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Old 12-26-2004, 02:54 PM   #1
willawake
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Default Messing around inside CRT monitors - danger considerations

One guy posted this on dsl reports, i advised him to post here but he didnt. Can you give him some advice before he frys himself.

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I wanna know the dangers of taking apart crt monitors, I do it all the time for cleaning (air cleaning), trying not to touch anything inside. I know that the monitor can produce upto 30,000volts, but how many amps?

Can someone provide a picture of the dangerous part of the monitor, and what kind of contact it actually takes to get a shock from it (it requires actual contact and is not enough power to just jump out at you? )

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anyway here is the link or just post here and i will transfer it :

http://www.dslreports.com/forum/rema...5410~mode=flat
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Old 01-01-2005, 09:50 PM   #2
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Disclaimer (to be kept with this message): I avoid touching monitors whenever possible. I am not an expert. If anyone fries themselves, it was probably doing something worthy of a darwin award (like cleaning a monitor), and I am not responsible.

The most dangerous parts (aside from line connected parts) are the flyback, flyback lead, "suction cup", and the tube's anode terminal. It isn't so much the current of the flyback that's dangerous (though it most certainly is), it's the charge stored in the aquadag capacitor.

The inside and outside of the crt glass is covered in a thin film of conductive material ('dag), with the inside connected to the anode terminal and the outside to ground. This forms the capacitor used to filter the HV anode supply, and can store quite a bit of charge, for days (or more) even with the unit unplugged.

In addition to the HV dangers, moderately high voltages (300v or less) can be found all over virtually every circuit board in a modern monitor, and are NOT line isolated. Most don't even have a discrete power supply, and use the flyback to generate the ~100v horizontal drive voltage, etc, with random high voltages being found even in the middle of logic circuitry. The power supply capacitors usually don't store charge nearly as long as a tube with a failed bleeder resistor, and pulling the power cord with the monitor on discharges most of them, but the same precautions should be taken when near the PCBs as one would take with a switchmode power supply. Don't forget that many heat sinks have line voltage (or higher) on them!

If the monitor is unplugged, the anode cup left connected, and nothing touched, you're probably not too likely to die. Don't touch the circuit boards or the components on them, don't fidget with the anode lead, and under absolutely no circumstances whatsoever remove the anode cup. And, of course, follow standard line-connected safety precautions... only one hand on anything metal at a time, etc.

I think the SER FAQ (repairfaq.org IIRC) has a section on this; it's probably much more complete (and likely more accurate too...)


As an unrelated note, keep in mind that compressed air nozzles can build up a static charge, causing damage to the monitor. Are you sure your monitors really need dusting?


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Old 01-03-2005, 12:45 AM   #3
willawake
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thanks for that great info, i sent it to the guy. I agree that air cleaning inside a crt is pretty unnecessary and dumb. a noob hospital visit is not going to be worth it.
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Old 01-07-2005, 09:32 AM   #4
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If you must remove the anode wire, discharge the CRT first!!

If you have no idea how to discharge it, DO NOT take the back off your monitor!! Most newer monitor CRT's will discharge themselves when you remove power, but if there's a fault in the flyback or horiz circuitry, this function may not be working. I've been repairing monitors and televisions for years, and have knocked the hell out of myself a time or two.... It's NOT fun! If you're not experienced, or have no clue what you're doing don't even think about trying it!!

Motherboards are all low-voltage devices, nothing on a motherboard is going to shock you. PSU's and monitors are a totally different world though!
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Old 01-07-2005, 01:21 PM   #5
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wish i could have learnt crt repair, got one sony g200 dead, one 15" sony trinitron fading picture and now black only, and one sony 17" trinitron which has problems starting each day (my main office screen) needs several pushes of the button and removals of the power cord to get going, dont know if i should leave it on all the time maybe.

can you see a picture, hello Sony......, whilst all the utter crap in the office shamrock etc whatever crap was released in the 80s we have it and it is still working fine so will not be replaced as per management, the sonys are the ones to fault out.

having decimated the budget in one rackmount cabinet, guess i will be bringing the $70 AOC second monitor from home to use in the office. gotta find a good CRT tech in Greece. since sony screwed me for replacement of a captive vga cable on the only working 15" in the office i will not be going back.

TC : your comments are correct and i am hoping this guy refrains from future crt air cleaning.
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Old 02-16-2006, 01:12 AM   #6
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Default Re: Messing around inside CRT monitors - danger considerations

[QUOTE=Topcat]If you must remove the anode wire, discharge the CRT first!! ]/QUOTE]And just before you replace the anode wire, discharge the CRT again because I learned the hard way that the CRT regains its voltage after being discharged.

Also don't let the monitor tip forward, which it's apt to do because most of the weight is at the front. I read of someone who placed his 19" monitor on his bed, and it crashed to the floor and its CRT shattered.

I found a couple of 17" Envision monitors yesterday, an EN-710e and EN-775e, waiting to be hauled away by the trash collectors. They seem to work fine and are cosmetically perfect. Envision used to send out repair manuals by e-mail for free, and I hope they'll do this for the EN-775e.
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Old 02-16-2006, 04:40 AM   #7
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Default Re: Messing around inside CRT monitors - danger considerations

Is the flyback the board on the back of the crt, and if so, should it be loose? My monitor that I wack to get the picture to come on seems ok inside everywhere but that board.
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Old 02-16-2006, 06:47 AM   #8
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Default Re: Messing around inside CRT monitors - danger considerations

Quote:
Originally Posted by willawake
wish i could have learnt crt repair, got one sony g200 dead, one 15" sony trinitron fading picture and now black only, and one sony 17" trinitron which has problems starting each day (my main office screen) needs several pushes of the button and removals of the power cord to get going, dont know if i should leave it on all the time maybe.
I think Sony makes our jobs as techs harder on purpose - I've worked on a few of them, and it's been not much fun every time. Additionally, most RGB adjustments among others are done using Sony's special software and interface, including my Dell P991.

I had a Sony/Dell 15" I bought for $25 that was really dim... opened the back to try and tweak it a little. Ended up giving it away to my sister two hours later because there was nothing to tweak in it.

My P991 glitches out from time to time - it will briefly flash and lose geometry for a split second, or on rare occasions power itself off and back on. Soon as it dies for good it gets replaced by something not made by Sony
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Old 02-16-2006, 03:04 PM   #9
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Default Re: Messing around inside CRT monitors - danger considerations

Quote:
Originally Posted by Spacedye69
Is the flyback the board on the back of the crt, and if so, should it be loose? My monitor that I wack to get the picture to come on seems ok inside everywhere but that board.
The flyback transformer is a chunk of plastic about 2"-3" square that's soldered to the big circuit board and has a thick cable with a suction cup on the end that plugs into the side of the CRT. It looks sort of like this: http://www.mcminone.com/content/prod...s4/4065139.jpg but is usually all black.

The thing that plugs into the back of the CRT is the video amplifier/driver board, and it will wiggle a bit but shouldn't be loose. In fact many manufacturers glue it to the glass with silicone sealer. Sometimes the sockets that plug into the CRT pins work loose, but can usually be pinched or pried tighter with pliers or a jeweler's screwdriver.

A great website for electronics repair info: http://www.repairfaq.org
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Old 02-17-2006, 06:10 PM   #10
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Default Re: Messing around inside CRT monitors - danger considerations

As with being shocked by a CRT monitor, I have experienced being shocked by those prankster shocking things and it's no fun to be shocked.

I would avoid opening up the cover of a CRT monitor.
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