CTC-4 Director 21

[SwizzyMan]

Sounds like too risky of an operation. Let's just get it going first i guess.

[SwizzyMan]

I replaced a shorted 12BH7 (R-Y G-Y Demod) and a shorted 6AG7 (Demod driver) tube hoping I would see at the least a bit of improvement. Well there was none whatsoever, if anything the picture quality has gotten worse by just sitting for a mere month. I still have no red which pisses me off since I really thought the shorted R-Y demodulator tube might have given me a hint of red when replaced. At one point I had red. Once I did a recap, I lost it which doesnt make any sense to me. Also I still need to figure out what all the interference associated with the color being present in the picture is all about. While I had the chassis on the bench testing voltages and checking wave forms, a resistor started smoking. It was a 10K 2watt resistor feeding a 285v supply off of the demodulator coil, its value has now risen out of tolerance so I will replace it regardless. Not sure if this may be an issue with the total absence of red. There is also a thick line on the side of the crt when the set it on, doesnt look like a drive line to me. Ive got my work cut out for me and I still have a lot to learn about these sets even though Ive restored two other roundies. Anyone here have any ideas on where i would even begin to look?

[DaveWM]

if it had red at some point before doing a recap, then you should check your work.

also, checking pin voltages is 1st (think you did this early on and there were issues with voltages at CRT pins)

if the Purity is way out, then getting good red will be an issue as well.

How does the CRT check for emissions and cut off?

[old_coot88]

It looks like the 3.58 oscillator isn't running.

[DaveWM]

good point about the osc, I am used to seeing the rainbows in the pic, but that is when its not synced up, could be not running at all. Get the scope and see if you can get a wave form from the color osc.

[Hagstar]

Rattle in a crystal sure is a bad sign. These are easily obtainable (eBay etc.) but beware most are for transistorized TVs, a larger earlier one is what you want. Usually these are in the HC33 size case.

[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.

[andy]

///

[jr_tech]

I think that this handy tip should have been made a sticky:

http://www.videokarma.org/showthread...hlight=degauss

jt

[Electronic M]

Originally Posted by jr_tech

I think that this handy tip should have been made a sticky:

http://www.videokarma.org/showthread...hlight=degauss

jt

I've made it into one.

[dieseljeep]

Originally Posted by Electronic M

I've made it into one.

I picked up a Radio Shack bulk tape eraser, that works great! It's a black plastic unit, that looks like a travel iron. It's a real powerful item, that can be used to demagnitize, just about any kind of magnetic media. It also works well as a deguasser, even though, I still have the first RCA DG coil, I bought over 50 years ago.

[kvflyer]

I too use a Radio Shack bulk eraser. It is very powerful and does the job.