I've hit a bump repairing an early-60's Philco. It seems like there is enough info here that it should be evident where I need to look, but I'm not seeing it.
I have a raster with no video or snow, with bad v. linearity and, like a foldover about 1/4 of the way down the screen:
If I inject video at point B, the grid of the video output tube,
I get a clear, sharp, and completely geometric image with no foldover line, that is to say it's not just video that appears but the vertical sweep issues seem to disappear as well when a video signal is injected:
I have verified that the video detector is OK, or, at least checking like a germanium diode with a 2.65v drop one way and open the other.
I have tried an IF signal on the grid of the 2nd IF as well as the 1st IF tubes, with no visible effect (full disclosure my IF source is variable with a tiny analog meter to set the frequency so I'm pretty much throwing rocks in the dark, though sweeping up and down around where it
should be is giving me nothing at all).
Plate voltage on both IF tubes is about 25% high, but then so is the B+ - that 145V source at point 47 measures 182V. That 2nd IF cathode is right on the money at 1.5V.
All the resistance measurements for V1 and V2 according to Sams are pretty close.
To complicate things, when I put my meter probe on the plate of V2, the screen darkens quite a bit and the vertical foldover/linearity problem becomes more pronounced:
When I put my meter probe on pin 1 of L7, at the output of the detector, the screen goes black and the vertical shapes right up, looking pretty much like the crosshatch above but without the, um, crosshatch.
As I said, I feel like I should have enough information to know next steps, but I don't. It seems like the weird vertical problem should be a clue to the lack of video, given that it goes away when pretty much anything happens on the grid of the video output tube, including touching my meter probe to it.
I don't know enough about IF and RF to understand how my probe may be affecting the behavior of the circuit, especially on the plate of V2.
Can anyone point me in the right direction? (Edit: V1 and V2 are new)
Thanks.