CTC-7 no high voltage

[SwizzyMan]

Hello all!,

Not sure if I am posting in the correct thread... So today I tried to run my CTC-7 with the chassis outside the cabinet. All tubes glow and crt filament lights up but I have no high voltage... I made sure all the cables were plugged in except for the audio which I don't think matters for the set to run. I smell a slight burning smell but no smoke in the high voltage section. I have not done anything to the chassis yet but it was sitting in 85 degree weather (not direct sunlight) for about 2 days. I had a raster and high voltage before I took the chassis out. Could some caps have gone off value while it was sitting? what is the problem here?

[ohohyodafarted]

If the horizontal oscillator is operating you should be able to draw an arc off the cap of the horizontal output tube. Take a long flat bladed screwdriver, and attach a ground wire to the shaft of the screwdriver. Elevate the cap on the horizontal output tube and carefully move the blade of the screwdriver under the cap to come into contact with the metal cap on the tube. You should be able to withdraw the tip of the screwdriver slowly and draw an arc off the metal cap on the tube. The insulated plastic plate cap must be connected to the metal cap on the tube. If the plate wire is disconnected from the metal cap on the tube you will not get an arc.

Assuming you do get an arc from the metal cap on the horizontal output tube, to the grounded tip of the screwdriver blade, then you can assume the horizontal oscillator is functioning. So if you get an arc to the screwdriver and no high voltage from the flyback, then you can suspect that the flyback may be defective, or you may have something else wrong in the HV cage.

Also, take the cap off the shunt regulator (usually a 6bk4) just in case your shunt regulator is dragging down the HV.

If you fail to get an arc off the horizontal output tube plate cap, then your horizontal oscillator might not be operating. IF this is the case, you will often see the plates of the horizontal output tube glow red hot. If the plates glow red hot, then disconnect the plate cap on the horizontal output tube so you don't risk damaging the flyback during further testing. Failure of the horizontal oscillator circuit, will prevent you from getting HV. That could be as simple as a defective Hor Osc tube or any of a bunch of other causes. Some sets were equipped with a fuse in the HV section that will blow if the Hor Oscilator stops running.

WRT the burning smell... look for a burnt resistor.

In any event you are going to need a schematic and some basic tools such as a volt meter to check voltages. I would start with the power supply. If it has the original power supply filter cans, feel them to see if any of them are getting warm. A warm filter can is a sure sign it is leaking or shorted.

Are you using extension cables to run the chassis outside the cabinet? If so did you make them and are you sure they are made and/or working correctly.

Good Luck, You are about to learn the basics of trouble shooting.

[old_coot88]

Take a long flat bladed screwdriver, and attach a ground wire to the shaft of the screwdriver. Elevate the cap on the horizontal output tube and carefully move the blade of the screwdriver under the cap to come into contact with the metal cap on the tube. You should be able to withdraw the tip of the screwdriver slowly and draw an arc off the metal cap on the tube.

Holy effin' (*bleep*)!! I had to read the above twice to be sure what it was sayin'. And you're telling a newbie to do this?? Got any idea how much current an arc direct-to-ground is is gonna draw thru the flyback primary and damper?
If you want to pull an arc off the H.output tube's plate, it's not necessary to ground the screwdriver at all (just be sure the handle is well insulated). You'll get an adequate 'air arc' since there's about 6KV of spike at the plate.

[Username1]

well, if you wanna see an arc, just turn it on with the plate cap off, but sitting
on the top of the cap, and slowly lift it and let it arc from the tube cap to
the wire.... Just lift the wire with something insulated.....

But a better way to to just wave a neon bulb around the area..... The electromagnetic
field will make the gas glow at above 50v.... Don't touch the wires from the bulb to
anything, and don't touch them, you'll get a shock.....

Be sure the horizontal output tube does not overheat. If the horiz. osc. is not
running the horiz output tube will overheat and the plate will begin to glow red hot...
You don't want that..... If it's not getting hot, then you may have lost one of the b+
supplies, or a bad fuse in the flyback if this set has one.....

