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Comment by 29athrowaway | Hacker News Reader

Have lots care when opening a CRT TV. In fact, don't do it unless you know what you are doing.

I remember fixing up a CRT on an arcade machine I had in my office at work at one point. I read up on how to discharge it and made a makeshift tool to do the job (i.e. an insulated screwdriver with a wire attached to ground). I was pretty scared and even made sure to do it during work hours when others would be around in case I got zapped unconscious. :) Once I got was able to do it a couple of times, it really was no big deal, but I did take care not to get too close to the back of it while the thing was on and exposed.

Worse, it’s never been made clear to me which parts are the dangerous one. Just a lot of vague hand waving. Which I guess is fine if you don’t want liability?

If you're not sure about it, best to stay away. With a cursory web search or YouTube search, you can find plenty of information.

That’s probably because most people posting this useful advice don’t know themselves.

If unsure or nervous around electricity, just ground the segment you are working on first.

But the parts that should make you extra cautious have wires with a lot of insulation so they look thick. those are the 20Kv bits. you also will want to take the time to drain any big capacitors. you can just short the leads or if you are feeling conscientious(and don't like sparks) drain them with a resister(100kohms or so) between the leads.

The cathode ray tube is a giant capacitor. During operation it is charged to 20+ kilovolts, and it takes a long time to discharge even after being unplugged from the wall. (Some but by no means all TVs have a circuit which discharges the tube). There are also large capacitors in the power supply which maintain hundreds of volts even after being unplugged. When the TV is connected to power, the flyback transformer (a large circular device soldered to the main board) generates a range of voltages from hundreds up to 20+ kV which are wired to various parts of the tube. Some of these are present on the neck board which is exposed at the pointy end of the tube.

US TVs are extra spicy because they sometimes have no earth, so if the power is wired backwards (either in the plug or more insidiously from the wall), everything metal inside the set can be live.

If you overvolt the tube (a worry with this replacement board actually) then it can emit x-rays. Most "modern" CRT main boards have a circuit which detects this, but maybe older ones or cheap knock-offs don't.

In short, if you don't know what you're doing, stay away.

Ok. I can identify all of those parts and once did a cap replacement on a pac-man monitor. But that's enough to keep me from making it a regular thing.

A few sets I've had need to be on and open to make adjustments. I'm never a fan of that.

This is a case where having the right tool is actually a good idea. It'll have plenty of insulation and usually a VU meter showing the voltage (so you can see if it was charged and watch it drain). A screwdriver doesn't really have enough separation between you and the 20+ kV :-/

In what cases of repair is having the right tools not a good idea?

Its not a matter of not having the right tool is not a good idea, but sometimes, because of cost and or circumstances, you have to improvise and/or make due with what you have.

When I took a TV servicing class in high school in the 1970s we were told just to keep our left hands in our back pockets so the discharge will ground through our right side and not across our hearts. The biggest hazard was breaking our hand on the chassis as we jerked back from the shock.

I never heard of any kids getting hurt, so it was fine.

The risk of death or serious injury messing with CRT displays is grossly overstated (note the lack of data on related fatalities). Use common sense and you'll be fine.

If you wear rubber gloves and keep your other hand in the your pocket, I dont see any actual problems.

Also long sleeves are good, I was recently zapped at the wrist when fixing an oscilloscope.

I think maybe the 20 kV abates rather quickly on its own, because I dont remember using much any caution when unplugging the anode plug.

Has to be serious rubber gloves to withstand 20kV :) the simple doctor's ones won't do

Surgical latex gloves are not what I picture when someone says "rubber gloves" but something more substantial typically used when cleaning in a shape that borders on a rubber gauntlet.

I know but not everyone who reads this would be as experienced to know this :)

Some people would still think "it's rubber so it doesn't conduct electricity so I'm fine messing with this TV".

But yeah CRTs are now so rare that I agree that it's very very unlikely for someone without much knowledge to tinker with them. You have to be really an enthusiast to even still own one let alone try to repair one instead of picking up a nice cheap flatpanel.

Personally I'd forgo the gloves (real protective ones are so clumsy it's hard to really do something productive with them) and make sure the caps are fully discharged. Though generally I'd steer clear from this stuff as I know I don't understand it well enough. I came up in electronics during the final years of CRTs so as my knowledge grew they became deprecated and I never really got the full grasp of them.

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