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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Taking Apart A Television (is this safe)?
Hi
Im planning to take apart an old cathode ray tube television I have. Television is an amazing device, invented by the great Philo Farnsworth when he was only twenty one years of age. Should I be careful for anything specific? Would the selenium be a problem? Chemicals? Thank You |
#2
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The CRT is the primary concern for two reasons: It can implode
sending chards of glass everywhere and it acts as a huge high-voltage capacitor. Do you plan to take the TV apart and reassemble/reuse it? If not, you might want to vent the CRT to eliminate the possibility of implosion. This can be done by breaking the glass nipple off the neck. Regarding the HV, even if the TV is broken and/or hasn't been used in years, there can be enough residual HV on the CRT to knock you on your butt. There is probably not enough to kill you but it's surprising what injuries can be sustained when you jerk your hand back after being zapped with 20KV. Most people use a long screwdriver to discharge the CRT. You'll probably note a fat red wire going from the flyback transformer to the bell (2nd anode) of the CRT. While holding the screwdriver shaft in contact with the metal chassis, work the tip under the rubber cap of the 2nd anode connector on the CRT. If there is a charge, you'll hear a "snap" as it is discharged through the screwdriver to the chassis ground. You won't feel any shock because you are being careful to keep that screwdriver in contact with the chassis the whole time. (Guess what happens if your screwdriver isn't contacting the chassis?) One note here... even after the CRT is discharged, it can and will build up a new residual charge - even if the TV is not turned on or even plugged in. So, discharge it again if you plan to put your hand anywhere near that 2nd anode connection on the CRT. The charge is in the CRT, not the red wire. Also, don't have any expensive electronics near the set when you discharge the CRT. There is a little EMP that is generated that can damage some devices. I've lost a few PC keyboards this way. As far as chemicals, I think you're OK. There may be cadmium in the phosphor but you're not going to mess with that. There is lead in the solder - try not to breath it and don't eat it. Wash your hands before eating. You mention selenium... does this set have an old selenium rectifier? It's probably not dangerious as long as you don't eat it. (I guess you can eat a little - RDA of selenium is 55 micrograms according to the national Academy of Sciences - seriously.) Good luck. On 30 Jan 2005 08:38:36 -0800, wrote: Hi Im planning to take apart an old cathode ray tube television I have. Television is an amazing device, invented by the great Philo Farnsworth when he was only twenty one years of age. Should I be careful for anything specific? Would the selenium be a problem? Chemicals? Thank You |
#3
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Television invented by Philo Farnsworth?
Are you re-writing history? wrote in message oups.com... Hi Im planning to take apart an old cathode ray tube television I have. Television is an amazing device, invented by the great Philo Farnsworth when he was only twenty one years of age. Should I be careful for anything specific? Would the selenium be a problem? Chemicals? Thank You |
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#5
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Most people use a long screwdriver to discharge the CRT. You'll
probably note a fat red wire going from the flyback transformer to the bell (2nd anode) of the CRT. While holding the screwdriver shaft in contact with the metal chassis, You are supposed to arc the anode lead to the DAG, not the chassis ground. One way is to use a wire with alligator clips, one on the screwdriver and another on the metal DAG braid usually wrapped around the back of the picture tube, and then gently insert the tip of the driver under the anode cap towards the connection point. You'll know when you've discharged it (if it was charged) when you hear a POP. It is recommended that you use a high value resistor in the ground path, though. - Reinhart |
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"LASERandDVDfan" wrote in message ... Most people use a long screwdriver to discharge the CRT. You'll probably note a fat red wire going from the flyback transformer to the bell (2nd anode) of the CRT. While holding the screwdriver shaft in contact with the metal chassis, You are supposed to arc the anode lead to the DAG, not the chassis ground. One way is to use a wire with alligator clips, one on the screwdriver and another on the metal DAG braid usually wrapped around the back of the picture tube, and then gently insert the tip of the driver under the anode cap towards the connection point. You'll know when you've discharged it (if it was charged) when you hear a POP. It is recommended that you use a high value resistor in the ground path, though. - Reinhart The DAG is connected right to the chassis ground in every set I've seen, so shorting to the metal frame if there is one is generally fine. Most TV's don't have much of a metal frame though so it's easier to clip the wire to the spring strap around the bell of the tube that contacts the dag. |
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Wow...Thanks guys. I didnt realize that I would have to take such precautionary measures. The television is a 1999 sony, I believe. It was struck by lightning and now the image is so tinted that the TV is not worth salvaging. I just wanted to take it apart, examine the components and learn. And yes, many people did indeed contribute to the great invention that is television; Vladimir Zworykin Paul Nipkow G.R Carey Jons Berzelius Baird Jenkins Philo Farnsworth We owe a great debt of gratitude to those men. |
#9
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How old is this TV? If it's old enough to contain tubes other than the CRT or a selenium rectifier it might be worth something as a collectible. Laughing. Seleniums went out of the picture long before tubes. |
#10
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Charles Schuler wrote: How old is this TV? If it's old enough to contain tubes other than the CRT or a selenium rectifier it might be worth something as a collectible. Laughing. Seleniums went out of the picture long before tubes. I have been working on color TVs since 1955 when I was doing some college work on color prototype sets, even before the RCA CTC-1 came out. To the best of my knowledge, no color set has ever been manufactured in the USA using selenium rectifiers. The current levels were too high and the selenium rectifiers got so hot that they were relegated to mostly B+W sets and to automobile battery chargers where they tended to be used with ventilation. The very early RCA - CTC-1 vintage sets used multiple 5U4s. One early CBS prototype set, non-rotating wheel, built right after the RCA NTSC format was approved, was a 2-cabinet affair. One cabinet was just for the power supplies, the other cabinet used a round 16" metal picture tube with a 12" flat color screen mounted inside the metal tube. It took days to get the set purity and convergence set up, and you didn't dare move the set once it was set up because the set was so sensitive. This was at the University of Florida - Gainesville. I graduated in 1957, and don't know what happened to that old CBS set. It generated enough heat that we couldn't run it more than a couple of hours except in the winter. No air-conditioning in the labs back in those ancient days. H. R. (Bob) Hofmann |
#11
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wrotesnip)yes, many people did indeed contribute to the great invention that is television; Vladimir Zworykin Paul Nipkow G.R Carey Jons Berzelius Baird Jenkins Philo Farnsworth If I recall correctly, Zworykin was responsible for the cathode ray tube, which Baird later attempted to use in experiments with the first TV signal transmission systems. But don't quote me on that! ;-) -Ben |
#12
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wrote in message oups.com... Wow...Thanks guys. I didnt realize that I would have to take such precautionary measures. The television is a 1999 sony, I believe. It was struck by lightning and now the image is so tinted that the TV is not worth salvaging. I just wanted to take it apart, examine the components and learn. And yes, many people did indeed contribute to the great invention that is television; Vladimir Zworykin Paul Nipkow G.R Carey Jons Berzelius Baird Jenkins Philo Farnsworth We owe a great debt of gratitude to those men. Try degaussing the tube, that might fix it right up. Sony makes a good set and that's a fairly new one. |
#13
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I just read all of these comments.
