it off. So theres definitely hv. But why would the cathode current jump with the hv rectifier connected? I did have to resolder the 2nd anode connection on the base of the hv rectifier. I know the crt isnt shorted

[old_coot88]

Originally Posted by Electronic M

...if a color is too weak turn up subbrightness or if none exists brightness and start again...

Doesn't the '25 have a Kine Bias switch? If so, it might be dirty. Try cycling it a few times with a shot of cleaner.

[Electronic M]

Originally Posted by old_coot88

Doesn't the '25 have a Kine Bias switch? If so, it might be dirty. Try cycling it a few times with a shot of cleaner.

Could be... its been about 2 years since I last saw the inside/back of one...

[ZenithNut]

Originally Posted by old_coot88

Doesn't the '25 have a Kine Bias switch? If so, it might be dirty. Try cycling it a few times with a shot of cleaner.

Yes it does. The thing is it had everything working when I brought it home. Niw that ive done work on it i have this to figure out.

I replaced the boost diode with a 1n4007 and this other diode labled ge gecr-2 with a 1n5408. I also replaced a few small value e caps here and there.

Last night i was wondering why the h output current would go up 50+ma with the hv rectifier in circuit so i swapped the 6bk4 shunt regulator with a 6el4 and a fat (i wanna say 10 watt) 600 ohm resistor under the shunt reg started going up in flame. The leads were green anx corroded looking. So now i have that to clean up.

I do know theres hv at the fly output though.