Zenith 19L25 Chassis Restoration - Advice?

[newhallone]

I bought sensor safe rtv at the auto parts store. Worked great for my Zenith. Sensor safe is acid free.

[jr_tech]

Exactly! the stuff that smells like vinegar can eat copper wire/ circuit board runs.

http://newsgroups.derkeiler.com/Arch.../msg01830.html

jr

[RitchieMars]

Sensor safe RTV... sounds like a good idea. I don't think I need anything "eatting" my flyback. I was just at AutoZone awhile back with my dad. Maybe I'll check there and Advance and see what they have.

[RitchieMars]

I was just thinking back on something that I thought I'd throw out there. It seems like when I installed my 4uF capacitor which filters the 12BY7 video amp, I seem to recall that I got the capacitor awfully hot. Seems like I had some trouble positioning it or something and the 100uF that filters the sound take-off coil is right next to that and shares a ground terminal. These capacitors were awfully little compared to many I put in. I wonder if I just got them too hot and damaged them.

[RitchieMars]

I went out today and got some sensor safe blue RTV to coat my flyback. I coated the bottom half of my flyback where the wax came off, which effectively covered it a blue "icing."



After powering up the set and monitoring it, I've noticed now that that the "hiss" is gone, along with that troublesome blue arch. Still another trouble remains...



I kept hearing a little "tic.. tic, tic..." coming from somewhere down here, and this time it doesn't seem to be arching from the flyback itself. I turned out the lights and could make out a faint little arch jumping from somewhere on this copper-colored thing to the cadmium-plating support bracket below it. I didn't hook up an input, but noticed that I couldn't seem to get any horizontal sync. I'm inclined to think that there's a bare spot in one of these wires going to or from the 1B3 that's leaking somewhere.

[wa2ise]

I see a fair amount of dust and such on that tan colored piece of plastic. That dust and dirt can create leakage paths for very high voltage. Cleaning it may get rid of that tic-tic-tic.

[Phil Nelson]

Isopropyl alcohol usually cleans up that soft soot pretty well. I'd clean everything you can reach. A soft artist brush is good for getting into tight spaces.

Phil

[RitchieMars]

I took some time to clean up around this area with isopropyl alcohol, a small brush, and some cloth and I think I got rid of a ton of dust and black smut. I checked the wires, made sure they looked reasonably clean and cleaned up that plastic bracket and the area around the 1B3 tube.

Trouble came after I powered it up again. After about 10 seconds, I got some vicious arching from what looked like the bottom of the 1B3 tube socket. I didn't have to turn out the lights... it was just a sudden, wicked scorch of blue and orange. I didn't sit around and watch the show, obviously.

I took a close look at it and could only figure that maybe some of the alcohol got in there and didn't dry completely? I powered it up again, and saw no lights but heard a sizzle so I shut it off again and tried to blow it out. After the third time, the sizzle faded to barely nothing, but I can still hear a little hiss or two here and there from the bottom of the tube socket.

Gosh, if it's arching inside the bottom of that enclosed tube socket... I don't see any way in the world of getting to it.

[Phil Nelson]

Remove the tube and let it dry overnight.

[RitchieMars]

UPDATE: Oookay, apparently she's fine now...? I went back in there to poke around after I posted this and the set powered up without any problems. I hear no hiss from the flyback, no sizzle from the 1B3. Just the nice soft hum of the transformer and a purring raster. Maybe I really was just a little too heavy-handed with the alcohol, after all.

Point taken, though. I'll make sure it has plenty of time to dry overnight and I guess I'll plug up my inputs tomorrow and see what kind of picture I'm getting. Sitting as it is, the horizontal won't hold steady no matter what I do. I hope it's just the lack of signal.

[leadlike]

It's possible the leaking of the flyback threw off your horizontal frequency. Probably adjusting the H-lock coarse coil will throw you back into range.

[kvflyer]

Originally Posted by wa2ise

I see a fair amount of dust and such on that tan colored piece of plastic. That dust and dirt can create leakage paths for very high voltage. Cleaning it may get rid of that tic-tic-tic.

Yes, I would certainly agree. I have an air compressor. But find that even though they cost too much, those cans of compressed air for computers and keyboards are excellent for a delicate job like this. And, careful application of liquid cleaners with Q-Tips gets the job done. Sounds like it takes forever but sooner than later, you sit back and it is done and nothing is ruined.

[RitchieMars]

Without a doubt, that wasn't the easiest spot to clean up. I managed to get most of the dust and black smut out of there, though.



I went ahead and coated a little more of the flyback up along the backside and towards the top of it. This flyback must have sat under layers of dust for years before I bought this set, and even though I had done a "cleaning" in that area before, I was very gentle about it. It didn't help any that this was all right in the path of the falling chunks of plastic from the yoke cover. Someone had suggested that I coat the flyback with something before, but I was caught up in chase of hunting down all the other problems that I never got around to it until now. I'm glad I did. Cleaning this up and coating the flyback seems to have really helped, and I'm not hearing or seeing any signs of a leak anywhere now.

After hooking up my coaxial cable, I was able to see that my horizontal was way off but after running the set for a few minutes and adjusting a few things, I got it to hold on most of the channels although it's back to losing sync when I change channels. It would stay that way for awhile at first, but now it's more of a 2 or 3 second delay.

I can't say that my contrast has improved, so I'm thinking I should try substituting that 4uF capacitor with another with the possibility that it may be leaking. As I said before, I think I might have gotten it too hot when I installed it.

[RitchieMars]

Alright, now that my high voltage leak is patched up, I feel considerably better about taking live voltage readings on this set. I took a few earlier, but I noticed that the readings change noticeably depending on what channel the tv is set to, etc, so I looked in my schematics and it say's to take DC readings with no signal present, set to channel 2, and "normal" setting of controls. The last part of that I have a question about...

What would be considered "normal?" As in, should I set the brightness, contrast, AGC delay, etc, to their middle positions? Looking back at the schematics I posted before...



I'm wanting to check out this area and see what's going on with my contrast control. Maybe I'll have to take some measurements and adjust some of the controls and take note of what changes? I guess I just don't want to waste time giving you guys voltage readings that are off kilter due to something dumb I overlooked.

Huh, I just realized something. As of yesterday, I started this thread exactly 2 months ago. ( and I'm still not done ) Time flies, huh?

[RitchieMars]

It's hissing... AGAIN. Sounds like another HV leak somewhere around the flyback. Why me?