I've seen much worse, try cleaning a smoker's set. bleck.

Dang. After playing for a while, I heard arcing and the picture went nuts. I quickly powered down, then tried again in a few minutes with room dark and the HV cage open. After the set warmed up fully, I saw a two-inch spark shoot from the side of the flyback to the cage body.

There is freshly melted wax below the flyback.

Is it worth trying to recoat it with RTV, or should I assume it's shorted and look for a replacement?

Phil Nelson

Maybe there's a little too much current thru the flyback? That could melt some wax. And make for excessive HV? IIRC backing off on the drive may help, but the service notes should say what the current should be set to. I think you don't have a short in the flyback, or else the set wouldn't work as well as we see in the pictures, unless it got bad after the arcing. Some RTV should help, overcoating the existing wax "tire" on the high voltage secondary. But I'd check for carbon traces that may have formed in the wax.

Oh, I'm sure you cleaned inside there, so cobwebs and such should be gone.

It wasn't really dirty inside the cage, but I cleaned in there anyway. This set has no drive adjuster and the Sams manual says nothing about drive. I posted a link to the schematic earlier in this thread.

Phil Nelson

Here's the victim.

http://antiqueradio.org/art/PhilcoF4626MFlybackMelt.jpg

http://antiqueradio.org/art/PhilcoF4626MFlybackWax.jpg

Some of the layers under the doughnut had melted and sagged down so that you could just flick them off with a fingernail.

Should I try to melt off the old wax before recoating with RTV? Seems like I should at least reflow it with a heat gun so that it doesn't have big cracks.

The arc came out the side of the doughnut as seen in the second photo, going to the side of the cage. A very healthy spark! I'm not sure whether it came from the big crack seen in the first photo, or possibly from the nib where the rectifier lead enters the coil, since I only saw it for an instant.

If the cause of overheating is excessive HV, I'm not sure how to change that other than by modifying component values, as the set lacks a drive adjuster. After I noticed the vertical (drive?) line on the screen, I replaced the two 5% resistors (R83, R84) connected to the HOT input grid; both had drifted more than 20%.

My initial HV reading was a little low, about 14KV rather than the 16KV-18KV given in the schematic. That was before I recapped the sweep board and replaced a few resistors to address a vertical linearity problem. I hadn't tested the HV after that.

Unless someone has a better idea, I guess I'll recoat it, fire up the set again, and see what happens . . . .

Phil Nelson

Phil,
When it arced, was an RF arc (ie., hissy and sizzly sounding)? Or was it a loud, sharp "SNAP!"? If the latter, it is most likely rectified HV arcing through a pinhole in the 1B3 filament loop insulation.
Re. the drive line, did it change at all with the contrast setting?
Bill(oc)

Ouch! If that RTV doesn't do the trick, let us know the part numbers from SAMS. I just came across a box of 30 NOS Halldorson horizontal outputs and yokes, 1968 stock. There's a small chance.

Great job on getting the set going.

Kevin

The sound seemed more like a constant sizzling and the spark was a bright blue constant stream. I just cleaned the 1B3 filament loop and didn't see any gaping holes, although I suppose a tiny needle hole would be hard to spot.

The line definitely was minimized when I changed contrast & brightness to make the background truly black, although I'm not sure if that was due to the contrast setting alone.

Phil Nelson

Yeah, that would definitely be coming from the 'tire' itself, not from the 1B3 filament loop which would register as a loud SNAP or a staccato series of snaps.

that thing is toast, sorry bro.

Phil, have you ohmed the flyback from HO plate cap the HV plate cap to see if it is still continuous? What is the Philco and cross part numbers for the flyback from Sams?

No continuity between the 1B3 rectifier cap and 6DQ6 HOT cap. Bad sign, I guess.

The Philco part number from Sams & the transformer frame is 32-8799-1. No equivalent numbers are listed in the other columns for Holldorson, etc.

Phil Nelson

Crosses to Thordarson Fly 265.

Kevin

Hmm. Looking more closely, I see that the wire from the coil to the HOT cap is actually two very thin wires, and one of them is broken where it comes out of the coil. From that broken end back to the 1B3 rectifier cap I measure 541 ohms. The schematic seems to indicate 530 ohms between those points.

I wonder if it's worth trying to fix that break. I'm not good at soldering hair-thin wires, but if I had to replace the flyback, there would be some of that, anyhow.

Phil Nelson

Was that 541 ohms between the break and the 1B3, or you mean 541 ohms from the break to the HOT? 541 is close enough to 530.

Worth a try. Oh, and be sure that the new glob of solder has no pointy ends, but is rounded. Pointy ends may produce corona.

IIRC, solder iron heat and molten solder should burn off the enamel coating on the wire, if so, no need to scrape it.