CTC-4 Director 21

[SwizzyMan]

It actually turns out the smoking resistor is a 5k 10w coming off the color take off coil and feeding another 285v supply. I dont see any brown spots where burning has occurred on the resistor itself and I know a 10 watt dissipates a lot of heat. So it may just be dust on top of it burning off. But i recall never seeing any smoke until now coming from it. I checked tubes associated with it and none were shorted. I noticed that the resistor has a connection to G1 of the AGC amp tube. I had been adjusting the AGC in hope it may have given me a better picture, not sure if its set too high, but I dont think adjusting the AGC would cause this.

[Electronic M]

Originally Posted by SwizzyMan

It actually turns out the smoking resistor is a 5k 10w coming off the color take off coil and feeding another 285v supply. I dont see any brown spots where burning has occurred on the resistor itself and I know a 10 watt dissipates a lot of heat. So it may just be dust on top of it burning off. But i recall never seeing any smoke until now coming from it. I checked tubes associated with it and none were shorted. I noticed that the resistor has a connection to G1 of the AGC amp tube. I had been adjusting the AGC in hope it may have given me a better picture, not sure if its set too high, but I dont think adjusting the AGC would cause this.

That resistor is a red flag odds are there is a short or a mis-biased tube drawing too much current through it. Do voltage checks in the area around that resistor and on any tubes it feeds.

[SwizzyMan]

It has to be an improperly biased tube causing the resistor to overheat. I checked almost everything downstream of it and found no shorted components. Will check voltages later.

[SwizzyMan]

Was going to check voltages so I reconnected both resistors. After pulling the noise inverter 6u8 since it was connected to the resistor (thinking this may be the mis-biased tube.) to check for smoke, I got none. I put it back in the socket and still no smoke. The 5k resistor is no longer smoking and burning up. It is still warm to the touch but not burning hot. I now need to replace the 3.58 crystal. Phil Nelson was kind enough to donate a crystal to the cause so Im waiting on that getting here.

[DaveWM]

shorted tubes can smoke resistors, and shorts can be intermittent.

[Hagstar]

I wasted a lot of time on my CTC-4 thinking Hickok tested meant something. Indeed failure to work as a chroma amp or intermittent shorts weren't always detected. Tubes are cheap enough, and those 6U8s and AZs are considered expendable under such heavy use. I just order NOS (usually Sylvania or GE) for all critical tubes for any color set so old and keep the old ones for emergency/if they work spares.

[SwizzyMan]

I'll look around for any shorted wires, but my next order of business is to figure out how to get rid of the interference when the chroma signal comes in. It makes the picture unwatchable. I also have a bit of artifacts on the black and white signal now. I may just shotgun replace all resistors on the video board for good measure, but the chroma signal interference might be a different story.