Philco roundie

[DaveWM]

hmmm the bias voltage at the HOT is only -30 should be -60 per sams, but the drive form looks right (shape and PP). there is a horz bias pot, adjusting it did nothing.

[DaveWM]

wow that focus coil was really smoked, burned to a crisp. I had a new one so in the process of replacing. I wonder if overloading the HOT could drive it into grid emissions, accounting for the -30 vs -60? There is no DC leaking as I checked the grid voltage with the HOT pulled, right around 0-1 VDC, per the DMM. If there was a leaking coupling cap I would expect to see B+ there, esp before the osc starts up.

[DaveWM]

well the new focus coil did the trick HV came right up and got a good raster.

tried a weak signal but could not get a horz lock, and could not seem to flop the horz lines. the pots are very very dirty, so not sure the horz pot was even working. I will pull the chassis and to a good cleaning of those and see if I can clear that up. There is a .47 cathode bypass cap on the horz AFC that is connected across the horz hold pot. If its one of those 200v jobs, then I would suspect it. Before I dig too deep I will scope the output from the sync sep to make sure I am getting a clean pulse as well. could also bee an AGC issue, I have had flaky pots do odd things to the noise invert and really goof things up, so that's why I like to look at the sync pulse before assuming anything.

Brightness and vert kept winking out as well do to dirty pots.

[DaveWM]

the set had its fly cage pulled off, and of course the fly looks like crap (but the cathode current is right where it should be). I wonder how often were flys replaced when the problem was somewhere else.

clearly there was no reason to pull the cage, the focus coil was very obviously the problem and it was not inside the cage. I did not even have to pull the chassis, just lay the set on its side, remove the two bolts from the bottom, and pull the chassis out a few inches to get at the coil. total replacement time was maybe 5 min.

[DaveWM]

fooled about with it some more, got a horz lock and vert lock. the vert is pretty stable, the horz is very touchy but I can indeed flop it, so my guess is the sync pulse is good (vert good) and will prob just replace the horz AFC diodes. they are easy to get at with the way the chassis is still pulled out from the focus coil fix. convergence is terrible, as is the purity, but I can see the color is demodulating. contrast seemed a bit weak, will bridge the video output cathode bypass cap (200uf) and see if that is the problem.

[ctc17]

The flyback is a lot of wire turns in a coil filled in a doughnut like was thing. Sometimes if it rotates to fast the hot will make the wax come all over the bottom. Then they will think its bad but its really the other thing with lots of coils around and Allen screw with a plastic thing like the one in the furnature at Ikea. Those ones come wiht the Allen driver in the box but this one has a plastic insert for your fingers not to shock your self. If the flyback is domesticated and tame you can remove the cage and let it out to play. The extra x-rays will help vasectomate like the TSA scanner at the airport. In the long run that will help save you money on pleasure babys that will require more tv sets in the house.