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determining crt type when it won't power up

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tipc

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Is it possible to truly tell whether a crt is green, amber, white, or color? Single color phosphors are usually pretty easy to spot I think (shine a flashlight on it). But what if you absolutely wanted to determine if a crt was (multi) color? IOW R, G, and B phosphors?
 
I had a look at a couple of my monitors, and you'd be able to tell a 15kHz RGB/CGA type monitor pretty easily by looking closely at the screen and noting an RGB phosphor pattern similar to that on a TV (for example, my PCjr monitor has long vertical stripes of red, green, and blue phosphors). A VGA monitor on the other hand has a phosphor pattern a bit too small to differentiate, and just looks grey, but you might be able to tell something with a magnifying glass.
 
Color ones are easy to spot. Like jmetal88 says, use a magnifying glass.

It usually isn't easy to tell what color monochrome ones are. Sometimes the glass is tinted, or there's a filter that will be green on a green CRT, for example. But, not always.
 
KC9UDX said:
Color ones are easy to spot. Like jmetal88 says, use a magnifying glass.

It usually isn't easy to tell what color monochrome ones are. Sometimes the glass is tinted, or there's a filter that will be green on a green CRT, for example. But, not always.
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well if the choices are rgb color or green, won't the green phosphors reflect green light when a flashlight is shined on it for a bit, then removed, in a dark room?

Could someone try for me please . . . none of my stuff is with me. I've done this of course. Would likely be difficult to determine a white phosphor monitor and an rgb by this method. But green should be easy to spot I would think.
 
My 5151 definitely shows green when I shine a torch at it.

In fact, I tried it just before... it hadn't been switched on for 3 months, and I could see the last thing it had displayed (XTree)! Does anyone know how on earth this could be the case?
 
It's called phosphor burn.

If you have a strong UV lamp, such as that in an EPROM eraser, take the jug into a very dark room. Expose the face of it to the UV light and then turn the lamp off and observe the afterglow. You should be able to clearly see the phosphor color.
 
Dark room and a camera flash works wonders for me.

A lot of the PC grade monochrome monitors had incredible phosphor persistence. The monitor on my Epson can keep glowing for well over a minute after you pull the plug. In a perfectly dark room and with a camera on manual shutter and a flash I've seen a glow for well after three minutes.
 
vwestlife said:
Not strange at all. CRTs were used as a form of computer memory:

http://en.wikipedia.org/wiki/Storage_tube
Click to expand...

Yes, but the phosphor persistence had nothing to do with that--in fact, there was no need for a phosphor at all--the effect is electrostatic. Storage tube displays are different matter--like a storage tube oscilloscope, the writing mechanism is different from a standard CRT.
 
NeXT said:
Dark room and a camera flash works wonders for me.

A lot of the PC grade monochrome monitors had incredible phosphor persistence. The monitor on my Epson can keep glowing for well over a minute after you pull the plug. In a perfectly dark room and with a camera on manual shutter and a flash I've seen a glow for well after three minutes.
Click to expand...

The fabled P39 long persistence phosphors. IBM 5151, Eagle/Northstar Dimension monitors. Absolutely devastating quality of monitors in those days, that unfortunately didn't didn't have the persistence to survive the high quality color monitors that came along.

Epson Equity? Cute little machines.
 
tipc said:
Is it possible to truly tell whether a crt is green, amber, white, or color? Single color phosphors are usually pretty easy to spot I think (shine a flashlight on it). But what if you absolutely wanted to determine if a crt was (multi) color? IOW R, G, and B phosphors?
Click to expand...

If all else fails, you could crack it open and take a look at the manufacturer's part number on the tube itself.
 
I tried the camera flash trick and it does work, although you'll need a powerful flash held right up to the CRT and viewed in a dark room to see the phosphor glow, and with a short-persistence-phosphor CRT it quickly fades away. If you still have one with good batteries, a 35mm film camera will have a far more powerful flash than the gnat-sneeze flash found on most modern digital cameras.
 
Any light bulb of sufficient output pointed at the face of the tube should have the same effect. 60W at 5 minutes to be sure, should work. Don't use fluourescent lamps as they persist also and the effect won't be as obvious. But, do this in a very dark room, close your eyes for a while to increase your luminence perception, then turn all the lights off and open your eyes.

It never occurred to me before because I never wondered what colour a nonworking CRT was, but I see this everytime I turn off all the lights by my oscilloscopes.
 
tipc said:
Is it possible to truly tell whether a crt is green, amber, white, or color? Single color phosphors are usually pretty easy to spot I think (shine a flashlight on it). But what if you absolutely wanted to determine if a crt was (multi) color? IOW R, G, and B phosphors?
Click to expand...

First look at the label on the tube it self, at the end of that number is the code for green/amber etc.
Just look at datasheets of the tube and there will be written the color of the tube.

MONO or COLOR is to be seen at the neck of the tube. That small glass tube at the end of the CRT.
If there is 1 system in it its a MONO, if you see tree round systems its a color tube.
Or also just type in the type CRT mentioned on the label on the tube it self.

Maurice
 
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