Mighty Monarch of The Air

[vts1134]

OK, maybe I found it! I was looking over C61 and C62 again to make sure they are installed correctly. C62 is indeed connected to +255v so all ok there. However, I am 99.9% sure C61 is MISSING! I will be especially sure this is the case if some one can speculate that a missing C61 would cause my glowing V18 problem.

This is also further reinforced by the fact that I had a cap with same value as C61 left over when I did the original recapping.

[VintagePC]

That could well do it!

Considering C61 is part of what comes out of the 1x2 cap -> through a transformer.

That means without C61, your flyback won't operate properly.

I'd connect it in the same way as C62 - using the optional 255V connection.

[vts1134]

Originally Posted by VintagePC

That could well do it!

Considering C61 is part of what comes out of the 1x2 cap -> through a transformer.

That means without C61, your flyback won't operate properly.

I'd connect it in the same way as C62 - using the optional 255V connection.

I would say the optional 255V connection is the way to go. Every thing else I've seen on the schematics have been in the optional dotted line configuration. I'll give the set a second and third look over to make triple sure that it is not in place and if it's not we'll see how it goes.

[old_coot88]

Originally Posted by VintagePC

That could well do it!

Considering C61 is part of what comes out of the 1x2 cap -> through a transformer.

That means without C61, your flyback won't operate properly.

I'd connect it in the same way as C62 - using the optional 255V connection.

If C61 was indeed missing, it'll be interesting to see what happens when he replaces it, since it is the bypass/'filter' for the bootstrapped (B boost) voltage. Since the vertical oscillator is supplied from B boost, the absence of C61 was probably introducing some wonkiness into the vertical waveform too.

What still puzzles me is- he was drawing a healthy 'air arc' off the plate connector of the 1X2. Assuming the replacement 1X2 is good, there should definitely be adequate HV coming out of it.. assuming there is no short to ground. One remaining possibility is that the second 1X2 is gassy. So one question- is the 1X2 getting hot after a few minutes of running? If it's hot, like too hot to touch, it would indicate the tube's gassy (even though it might still test good on a tester).

[vts1134]

Originally Posted by old_coot88

One remaining possibility is that the second 1X2 is gassy. So one question- is the 1X2 getting hot after a few minutes of running? If it's hot, like too hot to touch, it would indicate the tube's gassy (even though it might still test good on a tester).

I've only had the set on for seconds after noticing the problem so I don't know if the 1X2 is hot to the touch. I could test this theory if you think it's ok to leave the set powered up for that long.

[VintagePC]

It should be all right, (and I'm sure you know this) but don't run it unattended. (and replace C61 before you do fire it up!)

I like to run things through a power bar so I have a kill switch on hand that's not near/on the set, just in case. Then, keep watching and listening for any funny business and kill it if anything else starts acting weird. Keep a good eye on the flyback and kill the power if it starts to drip wax!

I should add that gassy tubes usually have a blue-violet flickering glow to them, which is in the _space_ inside the tube... What it looks like you have (and you can confirm this, since cameras don't usually do fluorescent colours justice) is a pure, deep blue coming from the inner layer of glass itself- that's entirely the fluorescent emission of the glass from being bombarded with high-energy electrons.

There's a couple of videos on YouTube (heh) if you search "gassy tubes" that will help you distinguish between the two.

[Phil Nelson]

Yah, some tubes can glow pure blue and work fine. I have observed this in a couple of sets.

Purple, not so good. The photo shows a 5U4G rectifier in my RCA T-100 just before it failed completely. Definitely purple rather than blue. There was nothing wrong with the TV, that old tube just gave up the ghost.

Phil Nelson

[vts1134]

I guess .1% wins this time. I found C61. It is a .05 instead of a .035 though. It was one of the black beauties and didn't have it's rating on it. It had the same marking bands as two other black beauties that were .05 though.

A few youtube searches on gassy tubes and I think this is what I have. The last two posts came in after I did the test so didn't have a chance to read the "don't do that" warning. The set was still only on for less than a minute.
http://www.flickr.com/photos/23097242@N03/5873904324/
This will help make it a little easier to see what the tube is doing. The video is of the new tube. The old tube does close to the same thing, just not nearly as much blue glow. I suppose #3 could be the charm.

[miniman82]

Originally Posted by Phil Nelson

The photo shows a 5U4G rectifier in my RCA T-100 just before it failed completely. Definitely purple rather than blue.

Damn, that thing is TOASTY!


http://www.youtube.com/watch?v=x7KK7bXJV2c

[old_coot88]

Originally Posted by vts1134

I've only had the set on for seconds after noticing the problem so I don't know if the 1X2 is hot to the touch. I could test this theory if you think it's ok to leave the set powered up for that long.

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.

[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.