ctc-5 hv problem
 

Set was totally recapped about 5 years ago by me and haven't had any big problems since then but today I turned it on and sound/tuning is ok but no picture, then 2 or 3 loud pops and I turned it off quickly. I tested all the tubes and look ok. Tried it again and popping did not reoccur but still no pic, I was still getting hv though (pulled the anode connection off the hv rectifier and getting sparking) Now I get zip hv and the hv rectifier doesn't even look like it's lighting up. Any suggestions on where to start? Guess I gotta pull the chassis, arghhhhh. I have to first try to see if can get the hv back before worrying about anything else, I might have screwed something else up while messing with testing the tubes to make it go away, or something croaked later like the flyback but it looks ok visually. Both fuses on top of chassis check ok. Oh well now I have a new project.
One more thing, while I still had some hv there I noticed the hv rectifier had little microscopic sparks visible at the bottom, I thought that was kinda strange. But when it originally acted up today I had a solid state replacement instead of a 3a3 in there anyway so that tube didn't cause the problem. The 3a3 I put in on the second turn-on was doing that sparkly thing (barely visible). thanks
Frenchy

Maybe you will be lucky and it is a corroded/broken terminal in the socket of that 3A3. I hope it is not the fly but if it is I hope you save the old one because I think if we can't find a replacement that maybe the old one could be chemically disassembled to reveal the wiring secrets and maybe we could rebuild the old with new wiring! I may try that if my CTC-15 ever goes out.

I will put the monster on the bench this week and recheck all the tube placements and wiring etc. and see if anything under-chassis looks like it was arcing or frying, and go from there. Darn it, this was the first time I've tried to power it up after it turned 50 years old, what a letdown.
Frenchy

Sorry to hear that you had that happen... It's happened to me more than once, and I know how it feels!

It sounds like an arc. If you didn't smell anything burnt, that is. First, check the HV fuse. I think in that set it's near the damper tube, but it's been a few years since I looked at a 5. An arc can also blast the rectifier, or possibly the shunt tube. Was the weather humid??? Those have a problem with the high voltage arcing through pin holes in the CRT shroud to the metal CRT mount hardware. Or, arcing in the cage. If the fuse is blown, replace it and turn out all the lights in the room. Watch carefully with full view, even have another person watching. Turn the set on, and try to see where/if it arcs. Pull the cap off the rectifier and see if the RF is there. If so, then suspect the rectifier or the 30 KV doorknob cap below the rectifier socket.

No promises, but that's where I'd start.

Charles

ok thanks I'll update when I have the chassis pulled out and can see if I can even get the HV to come back, arcing or not. It has been hot and somewhat humid here in So Calif lately but I've also had the A/C cranking like crazy for the last month too.
Frenchy

Hi frenchy, before putting this heavy beast on the bench:
can you check the hv d.c. current with a hv probe at the cathode of the 3A3? Does the anode of the shunt regulator is red glowing?
There are several reasons for arcing. One of the most fatal is a short in the insulation cone which is placed on the metal cone of the 21AXP22A.
Another reason might be a short in the focus regulation unit. If there is a short, the flyback won't work properly. Check the focus control inside for burnings.
Eckhard

Hi frenchy.
I would check the heater wire for the 3a3. It could be arcing to the hv cage.
The 5 is a monster chassis.
Good luck
ED

all the tubes check out on my heathkit tester and glow, except now the 3a3 doesn't seem to light anymore (I could see it lighting up good when the voltage came up to speed before), tried multiple 3a3s so the culprit doesn't seem to be the 3a3. I'm pretty sure I replaced the focus pot when I recapped it. I'm pulling the chassis since it is just too darn hard to see or reach anything on this set with it in the cabinet and I'm already getting myself into trouble doing that. thanks!
Frenchy

When I first got my CTC-5 it worked but when I tried it the next day, no picture. The story of how I got it back was long, as I created additional problems along the way. Anyhow, I THINK the initial problem was a short underneath the video board. I had missed it as it was under an IF shield. A terminal strip and attached cap had turned to crispy critters & apparently that killed the raster. At least I think that is what happened. The chances of that being the case here are pretty slim but I did want to relay the experience.

Frenchy
When you get the chassis out check the two black wires next to the red hi voltage wire. {see picture}. Of course this is just a guess on my part but I did have the same problem with the ctc 5 that is at my moms house. I took one out of a newer parts chassis and replaced it. Yes that fly looks like hell, I put pure silicone rubber on it. I clean the fly and then glob it on with my fingers, Nice and thick. It will keep the tire from moving when it gets warm and also helps cool it down a little. A working ugly fly is better than a dead one.

At the risk of sounding smug, why don't you use a voltmeter on it? There should also be a resistance chart available in the Sams, too. Do some good old detective work. Good luck.

Y'know, this is wild-Where else but on AK could you have a problem w/something as exotic as a 50-yr-old color TV, & get a dozen or so replies on how to fix it...from all over the world...Well, at least N. America & Germany...Astounding, simply astounding !!

I bet your rectifier socket is bad. I've replaced enough of them on RCA's over the years, including my own CTC-10C.

