Philco 49-1240 horizontal (?) problem

[Phil Nelson]

Here's a new one on me. Looks like a strong wind is blowin' at the top of the screen!



Haven't had time to investigate causes yet. Just finished recapping and I'm taking a break for the evening.

It's almost like the vertical linearity is blowing up in the top couple of lines -- and the horizontal is flaking out, too. Despite what you might think at first glance, the whole image is stable.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[bandersen]

I've seen an effect like that on other sets. The culprit was the free running horizontal oscillator being so far off, it took that long for it to lock every frame. Is there a hor. oscillator frequency adjustment on this chassis ? If so, try giving it a tweak.

[miniman82]

Looks like horizontal tearing, if the picture is stable though it's probably just horiz AFC doing it's job. Do the horiz alignment procedure, if you already haven't.

[Phil Nelson]

We hear and obey. I haven't done any of that good stuff yet. It just seemed funny to have a picture that's so wrong, yet so stable.

Later,

Phil Nelson

[ChrisW6ATV]

The stability may be unique to the crosshatch pattern; normal video may not stay locked in. It looks like a nice bright, sharp picture, though. Nice going!

[Phil Nelson]

Just for kicks, I had also tried it with rabbit ears and the in-home modulator signal, which is weaker than the pattern generator signal. The horizontal behavior was much the same.

I'll haul out the Sams manual tomorrow and find all of the adjusters. I've been avoiding the Sams because it's not accurate for this model, but the Philco docs (athough accurate) only amount to a schematic and change/version notes.

Phil Nelson

[bandersen]

I think I have the Riders service info for it. Chassis 49-1240 code 123 & 124 are covered in Vol #4. I can take a look over the weekend if that would help.

[Phil Nelson]

Sure, that would be great. The more docs the better.

I just looked at the Sams horizontal adjustment procedure, which looks thorough and logical. Except that it uses three adjusters -- locking trimmer, etc. -- which this model does not have. (I peeked underneath to make sure they hadn't been moved to other locations. Simply not there.)

Tweaking the horizontal frequency coil did fix the windblown tearing, but the locking range is awfully narrow. I guess it's just not the world's most sophisticated TV, which is fine. I can still work through the sweep sections and try to bring everything up to spec.

Phil "they can't all be DuMonts" Nelson

[teevee]

I'd be scoping the B+ sources, looking for ripple and noise, most likely coming from the Vertical sweep retrace.. Jack Darr had written something like this up in one of his articles, a capacitor with a high power factor was the culprit, as I recall..

[Phil Nelson]

Yah, I may find all kinds of ugly stuff when I hook up a scope. All I've done so far is recap it, so I am just beginning the project.

Speaking of noise and retrace, if you turn the brightness & contrast far enough to show the classic slanted retrace lines in the top, you also see this squiggle in the center, which seems to trail down from the tip of the lowest retrace line.



Kind of arty looking, but I guess I should get rid of it eventually.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Tom Albrecht]

I have a hunch that funny squiggle will go away when the other problem gets cured. Must be occurring when the horizontal oscillator goes out of lock or something.

[wa2ise]

I'd look at the sync stripper and the sync separater circuits. Weak tube, leaky caps, drifted resistor could do it.

[teevee]

Those lines look like the horizontal momentarily quit at the beginning of the vertical retrace.. The fact that the problem is solidly locked to the vertical makes me suspect you'll see a pretty sizable vertical sweep induced ripple on one of the supply lines..

[Phil Nelson]

Just returned from a little family vacation, so I haven't gotten any farther with this. Here's the Philco sweep schematic for what it's worth:

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

I'm hearing a rapid ticking from the chassis, seems about vertical speed. The HV cage has been cleaned and shows no signs of past arcing. No signs of arcing anywhere, in fact. I hope this does not mean a vertical transformer is funky . . . .

Tomorrow, maybe I can locate my favorite listening tube and try to locate the ticking source. Will fire up the scope, as well.

Again, I have replaced all paper & electrolytic caps, plus C508, C516 and C517 in this schematic. I measure 327vdc on the 320v line.

Phil Nelson

[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