Dissecting a cathode ray tube television

Main Question or Discussion Point

I'm considering dissecting an old, color cathode ray tube television. Do cathode ray tube televisions have capicitors in them that could shock me?
 

Answers and Replies

turbo
Gold Member
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Please do not play around with electronics if you don't know what you're doing. I'm not going to give you any information regarding TVs because that is not a safe place for an amateur to start.
 
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Not to mention the large evacuated glass thingie the picture appears on... a very dangerous thing even when the tv is switched off & disconnected from the mains.
 
Not to mention the large evacuated glass thingie the picture appears on... a very dangerous thing even when the tv is switched off & disconnected from the mains.
Why would the glass screen of a tv be dangerous even when the tv is switch off and disconnected? Do you think it would be dangerous because it could break and cut someone?
 
Please do not play around with electronics if you don't know what you're doing. I'm not going to give you any information regarding TVs because that is not a safe place for an amateur to start.
What is a safe place for an amateur to start?
 
turbo
Gold Member
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What is a safe place for an amateur to start?
Start with battery-powered circuits that you can bread-board. Radio Shack has bread-board kits with components that you can learn from. Learn the functions of the components, how to read the values of those components from markings, how to measure the values using a digital multimeter, etc, etc. Before you delve into AC or high-voltage DC circuits, you MUST learn how to test and safely discharge capacitors. They can kill you.
 
Turbo,

What does bread board mean?
 
turbo
Gold Member
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A bread-board is a perforated plastic circuit board on which you can build circuits using discrete components.
 
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Why would the glass screen of a tv be dangerous even when the tv is switch off and disconnected? Do you think it would be dangerous because it could break and cut someone?
There is a vacuum inside the tube, so it could implode and send glass shards flying everywhere. Also there may be toxic chemicals.
 
In the tv show MacGyver, MacGyver once made a bomb out of the cathode ray tube of a tv, and that's what sparked my interest.
 
The capacitors in a crt are large enough to kill you and they can keep a charge for years after being plugged in.
 
berkeman
Mentor
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In the tv show MacGyver, MacGyver once made a bomb out of the cathode ray tube of a tv, and that's what sparked my interest.
Well there's a healthy interest in learning.... :rolleyes:

As others have said, please learn a LOT more before messing around with a TV or computer monitor. In addition to the large mechanical energy stored in the evacuated CRT itself, the high voltage circuit that charges up the CRT (the conductive coating on the faceplate is held at around +25kV with respect to the electron gun in the back/neck of the CRT), can hold a residual voltage of several kV when turned off. And that residual charge sticks around for an amazingly long time in some cases. Certainly several days (probably not years though).

There are also AC mains capacitors like after the input bridge rectifier, which can stay charged up to hundreds of volts for days as they leak down. Very unpleasant when brushing up against exposed leads (Quiz Question -- why do I know that? Ouch.).

Finally, there is no safe "ground" in television sets. They often use a "hot chassis" design, which means that if you do not use an isolation transformer in working with open TVs, you will either blow up your oscilloscope or electrocute yourself. Or both (now THAT would be a bad day, to have both happen....).

So a) start with more basic circuits to learn from, and b) don't make your learning aimed mostly at how to blow stuff up.
 
vincentm
Gold Member
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Why would the glass screen of a tv be dangerous even when the tv is switch off and disconnected? Do you think it would be dangerous because it could break and cut someone?
Because they still retain a charge, and pack quite a punch even when unplugged, don't do it.
 
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There is alot of chemicals inside a CRT, such as lead and phosphorous in form of a fine powder which if disturbed will disperse into the air.
 
Last edited by a moderator:
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I'm considering dissecting an old, color cathode ray tube television. Do cathode ray tube televisions have capicitors in them that could shock me?
You could get some damage playing with something like that, but you can also discharge capacitors with a resistor (~50-200k Ohmms value should be fine) connected to two wires.
 
NoTime
Science Advisor
Homework Helper
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Most new CRT circuits and power supplies have built in bleeder circuits which discharge the voltage fairly quickly.
As long as the bleeder circuits themselves are not broken which happens from time to time.

Older CRT implementations could hold a significant charge for months.
 
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DON'T DO IT! EXTREMELY DANGEROUS!

I have seen dangerous charges on CRT's that have been disconnected for a couple years.

Just don't do it.
 
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I'm considering dissecting an old, color cathode ray tube television. Do cathode ray tube televisions have capicitors in them that could shock me?
Heck, yeah they do! Experienced repairmen usually won't even touch one until it's been sitting unplugged for a week or more. There can definitely be enough charge in TV capacitors to kill you.
 

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