HV Arc on CTC-5

[TVBeeGee]

Any advice on high voltage arcs on a CTC-5? I have not yet measured the HV on my "new" CTC-5, but it has arced once and we assumed this was due to a combination of dirt and humidity. (The chassis has been recapped some time ago by a different owner.) In addition to a thorough cleaning of the chassis and especially the HV cage, would it also be a good idea to remove and clean the area between the CRT and its plastic insulator, or is this area normally sealed enough to prevent dirt and moisture from getting in? I do not plan to power the set again until I have protected the HV from arcing. After the arc occurred, we still had horizontal sweep and high voltage, but vertical deflection was missing. I don't know if the missing vertical sweep was related to the arc. Could be a different problem, even a bad tube socket. The set was working fine before this attempt to power it, which caused the arc during warm up. The set had been sitting in a garage for some time before this attempt to power up.

[Electronic M]

If you don't know where the arc is fixing it can be extremely difficult. Sometimes it is worth while to get it to repeat to find it.

Cleaning the dust inside the HV cage is a good start, but don't go crazy on the flyback...if you break a lead off the fly it can be game over for the set.

The front of the shroud tends to stay fairly clean inside, but the area near the yoke can get fairly grimey...if it's arcing in the shroud the yoke end is where I would first look.

The 21AXP is designed t run at 25KV and the weak HV system of a CTC5 is having a really good day if it can deliver 20 with the pull down regulator unplugged....The HV cannot not shoot up to 100KV and saw the neck off the CRT like a Zenith CCII with bad safety caps so the CRT shouldn't be harmed. Flybacks can also take around 10 seconds of arcing (especially when cool) and be okay.

[damen]

If there was no vertical deflection after the arc I would check around the vertical output transformer and vertical centering control. These parts can also make a loud "snap" when they fail.

[Yamamaya42]

Originally Posted by Electronic M

If you don't know where the arc is fixing it can be extremely difficult. Sometimes it is worth while to get it to repeat to find it.

Cleaning the dust inside the HV cage is a good start, but don't go crazy on the flyback...if you break a lead off the fly it can be game over for the set.

The front of the shroud tends to stay fairly clean inside, but the area near the yoke can get fairly grimey...if it's arcing in the shroud the yoke end is where I would first look.

The 21AXP is designed t run at 25KV and the weak HV system of a CTC5 is having a really good day if it can deliver 20 with the pull down regulator unplugged....The HV cannot not shoot up to 100KV and saw the neck off the CRT like a Zenith CCII with bad safety caps so the CRT shouldn't be harmed. Flybacks can also take around 10 seconds of arcing (especially when cool) and be okay.

"saw the neck off the CRT"?
That's an exaggeration, I assume? can't really happen... right?
Although, it does remind me of a failure I had in a BarcoData (crt) projector long ago, it had been working fine for months, clear and bright, and suddenly went dark with a loud popping sound , (hv arcing) when I took it apart, I found the HV pcb had failed , common problem on these, but not only that, a tiny crack had been blown in the blue crt, right where the inside dag ended, allowing the hv from the inside to jump to the yoke.
I could not believe what I saw, how THE HELL did that crack get there? It could not have been there before, cause it would have caused vacuum loss.
Did the hv blow through the glass? Perhaps it did...

[Electronic M]

Originally Posted by Yamamaya42

"saw the neck off the CRT"?
That's an exaggeration, I assume? can't really happen... right?
Although, it does remind me of a failure I had in a BarcoData (crt) projector long ago, it had been working fine for months, clear and bright, and suddenly went dark with a loud popping sound , (hv arcing) when I took it apart, I found the HV pcb had failed , common problem on these, but not only that, a tiny crack had been blown in the blue crt, right where the inside dag ended, allowing the hv from the inside to jump to the yoke.
I could not believe what I saw, how THE HELL did that crack get there? It could not have been there before, cause it would have caused vacuum loss.
Did the hv blow through the glass? Perhaps it did...

