Philco 50-t1483 Focus problem

[Microtrol]

Tom,
the focus coil reads a couple ohms off but well within tolerances. The adjustment when its turned up will cause the screen to enlarge a bit but the focus does not get any better. After reading around here a bit I tried lowering the brightness to a minimum and set the contrast in a dark room and the picture is better but not great. Again the focus pot does shift it but it doesn't get any better. I saw from a few posts that if the CRT is gassey, this problem will occur but i guess my next question is that none of my crt testers show bad emission or shorts (beltron 8080 and a BK465), would they be able to detect the gassey condition?
When the brightness is turned up, the screen washes out and looks even worse, I have another 12lp4 and gonna try swapping it to see if this corrects some of this and if not will look into the focus system.

Thanks

[jeyurkon]

I think if the CRT were gassy enough to affect the focus that you would be able to see the blue glow of the beam. I have a test CRT that is gassy enough to see the beam, but it still has decent focus.

Did you look at Roger's thread? Checking to see if the focus coil leads are reversed sounds like a good idea.

How did the grid cutoff test of the 12LP4 fair with the BK465? If it's really low you might also be seeing the hollow cathode effect (I think that's what it's called) where the center of the cathode is dead and the emission is only from the edges, which wouldn't give you very good focus.

John

Originally Posted by Microtrol

Tom,
the focus coil reads a couple ohms off but well within tolerances. The adjustment when its turned up will cause the screen to enlarge a bit but the focus does not get any better. After reading around here a bit I tried lowering the brightness to a minimum and set the contrast in a dark room and the picture is better but not great. Again the focus pot does shift it but it doesn't get any better. I saw from a few posts that if the CRT is gassey, this problem will occur but i guess my next question is that none of my crt testers show bad emission or shorts (beltron 8080 and a BK465), would they be able to detect the gassey condition?
When the brightness is turned up, the screen washes out and looks even worse, I have another 12lp4 and gonna try swapping it to see if this corrects some of this and if not will look into the focus system.

Thanks