[ARC Tech-109]

simple things first, check the color killer control? Turn it to the left on a blank station and the screen should look like it has colored confetti all over. No change from the control? Check the phase det diodes CR701 and chroma sync diodes CR702 (T940 schematic) the nominal voltage should be about -2.0V on the grid of the triode section of the killer/burst amp 6MQ8/6KE8. The diodes are germanium 1N34's and are known to die without warning. I pulled mine and wired in a pair of 6AL5 twin diodes on wafer sockets. Same with the horiz AFC diode pack. If the burst amp isn't getting a signal it won't feed the color killer and that will keep the bandpass amp grid-1 cutoff so make sure it's opening up the bandpass.

Check for chroma subcarrier coming into the chroma take-off coil, it's fed from the 1st video amp plate via 18pf ceramic cap (C742). Look at the the output of the bandpass amp pin-6 of the 6HG8 V707a. Signal present then check the output of the 3.58 osc, you can pick up the output on the X-Z demod 6MK8 at pin-9 and it should have greater than 15V P-P. Signal present? Check to see if the auto color circuit or the switch is cutting off the chroma subcarrier. In my T940 its broken away to feed the TAC just before the color control and the total auto color circuit is switched in & out by a slide switch on the back, regardless of the setting the subcarrier passes thru the board then down to the main color control R402 before feeding G-1 pin-7 of the 6MK8 demod. I completely bypassed my TAC auto color board as it never completely shut off. That board was too far advanced for the time and proved to be a big pain in the back side, germanium diodes and transistors are not heat tolerant.

The best advice I can give here is to follow the signals on the schematic, the big challenge I had with my T940 was drifty carbon comp resistors. Cold they were fine but would drift up with heat causing all kinds of weird problems later in life. At some point I will be replacing them all on the chroma/luma and IF boards, the sweep board got all new 5% films in 2005 to address horiz & vert stability problems.

There are a number of those mylar type capacitors that I've had trouble with over the years. They are as follows in my T940:
C715 0.1uf 400V DC filter on leg of 6DT6 audio det from boost B+ (low distorted audio)
C721 0.033uf 100V AGC line to tuner
C722 0.1uf 100V IF AGC drive (washed out video)
C732 0.047uf 200V killer output bypass cap.
C749 0.1uf 100V 3.58MHz osc control R/C in series with R764
C773 0.047uf 200V. XZ demod screen bypass
Normally Mylar is like a lifetime capacitor but being baked over half a century they will die. I replaced them all with orange drops from AES.

Seeing the glow in your set makes me want to pull mine out of storage, unfortunaly it would take up a large chunk of my apartment being a lowboy console. Someday I will get my sanity in check and dump my plastic fantastic sets for the AstroSonic.