Dark Corner in Kortek CRT

[TalkingOctopus]

I replaced the monitor of my New Astro City with a Kortek (aka Betson Imperial) because the original monitor had scratches and burn in.  The monitor is mounted vertically.  The bottom right corner is a lot darker than the rest of the screen.  It looks like it needs degaussing, but degauss doesn't help.  I moved the arcade around to a different location, but that didn't help either.  Any ideas how to get rid of the dark corner?

To make the Kortek fit in the New Astro City, I had to swap the mounting frame with the original monitor.  Some tall and large metal things (heat sinks?) exist on the PCB near the dark corner.  Is it possible I mounted the monitor's PCB too close to the tube, causing this issue?

Last question, what programs or images do you use to calibrate CRT monitors? 

Thanks for the help!

[Rigby]

Please show a picture.  Some corner darkness can be cured with a cap kit, apparently, but a picture would help us diagnose it.

[TalkingOctopus]

Maybe dark corner is not the best description.  The corner changes its color depending the color displayed.  The corner is black for white, red for blue, green for red and blue for green.  The issue goes away when I tilt the arcade.

Here's an image of the corner where I mounted the PCB.  Is it too close?



Thanks for taking a look at this.

[Rickn]

The issue is related to magnetism! Keep in mind, the monitor was likely built and tested in the normal Horizontal mode... you have now changed it to vertical/Portrait mount.

A good degaussing may help, but the best fix is to re-adjust the purity rings.

Few simpler band aides... if the monitor has a "Rotation" control, try that other wise a small magnet in the bad corner.

Good Luck! 

[rCadeGaming]

Yeah try to find the service manual and perform the purity and convergence adjustments.

If you can get XP 32 displayed on that thing, search for the nokia monitor test software.  If not, let me know.  I can give you some images from it.

[Pixelhugger]

I'm pretty sure that's typical of the Betson monitor if brightness adjustment is set really high. I've had this issue on mine and ll it took was reducing brightness a little and it disappeared. Others have had to do the same. I don't think the monitor is intended to have the brightness cranked way up... Give it a try.

[MonMotha]

I don't think the monitor is intended to have the brightness cranked way up... Give it a try.

Indeed they are not.  Doesn't stop them from shipping them that way, of course.  "Brighter is better" after all!

The brightness (black level) probably needs turned down, but the contrast will affect this more, if there's going to be a setting like that that affects this.

It does look like just a purity issue probably caused, as Rick said, by it being rotated.  Some monitors will "dome" due to heating of the shadow mask.  This is caused by them being cranked up WAAAAAY too high.  The Makvisions are commonly shipped in this state, but the Betson/Korteks don't seem to do it as badly if at all, even at the default "cranked" settings.

[TalkingOctopus]

Thank you for the replies.  Unfortunately, lowering the brightness and contrast settings have no effect.  I have each setting at 80 (out of 100). 

I've studied the purity ring adjustment, and I'm going to give it a try when I have a chance. 

[Rickn]

Not recommended as a novice!

I can do the whole adjustment in about 60 seconds, but I have done a few thousand.

Check around to see if you can find local a magnetic like a fridge would v
have to hold the door closed.... go to the dump if need be.

Now stick that magnet on the bottom corner about 2 inches from the yoke. You may have to rotate it to correct the purity issue, then secure it with tape.

Good luck

Rick

[TalkingOctopus]

Not recommended as a novice!

Why not?  Am I more likely to make it worse? 

I watched some videos and the adjustment didn't look too difficult.  As part of this hobby, I'd like to learn how to make these types of adjustments.

[adder]

can u provide a not so close up picture of how your degauss coil goes around the back of the picture tube (it looks sort of bent in a non-standard way?)   maybe repositioning the coil is all you need to do.   eg. see pic below... try to get the coil very close/touching the glass if possible.  of course just incase you are not aware, any adjustment you make, you will need to wait for the tv to completely cool down before retrying, as the degauss circuit only functions from a cold start

[ed12]

look this is simple
puirty rings are sealed >note the word sealed<
rickn explained it to u...dam well listen to him
take a small magnet and go to the offending side
once u get it right >purity< all else will fall in
tape the magnet there
this is not a big ass magnet..just a small fridge magnet will do the job..
as i can see from your reply
u do understand u are working around 28kv ? if not hence the novice term
if so just slide the mag until u see it come out >spot<
u c the yoke will come free or basilcy lose the geormatey due to age heat etc
and to play with it willy nilly is just  plain stupied,plus if u break the putirey ring
ears u are in for a hole new can of work u just do not want

ed

[TalkingOctopus]

Thanks all.  I couldn't get the magnet to work so I did carefully adjust the purity rings.  It took me a lot long than 60 seconds, but I was able to fix the issue.  The purity rings were not sealed, but they were locked.  After loosening the lock a tiny amount, it was easy to adjust the rings.

[ed12]

congrads
most are sealed and will break

ed

[rCadeGaming]

Not recommended as a novice!

Why not?  Am I more likely to make it worse?

Yeah, not really helpful.  As long as you know how not to shock yourself, and be careful not to break anything, people need to try new things to learn.  It's not like it's easy to find a local tech that still works on CRT's to do it for you.

Also, carefully cleaning off whatever is used to seal the disc magnets isn't impossible.  Sometimes it's just white silicone sealant.  Other times you'll need to pull the yoke and clean and separate things very carefully.

any adjustment you make, you will need to wait for the tv to completely cool down before retrying, as the degauss circuit only functions from a cold start

Sounds like you need a handheld degaussing coil.

[TalkingOctopus]

With the right magnets, I think the magnet recommendation would work.  However, I couldn't find a location for the magnet that fixed the corner without disrupting another part of the screen.  Perhaps my magnet was too strong.