|
Okay, here's a slight puzzler. The horizontal oscillator frequency is still too low, and can't get it in range with the horiz osc coil. Attached is the relevant section of the schematic. As you can see, the osc frequency is primarily determined by L118 (the horiz. freq coil, which also doubles as the customer "Horiz. Hold" control) and C606. This capacitor is a mica cap, and tests fine in my old Heathkit capacitor tester (which can test for leakage at various voltages-- really a handy thing, by the way). I don't have very many replacement mica caps around, but it so happens that I actually had a new 330pF silver mica, so I swapped it in-- but that didn't help. I also tried tacking in a 270pF ceramic (one of the few other high-voltage caps I had in that general capacitance range but lower than 330pF) in place of the 330pF just as an experiment, and indeed it did help slightly, but not nearly enough to get it in range. I don't know the expected resistances or inductances for the horiz frequency coil, as they aren't listed in the RCA service manual I have, so I can't be absolutely sure there isn't something wrong with the coil. It seems like it's within reason, though. I measure 77 ohms between points H and K, and 55 ohms between points J and K. Anyone know the correct values for this coil? I don't have the SAMS folder for it, but it probably has those values listed.
Other things I tried: Swapping the 6CG7 tube had no discernable effect. R606 tested okay, and replacing it with R's of different values had no discernable effect either. C602, C603, R602, and R608 are all okay too.
Any thoughts? I suppose I could "force" it to work by either trying lower-capacitance replacements for C606, or by "padding out" the horiz. freq coil with another coil, but that seems a bit dodgy. Still, it's kinda annoying to be soooooo close to having a watchable picture, but being not *quite* there! :-!
On the other hand, I did stumble on the cause of my overly-green raster. At the back of the CTC-5 "Deluxe" chassis in the area where the chroma section lives, there's a riser board with a number of power resistors on it. Well, there was a cotton-covered connecting wire dressed in such a way that it was practically *wedged* between one of those power resistors and an adjacent tube. Seems that over time, this had scorched the wire, even severing the conductor-- it was so bad that the wire literally *crumbled* at that point when I touched it. Fixing the bad wire got me a much more 'color balanced' raster. BTW, attached is a recent screen image, which also
illustrates the horiz osc problem.
Thanks everyone!
|