Philco Predicta Holiday Set Flyback Arcing

[rca21d645]

After working on several of my other older television sets, and successfully repairing each one, I figured that now I would be ready to attempt repairing a Philco Predicta Holiday set of mine. I've got it very close to working, but I noticed that as soon as the screen lit up the flyback started arcing. I immediately unplugged the set as this happened to keep it from potentially damaging the flyback further. I figured this must mean that the flyback needs to be coated in something like corona dope or silicone to fix this. Just to make sure that it was the flyback that was the issue, I took a second Predicta flyback that I had from a much less cosmetically nice Holiday set that I had been using for parts to fix this much nicer looking Predicta. This flyback also arced just like the previous one. With this in mind I wasn't sure if I somehow ended up with two bad flybacks, or if something else in the set could be causing it to arc. I know for certain the flyback itself is arcing and not another component because I could see the bolts of electricity coming directly off of the flyback itself. I'm leaning towards the idea that both flybacks happen to need recoating but any other suggestions of what the issue may be would be appreciated. I have already replaced the multisection resistor, the fuseistor, all the paper and electrolytic capacitors, and most of the resistors, and have made sure all the tubes in the set are good and working.

[Kevin Kuehn]

I'm no Predicta expert, but exactly what part of the flyback is arcing to what else(assuming to the chassis?) Maybe a picture could help.

[rca21d645]

Originally Posted by Kevin Kuehn

I'm no Predicta expert, but exactly what part of the flyback is arcing to what else(assuming to the chassis?) Maybe a picture could help.

I didn't think to take a photo at the time but it was arcing from one wire on the flyback to another. I circled the part on this picture where it appeared to be arcing.

[Yamamaya42]

Originally Posted by rca21d645

I didn't think to take a photo at the time but it was arcing from one wire on the flyback to another. I circled the part on this picture where it appeared to be arcing.

sounds like you have the same problem that Zenith had.

https://www.youtube.com/watch?v=KPyn6cmSQhQ
pay close attention about 5 min in, this may be the problem

[rca21d645]

Alright, I guess I'll see if removing some of the red board fixes it, but first I think I'll try sealing it with corona dope.

[Yamamaya42]

Originally Posted by rca21d645

Alright, I guess I'll see if removing some of the red board fixes it, but first I think I'll try sealing it with corona dope.

If it's carbonized you have to remove it first, no way around that.

[Electronic M]

Have you measured and compared your HV to spec? If something is wrong and HV is significantly higher than normal that could cause insulation breakdown...

And yes remove any carbon tracks along the path of arcing. Once an insulator carbonizes it essentially becomes a resistor and will continue to function as an arc path no matter how much silicone or corona dope you cover it with.

[rca21d645]

Alright, I got the arcing on video this time and it appears that my memory of where it arced was wrong. It seems to be arcing near the core of the flyback, nowhere near the red board. I also forgot to add that upon installing the fuse with a 5.6 ohm resistor, the fuse blew when powering it up. Video here: https://drive.google.com/file/d/1yjr...ew?usp=sharing

[Yamamaya42]

I am no expert on this, but that looks like a classic example of the outer “doughnut” becoming conductive due to inner carbon tracking, the only fix is to remove it all very carefully and inspect everything for any carbon burns and remove it, and then cover it with dope, sometimes you even have take the whole thing apart, ( ref Shango's videos ) down to the ferrite core to look for carbon tracks, cause sometimes it can burn a arc to the screw rod, but it does not happen very often.

[Electronic M]

Did you look at the arcing from the side of the flyback it is happening on? The camera angle makes the arcing look like it's on the far side of the fly from the camera or in the HV rectifier base behind the fly.

It's a good idea to check HV level before doing anything drastic. The Width pots in predictas have a significant effect on HV as does the load of the CRT. If the width is cranked and the HV rect isn't conducting and thus not loading down the HV, then you could be 6KV above spec and the voltage could be higher than the insulation was designed for thus causing arcing. They often didn't design much head room into flyback insulation so %15 over spec can be pushing the limits of the part.

[rca21d645]

Just an update, I gave up on the one flyback as when I discovered carbon tracking was on its red board, the whole board kinda split apart as I tried to remove it. I discovered that the second flyback had been arcing because the high voltage wire that loops around it had a part where the wire was exposed, causing it to arc to the chassis. After replacing this wire with one of the same size and rating, the television powered up with no arcing whatsoever. The picture is pretty blurry, but the tube can still get fairly bright so I think it may just need to have the focus adjusted, or it may be clearer once I finish replacing the resistors. I didn't mess with any of the couplates yet as I figured if it worked with them then there's no reason to mess with them and there was evidence that they may have been replaced previously. Apart from the vertical being a little touchy I don't think any of the couplates would affect the focus. Edit: Those spots on the screen are on the screen cover, I've been using the cabinet and tube of my parts set as I didn't want to risk potentially damaging the better set while working on the chassis. The tube is the original 21EAP4, as is the one in the good cabinet, but both tested good on my tube tester so maybe it just needs some time to wake up as well.

[rca21d645]

SO I tried moving the focus jumper around I think I got the picture to look a bit better, I also noticed as I left it on for a while the picture would clear up some more, but it still looks almost smeared, and most text is difficult to read. I'm assuming this is just because it still has the old 21EAP4 tube in it as I don't really see anything else that would be causing it that hasn't been replaced. I attached some photos for reference, with my RCA console to show the drastic difference in picture clarity, as both are also 21 inch sets.

[Electronic M]

The smearing looks to be horizontal only which would point to IF (alignment) or video stage issues rather than CRT. If on a blank raster the scanlines are reasonably defined then it's likely IF....you can verify by connecting the video from a DVD player or test pattern generator displaying a multi-burst frequency response test pattern to a scope then comparing the video waveform at the CRT. The ringing and smearing should be noticable on the scope in in the TVs video.

[Yamamaya42]

you have most likely seen this already, but in case not, http://www.earlytelevision.org/pdf/p...pair_final.pdf

[rca21d645]

I did some tweaking to the IF and I was able to get the picture to look a lot better with much clearer text, but after putting the chassis back in the set and closing it all back up, I plugged it in and C1 exploded, causing a ton of smoke to pour out of the set. I don't know what I could've done between working on the IF and putting the chassis back in, but I'm guessing that either the capacitor was already weakened from the times I plugged it in to test the fuseistor a month ago and it just gave up the ghost, or I may have somehow shorted it. Either way I'm going to have to wait for the replacement capacitor to arrive before I can continue working on it.