Need advice about WEIRD k4900 symptom....please help!

Vectorman

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Guys,

Here's a new one for me. What do you think is causing this?

Monitor has been capped.

Thanks!
 

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You've got the wrong chassis for the yoke that's on your tube. Swap out the chassis.

Ah ha! That is very possible - I took a spare chassis off the shelf because the one on this monitor has blown up and burned a hole clear through the chassis board. I'll grab a different one off the shelf. Thanks!!! Will report the results later...
 
Well, I put a different k4900 chassis on the tube and it worked perfectly. I guess this doesn't prove whether the errant chassis would work right on the proper yoke. But I'll just take your word for it and keep trying it on other 4900s until I find one with a compatible yoke. Thanks again.
 
Well, I put a different k4900 chassis on the tube and it worked perfectly. I guess this doesn't prove whether the errant chassis would work right on the proper yoke. But I'll just take your word for it and keep trying it on other 4900s until I find one with a compatible yoke. Thanks again.


Count the potentiometers at the edge of the chassis, then pair it up with the proper yoke.
The 3 pot chassis uses Yoke 2021111201 (and 2021111194).
The 4 and 5 pot chassis use Yoke 2021111208 (and 2021111258 or 2021111264).

Screenshot 2025-08-25 at 9.12.46 AM.png
 
Count the potentiometers at the edge of the chassis, then pair it up with the proper yoke.
The 3 pot chassis uses Yoke 2021111201 (and 2021111194).
The 4 and 5 pot chassis use Yoke 2021111208 (and 2021111258 or 2021111264).

View attachment 842071
Wow...this is really helpful. Thanks! I appreciate the guidance. I've always kind of been confused by what seems to be a lot of different styles of 4900 chassis.

Thanks,
John
 
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