Philco 49-1240 horizontal (?) problem

[teevee]

I suspect you're hearing the horizontal starting/stopping from the problem induced by the vertical section. Again, the scope will prove this out.

[old_coot88]

Phil,
Before disconnecting the fly for continuity checks, just for the heck of it, check the HV secondary and see if it `might' be open DC-wise.
It's doubtful there's anything wrong with the primary windings since the sweep width and boost appear good.

[Phil Nelson]

OK, here is the LV power supply schematic and the remainder of the HV circuitry (my set has two 1B3GT in doubler configuration, not one as shown there).

http://antiqueradio.org/art/Philco49...ySchematic.jpg

The HV secondary is supposed to be 2.5 ohms and I measure 2.6, so that seems OK.

Pulling the caps from the 6BG6 HOT and 1B3GT rectifier, I measure 134.6 ohms on the top half of the flyback primary (should be 240 ohms) and 35.8 ohms on the bottom half (should be 40 ohms). Not so close, but I can reserve judgment for the moment.

Referring to the p-s schematic, I put the scope on two points: the output side of choke L101, which supplies ~160vdc from the 7Z4 LV rectifier, and the output side of choke L100, which supplies ~320vdc from the 5U4G LV rectifier.

The 160vdc supply looks smooth and stable.

The 320vdc supply is jittery, and the jitters change (along with the ticking sound) as you turn the vertical hold control, seen in these two photos:





So, it's sounding plausible that vertical noise is leaking into that 320vdc line. Referring to the sweep schematic, I see that one lead (red) of the vertical output transformer connects to that line. Possibly I could disconnect that lead and then see if the jitters go away . . . .

Phil Nelson

[Electronic M]

Originally Posted by Phil Nelson

Grr. Using a listening tube, it seems the ticking (arcing) sound originates in the flyback. I don't own a flyback tester, but I suppose I can disconnect it and check the resistance of the windings.

Phil Nelson

Don't you own one of the B&K 1076/1077 analyst series and don't they act as a flyback tester among other things?

[Phil Nelson]

Sure enough, the Kiver book says it can check for leakage and shorted turns. Can't hurt to try it out.

Phil Nelson

[bandersen]

I went through my Riders and there are only two pages specific to the 49-1240 code 123. The rest they say is covered by the 49-1240 code 121 in Vol. 2.

I took a couple quick pictures of the two pages in Vol. 4 and the schematic in Vol. 2 and uploaded them here.

Let me know if the stuff I posted is what you need. There's about 50 pages of info in Vol. 2. I'm can scan it all for you, but it might take a couple days.

I also found this image of the control area which perfectly matches the channel plate on my 49-1040. Does your set have channel #1 ?

[Phil Nelson]

Thanks, Bob. That schematic looks like the Philco schematic that I got from Cliff, with the addition of a bunch of test points (A, B, etc.). If those refer to scope waveforms, they would be good to have, but let me digest this material for a couple of days before you spend a lot of time scanning. I am already struggling to retain my sanity with two sets of docs (Sams & Philco) both marked up and cross-referenced with part numbers from the other set. If I add a third set and try to cross-reference those printouts to the others, the world might explode.

I keep thinking that I'm only about half an hour away from whipping this mutt into watchable condition, but that's probably a fantasy. I should just slow down and try to learn something

My tuner plate looks like the one pictured -- an eight-position tuner including Channel 1.

Phil Nelson

[teevee]

If you want to temporarily disable the vertical, just pull the vertical output tube. Be sure to turn down the brightness first. Looking at the scope, can't tell much without knowing the sensitivity (volts/div) it is set for.

[Phil Nelson]

Pulling that tube sounds easy. The volts/div was set to 2 volts/cm.

Thanks,

Phil Nelson

[Phil Nelson]

Originally Posted by Electronic M

Don't you own one of the B&K 1076/1077 analyst series and don't they act as a flyback tester among other things?

Well, if my 1077B is accurate, my flyback failed the shorted turns test with flying colors

Here, I'm checking the topmost winding on the flyback, which connects between the plate lead of the 6BG6 HOT and the plate lead of the first 1B3GT rectifier. The resistance of this winding is supposed to be 240 ohms; I measure 134.6 ohms.

Perhaps Moyer has a sub.

Phil Nelson

[wa2ise]

Originally Posted by Phil Nelson

Well, if my 1077B is accurate, my flyback failed the shorted turns test with flying colors The resistance of this winding is supposed to be 240 ohms; I measure 134.6 ohms.

Perhaps Moyer has a sub.

from an earlier post:
Grr. Using a listening tube, it seems the ticking (arcing) sound originates in the flyback.

I'd think that that much of shorting (almost half that winding) would kill or drastically reduce the horizontal width, and drastically reduce the very high voltage feeding the CRT. The manufacturer may have had (after the info publication) thicker wire used in that winding, making the resistance read lower.

Some corona dope might take care of the arcing you were hearing.

[teevee]

If the flyback was shorted, you'd have low HV and boost. Assuming a x10 probe, you've got 20v p-p on that B+ line, try pulling the vertical output tube, (brightness turned fully down) and scope the line again. Another quick and dirty check would be to set the scope for "line" sync, and adjust the vertical hold. If the scope pattern walks, it's caused by the vertical. C102 and C104 would be the prime suspects here.

[Electronic M]

My EICO 944's manual recomends pulling the HV rect. tube and other stuff connected to the fly as it can cause a false bad reading. Perhaps the B&K is sensitive to that as well...

[bandersen]

Good point. Also, maybe you have a known good flyback lying around you could try testing with the 1077 ? Just to make sure it's working properly.

[miniman82]

I have read that most ringers are so sensitive that the filament winding will cause a false 'bad' reading if the tube is left in, pulling the tubes seems logical.