Soldering a Broken TV

Huh?

You're "very experienced in electronics and soldering" yet you don't know whether something is an FET or a triac?

Michael

Fix it that way. You don't have the skill set to do more.

Just lay some steel wool or tinsel around where you will be working and it will short out any voltage.

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Clyde Crashcup

I don't want to stick my head in between the high-voltage electronics and the CRT to see it more closely.

You dont need to discharge anything to do some soldering . The charge is held up under that big suction cup on the picture tube . Simply turn the set off and wait a few minutes for the filter capacitors to discharge by themselves , turn the board over then solder . In some cases when you walk up to a tv and touch metal parts you may get a static zap just like you do from the car door or door knob in your house .

That "big suction cup" has a wire extending from it to the HV section. Touching any bare section of that wire (although there shouldn't be any), or of the parts in the HV section to which it's attached, can give you a big surprise.

The picture tube itself holds the charge.

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That sounds like a recipe for problems later, when bits of steel wool left behind cause further shorts. Besides, putting steel wool on a board containing capacitors that aren't fully discharged already can discharge them through inappropriate paths.

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Responses like this are not constructive and downright dangerous.

Simply leave the TV off overnight. That should discharge any capacitors that would affect soldering on the mainboard. The only possible remaining charge may be on the CRT anode but that only goes to the flyback and you should not need to disconnect it. And, that will almost certainly be discharged by then in any case.

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In nearly all CRT TVs and monitors less tha 30 years old, it goes directly into the flyback and bare sections would be extermely unlikely.

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Unless the ground to the outside of the kine is disconnected. Not a good thing to touch if you are standing on the ledge of a second floor window.

Just get in there and solder it, if the set has been unplugged for a few days there's no risk.

I'm not sure I'd want to test it out this way, but in principle, if the ground only were disconnected after the set was turned off, there would be no voltage between it and ground.

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True, but when it is run that way and you just turned it off to twist the yoke . . . . .

I think a lot of the reponses so far have been attempts at humour. Possibly because you say youre very experienced yet dont know how to discharge a psu cap or the tube eht. No, you cant rely on them to self discharge over a day or so. Since youre experienced, figure it out.

NT

He made his skill level clear and the best advice for him is to not try.

Fix it that way. You don't have the skill set to do more.

HeHeHe... If it's run with the CRT ground disconnected, that's a different story. :)

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snipped-for-privacy@care2.com wrote in news: snipped-for-privacy@k70g2000cwa.googlegroups.com:

Go to the library. Get an older copy of the Radio Amateur's Handbook. It should show you how to make a tool consisting of a wire, a wooden dowel, and a resistor, that can be used to safely discharge high voltage capacitors.

These devices were called 'crowbars' because that is what they essentially were, a crowbar with a heavy wire that connected it to ground.

The operator would turn off the power, hang the crowbar on the high voltage line, grounding it, and work on the equipment, secure and safe. IF someone accidently turned on the power without removing the crowbar, it would blow fuses.

Nowdays, a circuit that shorts the output of a power supply to ground in case of overvoltage output of the supply is called a 'crowbar' circuit, for reasons that should now be clear.

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You are describing a "Shorting Stick" which is a safe way to discharge a HV power supply to service the equipment. It was also used in broadcast transmitters, in case the safety interlocks failed. A crowbar is not current limited, it is a fail safe shutdown circuit, and you can expect damage if it is triggered.

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Michael A. Terrell
Central Florida

discharging CRT skill easily learnt

NT