A question about discharging a tv

mr aize

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Built a discharging tool out of a screwdriver and a bit of speaker wire with a crocodile clip on the end, but I was wondering about where to attach the crocodile clip. Read up about it and everything i've read about says unplug the set and attach it to a grounded part of the chassis. My question though, is... If the set is unplugged then surely no part of the chassis is grounded since there's no path to earth down the lead? Would it not be better to attach it to something like a radiator, i.e. part of the central heating system, which is permanently connected to the earthing system of a house?
 
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Gonemad

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You can connect it to the dag wire.

Built a discharging tool out of a screwdriver and a bit of speaker wire with a crocodile clip on the end, but I was wondering about where to attach the crocodile clip. Read up about it and everything i've read about says unplug the set and attach it to a grounded part of the chassis. My question though, is... If the set is unplugged then surely no part of the chassis is grounded since there's no path to earth down the lead? Would it not be better to attach it to something like a radiator, i.e. part of the central heating system, which is permanently connected to the earthing system of a house?
 

NEO-GEO man

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Plug it in and leave the switch off so the metal parts of the chassis are common to ground, you want the current to take the path to ground, if you simply short it to the metal and its not connected to ground, all youll be doing is raising the potential touch voltage of the metal chassis.

As long as the switch is off, you will only have neutral and earth connected, active will be isolated. Neutral and earth are at the same potential in your electrical installation, and are connected to each other in the main switch board of your home via an MEN link, as well as numerous points along the supply side of the network.
 

mr aize

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Cheers mate, that's kinda what I figured. Was just a bit puzzled by various videos like this one http://www.youtube.com/watch?v=mV9Td8vAb0Y which say to unplug the monitor. Is that cause they don't have switches on plugs in the states or something? Just doesn't make sense to me as I know a little about electrical theory etc (i'm a domestic electrician by trade) an I couldn't figure out how it could work without the neutral/earth plugged in.
 
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mhkohne

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Cheers mate, that's kinda what I figured. Was just a bit puzzled by various videos like this one http://www.youtube.com/watch?v=mV9Td8vAb0Y which say to unplug the monitor. Is that cause they don't have switches on plugs in the states or something? Just doesn't make sense to me as I know a little about electrical theory etc (i'm a domestic electrician by trade) an I couldn't figure out how it could work without the neutral/earth plugged in.

Think of the tube of a monitor/tv as a capacitor. To discharge the capacitor, you don't need a path to earth ground, you need a path to the OTHER LEG of the capacitor. Now in the case of a monitor, the 'other leg' is usually tied to earth ground (and generally the metal framing of the monitor).

Now, as to leaving it plugged in: If you are sure that both hot & neutral are cut off by your switch, then leaving the earth ground connected between the monitor and the real world certainly won't hurt anything, but it's not required to safely discharge the monitor.
 

NEO-GEO man

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Think of the tube of a monitor/tv as a capacitor. To discharge the capacitor, you don't need a path to earth ground, you need a path to the OTHER LEG of the capacitor. Now in the case of a monitor, the 'other leg' is usually tied to earth ground (and generally the metal framing of the monitor).

Now, as to leaving it plugged in: If you are sure that both hot & neutral are cut off by your switch, then leaving the earth ground connected between the monitor and the real world certainly won't hurt anything, but it's not required to safely discharge the monitor.

Neutral is not switched in domestic outlets, and nor does it need to be. The voltage potential between neutral and earth is ZERO VOLTS. They are connected together in the switch board on any MEN system.

As for the capacitor theory, all well and good, but the other leg of the capacitor in this case is NOT the metal chassis, it is the cathode in the neck of the tube. Remember you dont need to touch both legs on a cap to get a boot from it, and in the case of a CRT, it is charged through the HV transformer, which is an isolation transformer, and hence, has no reference to earth. So touching either the anode OR the cathode may indeed cause a substantial electric shock as both will be at a different potential to earth. Discharging the anode will in this case be sufficient. This is not like a capacitor that has one leg connected to neutral.

Cheers mate, that's kinda what I figured. Was just a bit puzzled by various videos like this one http://www.youtube.com/watch?v=mV9Td8vAb0Y which say to unplug the monitor. Is that cause they don't have switches on plugs in the states or something? Just doesn't make sense to me as I know a little about electrical theory etc (i'm a domestic electrician by trade) an I couldn't figure out how it could work without the neutral/earth plugged in.
No problem, i figured you mustve had some electrical knowledge behind you. I would say that it may have something to do with the lack of an isolating switch on US socket outlets yes, and im not exactly sure how their protective earth system works over there either, largely cause i have no interest in it.

I am pretty sure the system you have over there is very much the same as the system we have here in Australia, being the MEN system, or multiple earth/neutral. Every installation has an earth stake driven into the ground connected to the main earth bar in the main switch board, the main neutral bar is also connected to the main earth bar via the MEN link, and serves to keep the neutral line at the same voltage potential as earth. The protective earth is there to carry current ONLY in a fault situation, and to provide effective operation of the circuit protective device ( be it a fuse, RCD, ELCB, RCBO, or MCB ).