All of the theororists, guessers, second guessors. I would say you have a bad kine-o-derm. Amazing! I think somebody should do a little bookmaking on this one. I still say get a voltmeter and start checking it out!

I'll pull the chassis Monday, my girlfriends coming over this weekend, first things first : )

Yes, THE SET COMES FIRST!!!

Obviously, I have no life....... :tears:

A message to Frenchy about this weekend
 

Girlfriend's coming over, huh? :banana: :banana: :banana: :banana:

Hi: If you have an original RCA schematic (maybe on Sams, also) for the CTC-5's, look closely at the CRT drawing. You will see that the "shroud" is also the filter capacitor for the high voltage supply, with a coating (auqadag?) inside and outside of the plastic base material. Deterioration of the plastic, particularly in the area of the mounting hardware, no doubt might cause arcing. I have a 5-N on which I just finished chassis work. I will now be faced with the HV problem. I plan to de-mount all CRT hardware, remove the shroud, and inspect for pinholes, etc., and will have HV putty, and corona dope on hand. I will post any info that might help. What a mess!!
Kevin G.

I think this may have been my own fault, I think I was running it without the IV2 focus rectifier in the set, I had probably pulled it months ago testing out another set. Could this have damaged anything? Damn. The fuses on top are still ok, but the underchassis soldered-in 2 amp fuse was blown. Someone (the factory?) had put a piggyback fuse clip onto that fuse with a 3 amp slowblo in parallel so that circuit is still closed. Now I'm worrying this was put on by someone when it shouldn't have been. Anyway I pulled the chassis and retested all 5 tubes in the hv section and still zippo hv spark. I don't have any hv probes, only minimal testing equipment. If the IV2 was totally missing, what could that have fried, if anything? thanks

No. If this is the only fault, the set will operating again when you replace the 1V2.
But you reported some kind of arcing. This seems to be a more serious problem.

Eckhard

I did that with a 6bk4 once and that set put on a good light show and my ears were ringing the rest of the night. NOW I make sure I put the tube I am checking in the set I got the replacement from.
With the focus voltage missing and the set running for a period of time may have damaged the crt. I figured the damage starts when the guns are warmed up all the way. But I am not sure on that. Also the arc may have been inside the crt. Did you notice a blue glow from the neck of the crt?? The fuse sounds like someone put in a replacement. When they put in the 2 amp it more than likely opened a week later and then they put in the 3 amp slo blow.
Try this, See if you can get your hands on a high voltage probe. Put all the tubes back in and replace the fuse with the correct one. Disconnect the crt hv lead and socket.
Then check and see if you get hv. If you do, Then hook the crt back up and see if the hv goes down and look for arcing. If it does then you know it is the crt.
Please note that I am only guessing. I would need the set in front of me to know for sure what is going on. ALSO.. Please be careful with the hv, It is nasty stuff. I won't even get into the mistakes I have made with that.
ED

That's what I've done today, the chassis is pulled and I am still getting no HV at the 3a3 hv terminal (grounded screwdriver) with all the tubes now in it and tested. I did not notice any popping or blue glow on the crt but then I was only looking at the screen when it happened, and didn't see anything there. Didn't see it when I had the back pulled either, all 3 guns were lit normally. It was pretty loud so I assumed it was an external pop and didn't see anything on the screen whatsoever either. Perhaps testing the crt with my crt tester would be in order. But I still have no hv period so I kind of assume the chassis problem is all I have and did not involve the crt. Would good readings on the crt test pretty much rule out damage? I forgot I do have a HV probe in the closet so I will see if I can remember how to hook it up and maybe make some measurements on the chassis. I do get a teeny tiny spark when I physically touch the screwdriver to the terminal, so there is SOME voltage on the 3a3 terminal at least, not nothing. Flyback looks great and I can't see where anything 'popped' anywhere else. Frenchy

How was the weekend?? :banana: :banana: :banana: :banana: :banana: ??

:banana: :banana: :banana: :banana: :banana: :banana: : ) : ) : )

frenchy.
In a way that is good news. Remove the plate cap on the 6cb5 and see if you get a arc from the tube. Should be about a 1/4 inch long when it jumps to the screw driver. If you do, Put the cap back on the 6cb5 and Pull the cap on the 3a3 and see if you get a arc from the cap that comes out of the fly. That way you can figure the fly is working. Did you check the 6bk4 tube? It could be that is the problem. The caps or resistors in the hv regulator may be bad.
I am not sure what the crt tester would show if a crt is damaged by no focus voltage.
I would guess the crt went to air and the heaters would go out? That will give me something to do when I run into that again.
ED

I get no spark whatsoever on either the the 6cb5 or the 3a3 cap tests. I tested the 6bk4 and it's a new one I swapped in after the hv failure.

Really, No arc at the 6cb5. This is interesting. Check for the b+ at the fuse at both ends, M4 on my sams 3/4 amp It Should be around 380-390 volts. Also please check the horz tube plate cap. With it disconnected from the tube, Check and see if you get a voltage reading. If b+ is on the fuse and horz plate cap try replaceing the horz out and damper tubes. They may check ok on the tester but when in circuit and under load they don't work.
Also do you have a variac? And what is the ac line voltage you run the set at?

