The proper way to discharge electricity from a flat screen before working on it.

[Nola_Gal]

Hi guys, I've fixed a few TVs already with the power supply problem by taking the DM board out and replacing the capacitors. However, the TVs I've worked on have all been sitting for over a month, & discharging the electricity wasn't such an issue. I found another good buy, a 50" mangavox flat screen for $75 with the same issue, but since I don't know when it was turned on last (and I'm not the kind of person who enjoys sadistic high voltage shocks)... I was hoping someone in this forum could give me a tried & true method of discharging any dangerous voltage from the set. Any simple tools or household items I could use to do this before I start working on it? I'm not going to go tinkering around with anything else until I know it's safe.

Thank you!

[goontron]

Re: The proper way to discharge electricity from a flat screen before working on it.

You dont have to discharge LCD tv, they dont hold charge. However the large caps do, but they have discharge resistors so they discharge in a matter of hours.

Btw. With valve radio consoles the chassies is live

[Nola_Gal]

Re: The proper way to discharge electricity from a flat screen before working on it.

You dont have to discharge LCD tv, they dont hold charge. However the large caps do, but they have discharge resistors so they discharge in a matter of hours.

Btw. With valve radio consoles the chassies is live

Thanks. I've looked at some other flat screen repair forums that say things to the contrary. It's just not something I want to dick around with if there's a chance that it can shock you!

[goontron]

Re: The proper way to discharge electricity from a flat screen before working on it.

Thanks. I've looked at some other flat screen repair forums that say things to the contrary. It's just not something I want to dick around with if there's a chance that it can shock you!

Maby with plasma because of their voltage recovery circut, but not lcd.

Gah, i hate typing on a blackberry!

[Nola_Gal]

Re: The proper way to discharge electricity from a flat screen before working on it.

I hear ya. iPads aren't the best for typing either! So, I have one more question for you then, because I want to learn... What would you do in the case of a plasma tv?

I got into this because my old boss was giving away all the 37" flat screens in the bar that were having trouble turning on. I said "Sure, I'll take one!" I dig projects. I got one, and so did my friend Mike, who can barely work a stove. I fixed both of those & then bought and flipped another. What a simple fix for a $300 tv!

Got another one for free off of Craigslist. A Mitsubishi 55" projection screen (never again) they weigh about 200#. Figured that one out as well & sold for $100, but it was a huge pain in the ass. That's about what I have in the way of experience. I'd like to learn a lot more.
This is a great forum!

[tom66]

Re: The proper way to discharge electricity from a flat screen before working on it.

Maby with plasma because of their voltage recovery circut, but not lcd.

This is wrong, and dangerous advice. LCD TV power supplies can how just as much, if not more charge than a plasma TV power supply. The energy recovery circuit in a plasma is irrelevant; the capacitance is insignificant (<10uF) but on the power supply several hundred uF is usually present. I've had an LCD TV power supply sit all weekend with 160V still across the 450V cap. I learned painfully why to always discharge the cap.

To discharge it, the safe method is a 100 ohm 10W wirewound resistor. However, I've had good luck with just shorting cap terminals with a screwdriver. Can make a big spark and risk damage if you short the wrong parts though.

[JonathanAnon]

Re: The proper way to discharge electricity from a flat screen before working on it.

I have a bulb that I use to discharge the main filter capacitor. After discharging, I like to check the voltage across the capacitor as well, just to be absolutely sure that there is no charge left in it.

No matter what the circuit is powering, it is always a good idea to check for charge.. It only takes a couple of seconds

[Nola_Gal]

Re: The proper way to discharge electricity from a flat screen before working on it.

I've never discharged capacitors before, and searching the Internet hasn't really recovered much in the way of tutorials with visuals. I'm not brave enough to do the screwdriver method. It doesn't sound like a safe move for a novice like myself! But I'll get one of those resistors and give it a shot. Just so I have this straight, between the advice on badcaps & other info I've dug up.... Start to finish.

Tv is unplugged of course... I want to take the DM board out & flip it over after noting where the larger capacitors are. Then maybe hot glue the middle of the bleed resistor to something like a non conductive stick. Test the caps on an ohm meter, and discharge the ones holding more than 10v with my DIY bleed resistor. I'm aware that there are two large caps on the DM board. Probably the first two I need to be concerned with. After the 10v or higher capacitors & the big 2 are bled, is there anything else I need to worry about before I start to unsolder the 4 probable trouble makers?

[jamesbo]

Re: The proper way to discharge electricity from a flat screen before working on it.

You want to test the caps with a voltmeter. If the cap has a charge it will pop your ohmmeter's fuse or the meter itself, if it a cheap one.

