W/G K7500 Blurry, Focus control doesn't do enough

uriahsky

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I have tried three different flybacks and they all show the same kind of thing. I can just barely adjust the focus but I am at the end of the POT turning radius. On the focus control on the flyback I have to crank it all the way to the left and it just about makes it look OK but I am worried that it will go a little out of focus over time and I won't be able to dial it in anymore. I did a cap kit on the chassis but it didn't really help. This is also the second tube I have tried.

I don't see any components between the flyback and the focus grid so there isn't anything I can change out??? Is there something else that affects the focus on this monitor? Has anyone resolved this type of thing? Any ideas.
Thanks
Russ
 
Tube was tested

I have a Sencore CR7000 and it tested very good in all of the tests and didn't need any type of rejuvenation. I also tried it on another tube and it was the same thing. I don't think it is the tube and this is the third used flyback I tried. All of the flybacks were used but I would think I would get some difference with the focus control when I swapped between them but in all of them I had to crank the focus all the way over. I even swapped neck boards and that made no difference. If there is nothing else between the flyback and the focus, then maybe I missed something. What about the B+. Could that affect the focus? The only other thing that came to mind was if the voltage going into the flyback was off and maybe that threw the focus off?
Thanks
Russ
 
what may or may not make a difference...

the flybacks that shipped with these, as well as the tubes as outlined, were all kinda garbage. while I think it's kinda unlikely for all 3 to be of the same condition, you have to consider that there's always a possibility when using used parts.

I suppose try a new flyback to see if that helps at all. I don't know if you left the monitor on long enough, but with a failing flyback it's possible to see drifting brightness and/or focus over a period of about 20 minutes from power-up.
 
If you have another neckboard, try swapping it on to see if it fixes itself. If so, I'll have further suggestions...
 
New flyback would be my next step too :) (My suspect is the HV resistors in the focus block, built into the flyback) All 3 were old and used and drifting up and up maybe

All the best
 
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