You should hook up a speaker and see if you get sound, that may tell you if you get
some of the lower b+ supplies....

Look to power supplies first, also look to be sure you didn't pull off a wire or something
when you took the chassis out.... Good luck...

.

[Eric H]

Leave off the ground! It will arc to the blade without it. You do not want to ground those connections to the chassis!

Before you do anything though I would check to see that the horizontal Oscillator tube is lit and making good contact.

The solder joints on the tube sockets can get flakey with age and get intermittent with age.

[Kamakiri]

I never had the "stones" to play that arc-to-screwdriver game.

I have a neon bulb attached taped to the end of an empty Bic pen body. I hold it close to key components. If the bulb lights, there's HV.

Much safer IMO.

[miniman82]

Are you sure you plugged the yoke in? There's a jumper that kills HV if the yoke is unplugged. Also the vertical section will continue to run with the yoke disconnected, which makes it very hot with no load. You should pull the vertical output tube if running sans yoke. Have you recapped the horizontal board yet? If not, you probably lost H-drive and the h-out tube is probably overheating. Look for the plate of the H-out tube to glow red in a low light situation, that will be a dead giveaway that you lost your horizontal wave form.

[SwizzyMan]

Originally Posted by Username1

well, if you wanna see an arc, just turn it on with the plate cap off, but sitting
on the top of the cap, and slowly lift it and let it arc from the tube cap to
the wire.... Just lift the wire with something insulated.....

But a better way to to just wave a neon bulb around the area..... The electromagnetic
field will make the gas glow at above 50v.... Don't touch the wires from the bulb to
anything, and don't touch them, you'll get a shock.....

Be sure the horizontal output tube does not overheat. If the horiz. osc. is not
running the horiz output tube will overheat and the plate will begin to glow red hot...
You don't want that..... If it's not getting hot, then you may have lost one of the b+
supplies, or a bad fuse in the flyback if this set has one.....

You should hook up a speaker and see if you get sound, that may tell you if you get
some of the lower b+ supplies....

Look to power supplies first, also look to be sure you didn't pull off a wire or something
when you took the chassis out.... Good luck...

.

There is a set of two fuses one looks blown but they are near what I think is the agc board and not near the flyback but that may be a problem.

[SwizzyMan]

Originally Posted by miniman82

Are you sure you plugged the yoke in? There's a jumper that kills HV if the yoke is unplugged. Also the vertical section will continue to run with the yoke disconnected, which makes it very hot with no load. You should pull the vertical output tube if running sans yoke. Have you recapped the horizontal board yet? If not, you probably lost H-drive and the h-out tube is probably overheating. Look for the plate of the H-out tube to glow red in a low light situation, that will be a dead giveaway that you lost your horizontal wave form.

From what I think I am seeing I don't think the Horiz output tube is even glowing.

[SwizzyMan]

Turns out the Horiz output tube had to just be wiggled around in its socket a bit so it made connection... Duh I feel kind of dumb

[Phil Nelson]

To avoid these little episodes, I begin every restoration by thoroughly cleaning all tube pins as well as the sockets. It's much less time consuming than trying to diagnose mysterious problems that are simply due to a little dirt or corrosion.

Phil Nelson

[old_coot88]

And don't forget to squirt the service switch (if any).

[rca2000]

Originally Posted by SwizzyMan

Turns out the Horiz output tube had to just be wiggled around in its socket a bit so it made connection... Duh I feel kind of dumb

You must remember the HO tube filament is HEAVY...I think 2.5 amps or so. and only 6.3 volts. SO...just like in old car 6V electrical systems... or a microwave oven magneteon filament...ANY corrosion or loose connections...WILL result in no fliamant or a filament too weak to work !!

[holmesuser01]

My CTC-7 had bad ground stakes on the horizontal oscillator board that caused the previous owner to throw it out. Fixed the stakes, and the set runs. Has all OEM tubes, except the video output, and the vertical output... both have 1971-72 date codes on them.

Glad you got it going again... for now.