Zenith 25LC20 chassis: Adjusting T14...HELP!!!!

[nasadowsk]

Ok, I've got my 25LC20 almost tuned up, but T14 is giving me a headache. I can't adjust it so there's drive to both demodulator tubes. I can get one or the other. I'm not sure the slugs in it are correct, so I might need to hunt down another one I guess. Any other ideas anyone? The book proceedure is worthless, here....

[DaveWM]

dont have that schematic, is that the one from the chroma band pass or the 3.58mhz osc?

[nasadowsk]

It's the one off the 3.58 osc, that injects the signal into the demod tubes.

Check out a copy of the schematic here:

https://www.flickr.com/photos/nasado...15950/sizes/o/

[DaveWM]

are you getting the 80v PP cw on the primary?

[nasadowsk]

Yeah. I might be slightly off frequency (I haven't measured that), but it's a good, strong, and reliable signal on the primary.

[DaveWM]

My guess on the cores of the secondary is they should be tuned for max CW with the core apart from each other (top nearest top bottom nearest bottom).
I would tune with the scope on them. if one of them seems to not respond to a nice peak then maybe its a cap inside the can?

[andy]

...

[nasadowsk]

Looks like I'll have to check the caps and everything - I can get CW on one side or CW on the other, but not both at the same time.

[DaveWM]

are both the slugs moving? that really seems odd that you can adj but only get on set of coils in the secondary at a time to work.

[nasadowsk]

Yeah both slugs are moving. What really odd is out of the set, I can adjust it to work right, but in the set...no dice.

I have 25LC30 chassis as a parts set. Anyone know if the chroma injection transformers are the same for both? I *think* they are, I'm not sure though.

[DaveWM]

did you try applying stress to the can? I would get it working outside the chassis then install and try pushing around the sides of the can. I have not opened the cans but maybe its one of those mica caps in the base and somehow with the chassis out something is getting flex just enough to make it work.

[nasadowsk]

I pulled the one from the parts chassis, it's the same part #. I'll install that one and try again this week...

[DaveWM]

any update? unsolved mystery's drive me nutz.

[nasadowsk]

It's gonna be a few days, I'm royally tied up at work Also, the horizontal section is acting up so I'll need to check that out, too. Should be easy fix though, most likely a loose wire or such (the set's horizontal was perfect until i moved the chassis, so it's something stupid)

with the 'new' T14 in place, I expect to at least see something color. Also might replace the osc coil cause it's jammed up...