[senz_90]

Re: The proper way to discharge electricity from a flat screen before working on it.

This is wrong, and dangerous advice. LCD TV power supplies can how just as much, if not more charge than a plasma TV power supply. The energy recovery circuit in a plasma is irrelevant; the capacitance is insignificant (<10uF) but on the power supply several hundred uF is usually present. I've had an LCD TV power supply sit all weekend with 160V still across the 450V cap. I learned painfully why to always discharge the cap.

To discharge it, the safe method is a 100 ohm 10W wirewound resistor. However, I've had good luck with just shorting cap terminals with a screwdriver. Can make a big spark and risk damage if you short the wrong parts though.

i have test shorting cap with screwdriver and it makes a spark that risk the screwdriver, but it give a little fun seeing that spark lol

[retiredcaps]

Re: The proper way to discharge electricity from a flat screen before working on it.

This is wrong, and dangerous advice.

It totally agree. While it is likely that the caps are discharged in modern consumer devices, it is not guaranteed.

I've had an LCD TV power supply sit all weekend with 160V still across the 450V cap. I learned painfully why to always discharge the cap.

I mentioned this before in several posts, but I have LG 22 inch monitor made in 2009 that will not discharge the large capacitor on its own after unplugging the device. If I leave it off and unplugged overnight, the large filter capacitor still holds 165V DC as verified by my Fluke multimeter.

In countries with 220V AC, that will be over 300V DC stored up in the capacitor!

I always check the voltage across the large filter capacitor before doing any work on the board. You can minimize the shock hazard by shorting out the larger capacitor with the resistor tom66 mentioned. I don't use the screw driver method.

[retiredcaps]

Re: The proper way to discharge electricity from a flat screen before working on it.

Norcal715 makes excellent and competent repair videos. You can see his 1500 ohm 10W resistor for discharging capacitors at 14:30 into the video.

http://www.youtube.com/watch?v=LjpGKaBt8hg

Note the above is just an example specific to one TV, but the idea and concept is the same.

He has used the same resistor in other videos, but I spent 15 minutes looking for the above and it is 1:45AM in the morning, so I'm done.

[JonathanAnon]

Re: The proper way to discharge electricity from a flat screen before working on it.

That's a picture of my discharge bulb..

[domas]

Re: The proper way to discharge electricity from a flat screen before working on it.

you hold the clamps with your bare fingers, right?

[goontron]

Re: The proper way to discharge electricity from a flat screen before working on it.

This is wrong, and dangerous advice. LCD TV power supplies can how just as much, if not more charge than a plasma TV power supply. The energy recovery circuit in a plasma is irrelevant; the capacitance is insignificant (<10uF) but on the power supply several hundred uF is usually present. I've had an LCD TV power supply sit all weekend with 160V still across the 450V cap. I learned painfully why to always discharge the cap.

To discharge it, the safe method is a 100 ohm 10W wirewound resistor. However, I've had good luck with just shorting cap terminals with a screwdriver. Can make a big spark and risk damage if you short the wrong parts though.

Ok, sorry. Im used to valve radios where the filter cap has a habit of discharging on the valve heaters and motor start/run caps that have bleeders.

[eccerr0r]

Re: The proper way to discharge electricity from a flat screen before working on it.

Were those old vacuum tube radios with live chassis (like the AA5) listed by UL or did this issue predate UL standards?

I wonder if anyone has gotten electrocuted by these radios before from normal use?

[goontron]

Re: The proper way to discharge electricity from a flat screen before working on it.

Were those old vacuum tube radios with live chassis (like the AA5) listed by UL or did this issue predate UL standards?

I wonder if anyone has gotten electrocuted by these radios before from normal use?

they are UL because of the fact that most are put inside of a non conductive cabinet like bakelite or wood plus the fact that some that don't predate UL have the secondary HV 375v DC + at the chassis.
but yes some do predate UL like my coronado, but to answer your question, the live chassis issue (if you call it that) predates UL, but UL didn't take notice for a long time.

[budm]

Re: The proper way to discharge electricity from a flat screen before working on it.

Old Fender tubes amps with two-prong cord are know to give you good shocks.

[senz_90]

Re: The proper way to discharge electricity from a flat screen before working on it.

That's a picture of my discharge bulb..

what wattage of the bulb? voltage? where the clamps rubber? forget to attach it? you will makes a contact with caps before it has charged.

[Behemot]

Re: The proper way to discharge electricity from a flat screen before working on it.

[QUOTE=goontron;375567]However the large caps do, but they have discharge resistors so they discharge in a matter of hours.]/QUOTE]

Matter of minutes actually. Those without resistors will discharge in matter of hours.