Mighty Monarch of The Air

[vts1134]

Originally Posted by old_coot88

Umm.. considering the rarity and irreplacibility of that flyback, and since you haven't already run it for more than a few seconds in the fault state, please hold off on this test.
Rather (after replacing C61), do the 'air arc' test again. It will confirm whether the fly's putting out without loading it down.

Now, if the fly's putting out, install the 1X2 with the plate cap connected, and remove the doorknob. This will avoid loading the flyback (in case the tube is gassy). If the tube is good, the HV should come up and light the CRT. If the 1X2 is gassy, it may fry the 470K resistor (R89) in series with the HV lead. R89 is thus "sacrificial" and takes the load otherwise borne by the flyback with a gassy 1X2. Much easier to replace a resistor than the flyback.

Ok tests ran, here are the results. Fly is air arcing away. Door knob removed and HV going right to the picture tube. I want to rewind a bit to before. Miniman82 first suggested removing the doorknob cap and firing the set up to see if that solved the problem. The doorknob cap is secured to the base of the rectifier through a screw in the base to the top of the cap. On my first test I removed the screw. On this test I removed the screw and MADE SURE that the base was not in contact with the cap at all. Different result. The tube did not glow or crackle at all this time. Unfortunately a new arc has developed. It is between the flyback and the filament winding for the rectifier. I've indicated where it is with the white arrows below. It is not constant, and only happened 8 or so times total with all the tests I have done tonight. It seems that Miniman82 might have put his money in the right place and the doorknob is toast. It is not shorted to ground but it could be toast. A new doorknob might be the answer. I don't know what to do about the sparking flyback though.

[VintagePC]

Most people here will coat the flyback with a "sensor-safe" silicone product (regular silicone produces ammonia or acetic acid as it cures, which corrodes copper). That will likely kill the arcing. A few wraps of PVC electrical tape might work in a pinch for testing until you can get the right stuff.

[miniman82]

At this point, I'd recomment replacing the filament winding for the rectifier and the doorknob cap. I often find filament windings have degraded insulation, and that's never a good thing around HV.

[vts1134]

Got a good supplier for a 500pf 20,000v door knob capacitor?

[VintagePC]

Digi-key has a few... for example:
http://search.digikey.com/scripts/Dk...me=445-3890-ND
http://search.digikey.com/scripts/Dk...me=445-2235-ND


... but they won't be cheap :S

[old_coot88]

Well sunnava gun, so it was the doorknob all along, and now the filament winding is popping through. Some kind soul oughta send him a hunk of HV wire to replace that with, along with a doorknob.

[vts1134]

So as I sit here and ponder I can't help but think that the door knob cap ISN'T shorted to ground. If that cap was shorted to ground it would certainly account for our problem, but could just a leaky cap cause our problem? If not could it be the ground side of the cap some how isn't grounded? Or some other problem other than the cap itself being bad. I just know that some times in my work when I think I've found the answer from trouble shooting I just end up "fixing" things that aren't broken and still not finding the real problem.

[old_coot88]

OK, did the CRT light up with a raster after you removed the doorknob? If so, it would pretty well prove the doorknob was at fault. Probably arcing internally since it measured open circuit on your ohms test.

Earlier you mentioned a "new arc" that's developed. I (probably erroneously) interpreted it to mean there's a hole in the insulation of the filament winding that's allowing a DC arc. That would be evinced by a loud, sharp snapping sound. If instead the "arc" is a bluish, lightly hissing corona discharge from the 'tire' to the filament loop, you may be able to insulate it with some silicone. Is it possible to move the filament loop further down on the frame, away from the 'tire'?