In the case you want the protective earth system to bring the anode of the CRT down to earth potential, which will then make it safe to work on.
 

mr aize

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Cool, sounds pretty similar to the set up we've got here, not gonna go into it as not very interesting.
 

Xian Xi

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I discharged my TV when it was unplugged, did it 3 times to be sure and it was fine.
 

mhkohne

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Neutral is not switched in domestic outlets, and nor does it need to be. The voltage potential between neutral and earth is ZERO VOLTS. They are connected together in the switch board on any MEN system.

I see your point. My desire for a neutral cut-off is born of long experience with knuckleheads wiring outlets backwards (half the outlets in my house were wired backwards when I moved in). So I'm just over-paranoid there.
 

rcantor77

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Glad this topic cam up, been meaning to do this to my arcade monitor for a while so I can take off the board to replace some caps and give the thing a damn good clean.

Does it make a pop sound or is there a way to test that it had discharged ok..?

Anyone got a link to a 'decent' video on youtube...?

Someone also told me that you should not use the monitor for a while before you discharge it..? I it take that is rubbish then.
 

mr_b

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I was scared shitless about having to do this the first time. I've always unplugged my cab and clipped the alligator clip to the metal braid that goes around the monitor. Every time I've discharged the monitor. I've never heard a pop. I've also always taken the old pc repair rule of (unplug turn equipment on to discharge any juice). Now I don't know if a Monitor/TV will drain when you flip the switch, but I've done it every time and I've never heard a pop when discharging the monitor.
 

toricmedia

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Hi. Having worked on the wiring in my house and seen it first hand I never assume things are wired correctly. Ie. I have come across neutral and live crossed over.

With a single pole switch only the live is switched but, in my house this may actually be the neutral. You just need to he weary when doing things while still plugged in.

Having just discharged a monitor recently it also didn't make a sound, although it had been off for a couple of days.

Thanks.
 

300wins

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I was the same boat with mr_b that I was scared shitless too my first time too. Then my buddy BIGTIME showed me that there wasn't anything to be afraid of. I too use an alligator clip to the metal braid. And I have never once heard any pop or anything. I have probably done it over two dozen times now without any incident. I take precaution by inplugging everything first though.



I was scared shitless about having to do this the first time. I've always unplugged my cab and clipped the alligator clip to the metal braid that goes around the monitor. Every time I've discharged the monitor. I've never heard a pop. I've also always taken the old pc repair rule of (unplug turn equipment on to discharge any juice). Now I don't know if a Monitor/TV will drain when you flip the switch, but I've done it every time and I've never heard a pop when discharging the monitor.
 

gum_drops

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Same here, I wonder if the blast city monitor auto discharges.
 

NEO-GEO man

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I see your point. My desire for a neutral cut-off is born of long experience with knuckleheads wiring outlets backwards (half the outlets in my house were wired backwards when I moved in). So I'm just over-paranoid there.
This is EXACTLY why non trained persons shouldnt be doing electrical work, which im lead to believe happens in the USA all the time and there is no law to prevent it. There is very good reasons that it is not legal here to perform unlicenced electrical work, and the first reason is most people have no idea what they are doing or how it all really works.

Hi. Having worked on the wiring in my house and seen it first hand I never assume things are wired correctly. Ie. I have come across neutral and live crossed over.

With a single pole switch only the live is switched but, in my house this may actually be the neutral. You just need to he weary when doing things while still plugged in.

Having just discharged a monitor recently it also didn't make a sound, although it had been off for a couple of days.

Thanks.

Again the same reason as above, and i know that unlicenced electrical work still goes on here in Australia, but at least the fact its not legal is enough to stop most. I assume youre an electrician by trade as well?
 

clutch

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I've 'discharged' the Blast City monitors numerous times. Never heard so much as a pop. I think they auto-discharge. But that's not gonna keep me from sticking a screwdriver under that cap every time. :)
 

norton9478

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I don't use an alligator clip...

I use a terminal and screw it right into the frame.

Then I run a continuity test from the tip of the screwdriver to another point on the frame to make sure everything is connected right.

I do this both before and after I discharge the monitor.
 

rcantor77

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I always thought you got a pop when you discharged it, but obviously not.

Found this video on YouTube... seems quite a good one.
http://www.youtube.com/watch?v=bDAiLtTDuf4

I think I will make some space in my garage and give it go at the weekend, dying to get my other cab up and running again.
 
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NEO-GEO man

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Well ive removed and replaced numerous tubes in CRT video projectors, and never ever once have i discharged one. Never once got a shock either. The tubes in CRT projectors are obviously alot smaller, however they do run at a much higher voltage, usually anywhere from 34kV to 40kV depending on the brand of tube they use.

Ive pulled a few anode caps off TV tubes for various reasons, and never got any kind of shock from anything other than a SEGA Motorcross twin cab.
 

gum_drops

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You guys are making this too complicated. All you need is a good pair of rubber gloves and a bent coat hanger. If you are a safety nut you can double up on the gloves.
 

NEO-GEO man

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Rubber gloves WILL NOT insulate against 14kV. Dont kid yourself.
 
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