Hardware

Looking inside a CRT monitor

When we purchased our Apple IIc, it came already partially cracked open along with its monitor. Because it was pretty much useless otherwise, we thought it would be a good chance to tear apart and see what was inside of a CRT. Here's what you'll find.

When we purchased our Apple IIc, it came already partially cracked open along with its monitor. Because it was pretty much useless otherwise, we thought it would be a good chance to tear apart and see what was inside a CRT. Here's what you'll find.

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Where today flat-panel LCDs are the basic monitor of choice for computer systems, CRT monitors dominated for decades. Based on the same technology made to build TVs since the 1920s, CRTs have pretty much gone unchanged for 80 years. About the only difference you'll find between a computer monitor today and a TV from the 1950s is the solid state electronics today that make up the interface between the display tube and the tuner in the case of a TV or the VGA interface in the case of a monitor.

CRTs aren't the type of things you want to just crack open and look around inside. There are usually high-voltage capacitors that don't discharge for a long time. It's easy to get zapped if you're not careful.

When we got our Apple IIc for the Apple IIc Cracking Open Gallery, it came to us complete with an Apple IIc monitor. Both of them were damaged in transit. The monitor's case was cracked enough that it would have been unsafe to operate. What better opportunity to see what was inside a CRT.

So that's what we did.  Check out the Apple IIc  Monitor Cracking Open Gallery.

5 comments
mjd420nova
mjd420nova

The vacuum inside a CRT can be hazardous but is easily solved but not with a hammer and screwdriver, I've seen too many fracture and implode that way. A simple pair of wire cutters to clip off the nipple at the socket on the back is more effective and will not create the flying glass effect. Using a long screwdriver with alligator clip attached will effectively slide under the rubber cup on the anode connector and make removing the connector simple and grounds out the high voltage supply. In most cases, one shorting event isn't enough, as the charge can rebuild itself and catch many unaware. Use another clip to clip wire to short the anode socket to ground for at least a minute and also be sure the wire from the flyback transformer gets a lengthy shorting period too as the "doorknob" capacitor can rebuild charges that can be lethal to some.

TheChas
TheChas

Pictures 36 and 37 are of the deflection yoke and high voltage anode connection respectively. The deflection yoke does not help the electron beam get to the front of the CRT. The electron gun does that on it's own. The deflection yoke guides the electron beam as it traces up and down and across the screen to create the image. The high voltage anode (37) connection is where the 27,000 volts or so from the flyback transformer is connected to the CRT. The wire is thick because it takes a lot of insulation to keep 27,000 volts from shorting out. This is also the main point where people get zapped accidentally when they poke around in a CRT monitor or TV. Another source of danger in a CRT is the high vacuum inside the CRT. The face of a CRT is a lot thicker than the back or neck. So, it is a lot safer to rest a CRT on it's face. When the glass on a CRT is shattered, the CRT does not explode. The sudden loss of vacuum causes the CRT to implode in a violent manner. Back in the day, we made defective CRT's safe to dispose of be releasing the vacuum. We used a nail and hammer to carefully open the seal inside the high voltage connection. A large 27" CRT would hiss for several minutes while the pressure equalized. Chas

BALTHOR
BALTHOR

Somebody else got your new virus free computer.

John Sheesley - TechRepublic Pro
John Sheesley - TechRepublic Pro

Poorly worded, but that's essentially what I meant when I described the deflection yoke. Also, shame on me, I didn't have the technical term listed. As for the rest of the information, thanks for the additions!

w2ktechman
w2ktechman

I once worked in a TV/VCR shop, and scrap TV sets I would use a long (sheilded) screwdriver and a hammer to do the same. If there was a 'pop' and a hiss, it was done right