ED

Me again
I just caught my self and yes I am a dumb ass.
Please recheck the 6cb5 for an arc. The plate cap must be on the tube to see the arc. {See picture} You do get one with the cap off but it is vary small. This is a b-w set but it should do the same thing on your set.
It was the only set I could get my hands on asap.
ED

ok thanks will try these tests tonight.
Frenchy

Hi frenchy, read this thread
http://audiokarma.org/forums/showthread.php?t=30364
which is discussing similar problems. At first I would check whether the horizontal oscillator is working and whether there is a negative voltage at the grid of the horizontal output tube. What is the horizontal output current (measure at the cathode of the horizontal output tube or remove the horizontal fuse and measure the current across the fuse). Be sure that you are not in contact with the +b voltage.

Eckhard

Test results:
replaced 6cb5 and damper, still zero HV spark jump to ground
3/4 amp fuse - about 400v at both ends
3/10 amp fuse above it - barely reads any voltage, < 1v both ends (what's this one for? Probably shouldn't have just measured it without knowing what it was but did anyway, oh well)
6cb5 cap, connected - no spark whatsoever
6cb5 cap, disconnected - 165 v ??? Ed said this should be B+ too?
I am running at normal line voltage, 117 v maybe.

The 3/10 amp fuse is for the horz current so Don't worry about that yet. I dug out my 5 and did a double check on the 6cb5 cap voltage and I get 385vdc on that cap. Also my ac line is set to 114 ac so it would be lower than what you would get at 117vac. I think you found your problem. Just to make sure, Check pins 4-5 on the 6cb5 and make sure you have drive voltage. It should be around -30 vdc. Also check pin 7 on the 6cg7 {horz osc}. Should be around - 70vdc. Lets make sure the b+ is getting into the horz osc. Now please go to the yoke plug and see what you get on pins 7 and 3 and Make sure the yoke is connected. The voltage should be at b+ or a bit lower.
Ed

frenchy.
Here is a picture of the yoke plug. As you can see there is a jumper.
This jumper is a interlock so the horz will not turn on with the yoke disconnected. It could damage the set if it was turned on with the yoke disconnected and there was no interlock.
ED

ok I will check this stuff tonight. Well, tommorrow night, girlfriend is coming over tonight (yes again : )
-- What is the overall effect of testing with the yoke disconnected as far as me getting normal voltages in the hv section, spark etc.?
--At first glance what does it sound like the culprit might be with that low voltage at the HO cap? (I hope it's not that I'm just a dummy and all I had to do was plug the 1V2 back in while I still had the chassis in the set and the yoke still connected.)
--Do I have to do all the measurements with the yoke connected or not? Right now I'm testing it on a bench away from the cabinet, I didn't know there was an interlock in the yoke plug. I saw a 'HV interlock' on the schematics but I coulodn't see one obvious on the chassis so thought maybe there wasn't really one there.)
Thanks! I told my girlfriend I might know 10,000 times more about fixing tvs than HER, but you guys here know 10,000 times more than ME! : )

frenchy.
You do need the yoke connected to get normal voltages. I think that may be why you have low voltage on the horz tube cap that goes to the flyback. Also I think most tube color sets have that type of system. In a way it does cut off the hv so it could be the hv interlock, But it may be the line cord you are looking at. Also I may be useing the wrong word. {interlock} Throw in the 1v2, put it in the cabinet and see what happens.
I would try and lower the ac line voltage, Just in case the arcing is still a problem.
That would be great if it was just the 1v2.
Good luck and have a great evening.
ED

ok I will lug it back into my bedroom and plug it all back in and try it, I've guess I've fixed black and white sets before and was used to expecting good HV to be at the anode wire even with the chassis out. The interlock for HV on the schems was either on the cap wire for either of the two big HV tubes (6cb5 or 6bk4, don't remember offhand) but I never saw that in the chassis itself. Crossing my fingers, thanks
Frenchy

Thanks everybody for helping me with my ignorance on some basics, set is working fine again after fully hooking it up to the pic tube and popping the 1V2 back in there. It was a combination of dumbly not putting the 1v2 back in the set months ago to begin with + not noticing the 1v2 was absent while debugging the installed chassis since that tube is buried way down in the cage + the popping spooking me into thinking it was something like a bad flyback and not a missing tube + not knowing about the interlock design of the yoke plug. I just have to put the HV cage back in now. Whew!
Frenchy

Frenchy
Glad to hear that. Can you post a picture of your set. I bet it is a cool looking set and has a nice picture.
ED

Here she be, this is an old pic from couple of years ago but it looks the same now. This thing is really a survivor, there is a crescent-shaped cracked indentation around the channel changer where you can tell somebody tipped the thing over once and it slammed onto the floor on it's side once but it refuses to die! Even the survivor VP-1000 laser disk player on top of it has since croaked.

Two good weekends in a row!
:banana: :banana: :banana: :banana: :banana: :banana: