EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Alex Eisenhut on February 12, 2016, 01:33:12 am
-
So I scored a nice little 9" NEC CRT monitor. It must have had a tough life, the tube is off-center relative to the bezel. So what mechanical things should I watch for when trying to re-align it?
Is it really as simple as loosening some bolts, re-centering the tube and tightening it? The implosion protection is just a tension band around the face of the tube, right? And all it does is "focus" the implosion to avoid glass flying everywhere? There's nothing inherent about the protection that avoids implosions in the first place?
Ie, there's nothing about the bezel that does the protection as well?
-
Most all CRTs made in the last 40 years have integral implosion protection. The way the glass is cast, it is very thick and strong on the screen side (this is also for X-ray protection; it is doped with heavy metals). If the tube breaks, the screen remains intact and glass fragments fly out the back side around the neck. You can hammer on the screen and all that happens is that it chips slightly. Hammer on the neck and it snaps right off.
The greatest danger when moving the tube is that the neck is not properly supported. Be careful about any boards that sit on it, that could pull it against your intended motion.
-
I once had an old logic analyzer and wondered why there were small brown spots on the screen, turned out there was a piece of polycarbonate sheet stuck onto the front with clear silicone adhesive and the mold spores had been busy whilst it was in storage.
-
So I scored a nice little 9" NEC CRT monitor. It must have had a tough life, the tube is off-center relative to the bezel. So what mechanical things should I watch for when trying to re-align it?
Is it really as simple as loosening some bolts, re-centering the tube and tightening it? The implosion protection is just a tension band around the face of the tube, right? And all it does is "focus" the implosion to avoid glass flying everywhere? There's nothing inherent about the protection that avoids implosions in the first place?
Ie, there's nothing about the bezel that does the protection as well?
The metal ring the tube bolts to the front of the case is part of the implosion protection, fixed securely into the glass.
Typical CRT alignment components consist of small fixed magnets (little more than flexible fridge magnets), a set of rings you can rotate, and the deflection coils themselves.
First check for any signed of things that used to be attached to the tube/coil with silicon, this could indicate the location of missing magnets.
Triple check you understand which way to loosen any metal C clamp rings, to avoid crushing the tube.
-
I don't want to align the color purity, just the tube itself mechanically because it sits at an angle. I doubt very much that NEC shipped it like that in 1987!
I've worked with scope CRTs, not so much TVs, I wanted to ask to be sure before I end up on the evening news.
-
I once had an old logic analyzer and wondered why there were small brown spots on the screen, turned out there was a piece of polycarbonate sheet stuck onto the front with clear silicone adhesive and the mold spores had been busy whilst it was in storage.
The adhesive is usually polyvinyl alcohol and it oxidizes over time, not from mold. Mold on glass is very distinctive and grows in long, transparent needles.
-
I don't want to align the color purity, just the tube itself mechanically because it sits at an angle. I doubt very much that NEC shipped it like that in 1987!
I've worked with scope CRTs, not so much TVs, I wanted to ask to be sure before I end up on the evening news.
Your chances of injury from an imploding 9" tube are about the same as flying to the moon on gossamer wings.
Tens of thousands of Techs changed hundreds of thousands of such (& very much larger) tubes over tens of years without incident.
Tubes are usually fitted with four mounting "ears".
The front panel usually has four threaded "studs" sticking out of it.
You fasten the tube in place with four hex nuts.
Just loosen these nuts enough that you can move the tube---the holes in the ears have enough "wiggle"room for you to get the tube level.
Hint:Find where there is a horizontal line across the display,& with a felt tip pen,draw a straight line across the tube face following the display line (Yes,Virginia,you can draw lines on a tube face.).
It is a lot easier getting the tube level when the monitor is off,as you don't have to worry about putting your fingers on "hot" bits while you are concentrating on the screen.