1949 Zenith Porthole Restoration

[Radiotronman]

Ok,

I changed the remaining three electrolytic canned capacitors and the power resistors and I was rewarded with a one inch line on the screen! So at least we know the flyback isn't gone. Now to figure out why I'm getting insufficient height. If I turn brightness up or down, the raster will disappear.....

[IsthmusTV]

Nice work! Have you tried carefully adjusting the ion trap?

You've come a long way and you're getting really close!

-Clark

[Radiotronman]

It didn't have an ion trap on the crt when I got it. I can try one from another set and see if there's any change. Thanks!

[bandersen]

If it doesn't have one and you see something on the screen, it doesn't need one. Probably an aluminized CRT like a 10FP4.

[IsthmusTV]

Originally Posted by bandersen

If it doesn't have one and you see something on the screen, it doesn't need one. Probably an aluminized CRT like a 10FP4.

Hmm. If it has a 12LP4 as stated in an earlier post, that would normally require a double field ion trap. Probably a rebuild with a straight gun in it.

Looks like your getting close!

-Clark

[damen]

Wow!! That looks great

[Radiotronman]

So I still only have 4000v at the second anode and can't find any obvious signs of why. Voltages at the horizontal output, damper and picture tube all test pretty close to the values listed in the schemstic.

[Radiotronman]

Finally made the molding that was missing around the side louveres. Still working on the flyback issue.

[Radiotronman]

Decided to take off the remaining flaking aquadag and spray on a new coat.

[Radiotronman]

Picture tube is now recoated!

[Radiotronman]

I'm wondering if I should try my zenith flyback replacement. This one cleaned up pretty good, but still wonder if it's weak? Do flybacks become weak or is it a situation where they either work at or not?

[Bill Cahill]

Looking at the picture of the flyback, it looks to me as if there is a burned spot on the hv donut. My guess is a short.

[bandersen]

Could be insufficient drive signal to the horizontal output tube. Do you have a scope ? Also I believe there is a 470K resistor on the second anode that may have gone way up in value. Could also be as simple as a weak 1B3 rectifier tube.

[Radiotronman]

I already replaced that 470k resistor that was inside the 1b3 tube socket. I also tested my 1b3 tube and it tests good on my tester. I have the horizontal drive control at it's max setting and get as high as 5000v, instead of 10k.

[Radiotronman]

I disconnected the doorknob cap, to see if it was shorted and pulling down the hv; but there was no change. I think I'm left with changing the flyback with a nos one a friend gave me.