I have not experienced it personally, but there are several accounts here of fist gen solid state Zenith color sets (CCII flatchassis) having the HV climb so high (due to safety cap failure) and the HV arcing through the bell glass to the yoke....the arcing would heat the glass, the glass would crack and the neck and yoke would drop onto the chassis....It did have to be ran in that state for a while so this story is usually told by TV repairmen about customer sets since most VKers are smart enough to turn the set off when it makes bad noises. I've heard this story repeated enough that I don't doubt it's veracity. I also had the safety caps fail on one of those sets and for the 3 seconds it took me to yank the cord I saw a rather spectacular light show.

[old_tv_nut]

Originally Posted by damen

If there was no vertical deflection after the arc I would check around the vertical output transformer and vertical centering control. These parts can also make a loud "snap" when they fail.

Ditto -- are you sure there was a high voltage arc and not something else? Instant death of the vertical due to a high voltage arc is much more likely in a transistor set than in a tube set.

[JohnCT]

Originally Posted by Electronic M

I have not experienced it personally, but there are several accounts here of fist gen solid state Zenith color sets (CCII flatchassis) having the HV climb so high (due to safety cap failure) and the HV arcing through the bell glass to the yoke....the arcing would heat the glass, the glass would crack and the neck and yoke would drop onto the chassis....It did have to be ran in that state for a while so this story is usually told by TV repairmen about customer sets since most VKers are smart enough to turn the set off when it makes bad noises. I've heard this story repeated enough that I don't doubt it's veracity. I also had the safety caps fail on one of those sets and for the 3 seconds it took me to yank the cord I saw a rather spectacular light show.

Saw a few of those. American Radionics made the safety cap that wasn't very good about safety.

When a section of the cap would open, the HV in the Zenith SS vertical chassis would supposedly hit 70K or more. It would immediately arc from the neck through the glass and into the vertical winding of the yoke. There would be a puncture in the neck under the yoke. Sometimes, the neck would break completely.

Zenith covered the repair even out of warranty, which was a new tube, a new yoke, the vertical output module, horizontal output, and a new safety cap made by Sprague IIRC (it looked like an oversized Orange Drop.

John

[old_coot88]

Originally Posted by Electronic M

I have not experienced it personally, but there are several accounts here of fist gen solid state Zenith color sets (CCII flatchassis) having the HV climb so high (due to safety cap failure) and the HV arcing through the bell glass to the yoke....the arcing would heat the glass, the glass would crack and the neck and yoke would drop onto the chassis....

I can vouch for it. Neck severed right where it joins the bell with a perfectly clean cut.

[TVBeeGee]

Damen, this was a pretty loud bang instead of a loud snap. It was more like a gun firing, so I do hope it was "just" an arc. (We also didn't smell anything, if that provides any more info.) I guess we'll see when I start to get into the troubleshooting, but it will be at least a few weeks before that happens. My wife and I are in the middle of a household move currently, with all the associated chaos that goes with that.

What am I facing if the loss of vertical deflection does turn out to be a bad VOT or vertical centering control? Are replacements still available as old stock or used, or must I track down another set that still has a good one? Can these parts be rewound/rebuilt?

To everyone:
THANKS for your input! You might enjoy a little story about my own experience with a Zenith CCII. My father had one. One day, he phoned me to say that the set was making a loud bang when turned on. I warned him not to run it like that and I would come over a take a look at it. I found the high voltage arcing at the CRT anode cap. So, I discharged it, cleaned it up and put some corona treatment around the area. Powered it up again and found that it still arced not only there but also several other places!

I checked everything in the horizontal and high voltage areas, figuring that something had died causing a regulation problem, but everything seemed to be in order. I finally bought a new flyback. Yep, that was the culprit. It apparently had some shorted turns on the primary side that were resulting in the "Nikola Tesla Experience" at the output side. Fortunately, the CRT wasn't whacked in the process...and neither was I.

That set ran for decades after that with no problems at all. It was still working great when my father finally moved it to the curb after buying his first HDTV. Electronic_M on here writes that Zenith quality stays in even after the name falls off. It's true!

[Electronic M]

If it was a loud bang then a lytic or paper probably let go. HV is usually a squealing, hissing series of snaps.

[TVBeeGee]

Thanks, Electronic_M. This CTC-5 Deluxe was SUPPOSED to have had a full recap. I have observed numerous orange drops, so it would appear that the paper caps have been replaced. Don't yet know about the electrolytics.