NOS K7500 is too dark, screen pot on flyback glued down

da66en

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NOS K7500 is too dark, screen pot on flyback glued down

Got one of those minty K7400s from Chad. This chassis is fresh out of the box, never been used.

When connected to my CRT the screen is too dark. Adjusting the brightness on the remote board isn't good enough. I can't adjust the screen on the flyback because it's glued down. Is there any particular reason why a sealed K7400 from the factory would have this pot glued down? Can I adjust this pot or should I leave it alone?

Is this perhaps a sign that my CRT is shot, or am I reading too much into this?

My previous chassis (K7100) worked and was bright, but it has blooming and hor size problems I could never fix - hence why I want to use this K7400.

Thanks,
Darren

EDIT: it's a K7400, not a K7500
 
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Well, first off a K7500 is not a replacement for a K7100. The K7500 is medium-res and the K7100 is standard-res. If you try to use a medium-res chassis on a standard-res yoke, it won't work properly, and picture will look really dark. Sometimes the sync or geometry will be off. Adjusting the brightness won't help much, as the brighter it gets the more washed out the pic will look.

BUT - if you want to pull the glue off and adjust the screen pot on the flyback, that's fine. It's put there to keep the factory setting from moving during shipment vibrations...
 
Well, first off a K7500 is not a replacement for a K7100. The K7500 is medium-res and the K7100 is standard-res. If you try to use a medium-res chassis on a standard-res yoke, it won't work properly, and picture will look really dark. Sometimes the sync or geometry will be off. Adjusting the brightness won't help much, as the brighter it gets the more washed out the pic will look.

Ooops - it's a K7400 not a K7500.

BUT - if you want to pull the glue off and adjust the screen pot on the flyback, that's fine. It's put there to keep the factory setting from moving during shipment vibrations...

Factory setting? Wouldn't that have to be adjusted with a particular CRT?
 
7400 ON A 7100.... HMM...

Get an xacto knife and start cutting at that glue. Mabye you can crank the brightness up enough to work but i have a nagging suspicion that there may be a chassis to tube/yoke mismatch going on, or it could be that tube is weak. DO you happen to own a rejuvenator ?
 
Ooops - it's a K7400 not a K7500.



Factory setting? Wouldn't that have to be adjusted with a particular CRT?

It was normally shipped with that CRT, but they made extra. Also, some probably got broken during shipment, and the unused chassis was kept. Remember that this wasn't made yesterday, so all the CRT's shipped with K7400's were new back then and this would have worked with all the new CRT's. Your CRT is not only NOT new, but the yoke wasn't designed for the k7400. So - expect some adjustment issues and hope you can make it good enough...

BTW - I don't know the details on these "minty" chassis from Chad, so I don't know if caps have been replaced or whether they are the originals. Despite what an ESR meter can tell you, caps age even when not used, and what tests good before going in the box doesn't always work after being bounced around in shipping....
 
you could try adjusting the sub contrast pot.
it's rite in front of where the remote board cable plugs into the main chassis.

Peace
Buffett
 
You guys a real downer. I was hoping for some encouraging words like "You can do it!" and "We believe in you!"

How do you know if the tube needs to be rejuvenated?
 
Something isn't right. Adjust pot on remote board, sub pot near the remote board connector or the flyback doesn't give me a good brightness. It looks too dull. So unless someone has some good suggestions, file this chassis as not compatible?
 
Is there any reason to not rejuvenate a CRT?

A rejuvenator doesn't only "rejuvenator" the tube. It's a tool with meters and settings. When hooked up to the tube, it (sort of) lets me see inside the vacuum sealed tube....it gives me an idea of what's going on with the internal electronics. This lets me know if the tube needs rejuvenated.

Edward
 
i know yours is a 7400. but i had a 7500 that did EXACTLY the same thing as yours is doing.

i replaced all the caps checked resisters and all kinds of parts, adjusted every knob on the thing, but could not get it to brighten up at all.

So what fixed it you ask:

low and behold it WAS the tube.

Got it rejuved (this was before i owned one) by a fellow KLOVER.

and it LIVES happily in my blitz cab looking bright and beautiful.

so you need to get the tube checked.
it could be that simple.

OH!!!!!! and keep it up you are doing a great job!!!!!!!

Peace
Buffett
 
Since rejuve's seem to be pretty cheap, going to try to find one in the area to borrow or buy one myself.

But I don't have high hopes that it's my problem - the CRT is plenty bright with the K7100, just not with the K7400. But K7100 has blooming, maybe because flyback on K7100 is way high to get brightness up?
 
dunno. A rejuve is a good tool to own just to TEST tubes with.. Thsat function alone is worth owning it. Right now, you could test that tube in 5 mins and have an answer as to if the tube is the issue or if its something else. Of course the other plus of a rejuve is that if you find the tube is borked, you can try to rejuvenate it and bring it back. It does not always work, but its a nice function nonetheless.


If you ever are going to be about an hour south near beloit lmk as i am in machesney park il and i own a rejuve...


One more dumb question, you have adjusted the color gains and cutoffs on the neckboard, right?
 
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dunno. A rejuve is a good tool to own just to TEST tubes with.. Thsat function alone is worth owning it. Right now, you could test that tube in 5 mins and have an answer as to if the tube is the issue or if its something else. Of course the other plus of a rejuve is that if you find the tube is borked, you can try to rejuvenate it and bring it back. It does not always work, but its a nice function nonetheless.


If you ever are going to be about an hour south near beloit lmk as i am in machesney park il and i own a rejuve...


One more dumb question, you have adjusted the color gains and cutoffs on the neckboard, right?

Before today I didn't know that a rejuve could be used as a testing device, so thanks to all of you guys for educating me. Cadillacman, you have a PM incoming.
 
replied to. You actually have to watch out what you get on feebay because some like from old sears technicians are "test only"the rejuve functions have been disabled.
 
Did you catch the part where like.. everyone has said you may have a yoke incompatibility? I mean I know its standard res too, but I personally never checked the resistances between a K7000 yoke and a K7400. Youre essentially doing some frankenstein shit here. A K7400 is not part of the same series as a K7000.

Your tube could be junk too. This is why you need a rejuvenator to rule out whether its the tube or not. Theres your words of encouragement: listen when people tell you stuff.
 
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