The only very dangerous thing you should be worried about, is if you accidently break the CRT. Other things to worry about is if there is any high voltage retained in the CRT anode, and if there are any dangrous voltages stored in the main capacitors. It is difficult over an email to describe procedures such as these, in a way that would be reliably safe for someone else of no experience to follow. Getting in to a TV set without the proper training and supervision is something that is not considered safe by any means. In service centers, they don't even like their experienced technicians to work on sets when alone, in case of an accident. If you want to learn something worth while about TV, take a structured electronics coarse, and then after you do a few years of studying, you may have enough basics to read some books to get an idea of what goes on in a TV set. Taking one apart will not really teach you more than how to take it apart, and maybe if you are lucky, you will learn about what a mild jolt can do to you. Find out from your local city hall about where to take the set for disposal. This is the safest for you, your family, and the environment. -- Greetings, Romeo E. Albert ============ wrote in message oups.com... Wow...Thanks guys. I didnt realize that I would have to take such precautionary measures. The television is a 1999 sony, I believe. It was struck by lightning and now the image is so tinted that the TV is not worth salvaging. I just wanted to take it apart, examine the components and learn. And yes, many people did indeed contribute to the great invention that is television; Vladimir Zworykin Paul Nipkow G.R Carey Jons Berzelius Baird Jenkins Philo Farnsworth We owe a great debt of gratitude to those men. |
#14
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"Jerry G." wrote in message ... I just read all of these comments. The only very dangerous thing you should be worried about, is if you accidently break the CRT. Other things to worry about is if there is any high voltage retained in the CRT anode, and if there are any dangrous voltages stored in the main capacitors. It is difficult over an email to describe procedures such as these, in a way that would be reliably safe for someone else of no experience to follow. Getting in to a TV set without the proper training and supervision is something that is not considered safe by any means. In service centers, they don't even like their experienced technicians to work on sets when alone, in case of an accident. If you want to learn something worth while about TV, take a structured electronics coarse, and then after you do a few years of studying, you may have enough basics to read some books to get an idea of what goes on in a TV set. Taking one apart will not really teach you more than how to take it apart, and maybe if you are lucky, you will learn about what a mild jolt can do to you. Find out from your local city hall about where to take the set for disposal. This is the safest for you, your family, and the environment. -- Really the best way to learn is by learning to fix them rather than just take them apart. Contrary to what some say, TV's are not terribly dangerous to work on, I'm completely self taught as I'm sure many of the professional techs here are. If I hadn't taken apart TV's to work on them I'd have never learned how in the first place. That said, read up on the safety first, there's no need to freak out and go overboard but it is important to know a few basic rules and have common sense when working on these things. Read the sci.electronics.repair faq first, then familiarize yourself with using your DMM, practice some soldering and desoldering, go out and find some broken TV's, then browse through the TV section of the FAQ again and dig in. Post here if you get stuck and keep at it, sooner or later you'll get the hang of it. |
#16
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Charles Schuler wrote:
How old is this TV? If it's old enough to contain tubes other than the CRT or a selenium rectifier it might be worth something as a collectible. Laughing. Seleniums went out of the picture long before tubes. I'm not sure how to parse that sentence. Seleniums disappeared before tubes disappeared, but there were certainly sets containing both. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
#17
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"CJT" wrote in message ... wrote: Wow...Thanks guys. I didnt realize that I would have to take such precautionary measures. The television is a 1999 sony, I believe. It was struck by lightning and now the image is so tinted that the TV is not worth salvaging. I just wanted to take it apart, examine the components and learn. And yes, many people did indeed contribute to the great invention that is television; Vladimir Zworykin Paul Nipkow G.R Carey Jons Berzelius Baird Jenkins Philo Farnsworth We owe a great debt of gratitude to those men. I seriously doubt a 1999 television will contain a selenium rectifier. It won't, or tubes, but that discussion was before we knew the age of the set. |
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