Open G2 or red herring?

[6502]

I have a 17DRP4 CRT (Philco Predicta original) that’s testing bad, it’s showing an open G2. Using B&K 440 to do the test. The tester is fine, as I also have a known working 21EAP4 CRT (Philco Predicta original) to compare and is not showing open G2.

The CRT showing open G2 looks good though. Both G2 pins are solid in the glass and the welds inside the neck look good. Is there some secret to the 17” Predicta CRT that would cause it to show open when it’s not? I’m questioning the test that says it’s a bad CRT because I have a video of this TV showing vertical collapsed raster. Would an open G2 still show a horizontal line?

I don’t think it’s caused by low emission because it has at least enough emission to show a good G1.

[bandersen]

Yes, it is caused by low emission. The G1 bulb will often light up before the G2 bulb. How long did you run it in the tester? Let it cook 15-30 minutes and see if the G2 bulb starts lighting up.

I've never, ever encounter an actual open G2.

[Tube TV]

You could lightly tap on the CRT neck with a piece of wood or a plastic handle screwdriver and see if it changes the open condition.

Vertical loss will be in the vertical circuit. Old capacitors, failed couplets, and The Predicta's weak tube sockets.

Just looking at the CRT pinout and you could check for continuity with a multimeter between pins 2 and 6 as they're both G2 to confirm open.

[6502]

I’m pretty familiar with all the work involved in getting a Predicta functioning reliably. I’m mostly interested in tracking down how the previous owner (antique hoarder lady) got light on the screen when she plugged it in. Would that be possible with an open G2? I also see zero ohms between pins 2 and 6. I know there are two other welds that could be broken that this continuity test does not check. But open G2 just seems so unlikely to actually be open.

I’ve had it on the tester at 2.68V for about an hour now. No change in the G2 light. Although, I do see about 1mm of deflection on the meter when I switch to emissions test. Since the tester says both lights out can be caused by bad emission, I figured one light out would mean there should be enough emission to light both.

I’ve got a Seventeener I can take a CRT from, I just want to make sure this one is actually bad before changing it.

Edit: And I know how to fix vertical problems in a TV, I know how to fix TVs, I’ve restored several. I didn’t mention the vertical collapse because I wanted to know what is causing it, i mentioned it to demonstrate that the previous owner had light on the screen. Sorry for the confusion

[6502]

It’s definitely bad emission, thanks for the responses. I hit it with the rejuvenate button and it came up a little bit. Now I get to change the CRT.

[bandersen]

No, an open G2 would not result in collapsed vertical. If G2 was open somehow, I don't think the CRT would work at all. It's normally aaround 400 volts and helps form the electron beam.

It is very, very likely a failed vertical linearity control. You can bridge it with a 2 watts resistor around 470-1.5 K if it is open. The linearity will likely be off, but it will restore vertical deflection.

[6502]

I guess I should also add a note to my tester manual about only the center indicator being half lighted can be an indication of no emission.