Monitor discharge?

Hi guys,

so i'm attempting to do a cap kit. Here's the problem, haha... So i went to discharge this beast, got a screwdriver, lamp cord, hooked one end to a spade and screwed it down to the monitor chassis, and hooked the other end to the screwdriver. I slipped the driver under the suction cup thingy, and felt it hit the pins, etc.. but no noise? no spark? nothing? so I'm moving it around, and eventually i ended up knocking the whole clip thing off. So now I'm afraid to go any futher, because although the clip is off, I don't know if I actually discharged the monitor? It's an electrohome GO7 and it's only been unplugged for a day.

should I proceed?

edit: oh, and the unit is unplugged from the wall of course, and I've made sure my makeshift probe is actually electrically connected to the chassis (0 resistance).

You won't always get a spark/crackle/pop. I have one monitor that will only make a noise if I just recently turned it off. Others that have been off for one day won't make a noise at all. You've checked your circuit, so that eliminates that. Now that the suction cup is off, you can always do the same thing again, touch your screwdriver to the end of the clips on the cup. You can also look at the bigger caps on the monitor chassis and short those by hand with the screwdriver. Just touch the two terminals together with the screwdriver.

As a side note, this whole "you will die if you don't discharge your monitor while standing on a 3' wooden stool, wearing a full rubber suit and huge screwdriver" is really overblown. Sure, you can get a very nasty shock from a monitor, but most likely will not kill you. I know several people who've been shocked from a monitor/TV and lived to tell about it.

You'll be fine.

As a side note, this whole "you will die if you don't discharge your monitor while standing on a 3' wooden stool, wearing a full rubber suit and huge screwdriver" is really overblown. Sure, you can get a very nasty shock from a monitor, but most likely will not kill you. I know several people who've been shocked from a monitor/TV and lived to tell about it.

Click to expand...

soooo true. I shocked myself on the anode cap before discharging an old tube- a nanao 26. These wont discharge themselves quickly like most chassis either, so it hurt like hell. but I lived.

FYI, almost all chassis run on under 200v (usually around 135v). so even if the caps aren't discharged you really can't die. People just blow that up so out of proportion. TVs are dangerous but they're not that dangerous.

Thanks guys,

I attempted grounding the pins like a million times and nothing happened, so I thought it must be safe. I did the cap kit no prob! Looks great now.

madman said:

Now that the suction cup is off, you can always do the same thing again, touch your screwdriver to the end of the clips on the cup.

Click to expand...

EEK! Holy freakin' shock-me Batman! The suction cup is NOT the source of the shock. The CRT acts as a big capacitor and stores the charge on the inside surface of the tube. You want to touch the screwdriver again to the little hole in the side where the cup clips in.

Touching it to the clips after its disconnected will do nothing.

Also, you really want to discharge the tube, wait five minutes and discharge it again to really make sure you discharged it. The tube is still holding a charge even if it doesn't crackle. The crackle only happens if the tube is fully charged. It can still hold a partial charge and not crackle.

Still, it's not a HUGE deal. Ever been shocked by a lawnmower spark plug? It's like that.

madman said:

You can also look at the bigger caps on the monitor chassis and short those by hand with the screwdriver. Just touch the two terminals together with the screwdriver.

Click to expand...

AAAAH! I guess you've never melted a screwdriver tip before. You should use a high power resistor to do that. 10K should work fine and discharge it slow enough to avoid arcing or melting things and to keep the cap from being damaged by using a screwdriver.

segasonicfan said:

FYI, almost all chassis run on under 200v (usually around 135v). so even if the caps aren't discharged you really can't die. People just blow that up so out of proportion. TVs are dangerous but they're not that dangerous.

Click to expand...

Yes, they run on 110-120v in the USA, however that goes through a full wave bridge rectifier so you do end up with more than that in DC voltage. If the current crosses your heart, yes you can die. Those caps store enough energy to melt chunks out of a screwdriver.

Now, let's face it... the reality is that the odds of death occurring are absolutely miniscule.

However, I had 3 scars on my hands that took years to finally fade away from a switching power supply board I picked up which had charged caps on it. It's DC voltage which makes your hands clamp down on it HARD so you might not be able to let go of it. That was friggin' painful!

So... play it safe.

Most units have enough current draw to drain the power supply caps quickly - on the order of a few seconds at most. The ones you have to watch out for are ones with switching type power supplies which are mainly the newer ones. Those should have bleeder resistors built-in that are on the order of 100k to 150k ohm in size to help discharge them. The power supply I was working on didn't have those bleeder resistors and could hold the capacitor charge for days.

Now that I've scared everyone... that old G-07 monitor's power supply section won't hold a capacitor charge for more than a few seconds. Double-check it with a voltmeter but you'll be fine. Wait 5 minutes after discharging the CRT and hit it again with the grounded screwdriver to make sure any residual charge is bled off.

Take your basic safety precautions and you'll be just fine.

RJ

Keeping in mind, to cross your heart would mean you'd have to use both hands discharging the monitor and put both of them to the back of the tube/anode cap (both hold charges from what I've seen, but the tube moreso). So yeah risk of death is miniscule.

the voltages I was referencing are DC too, so they are nasty as well, not simply AC input I was talking about but the actual voltages powering the chassis after the AC is converted to DC and then run through the regulator.

So yeah, ppl should be careful and you can get a nasty shock, but I get really tired of everyone going on and on about how you can die messing with a TV. Most people that I've spoken with think the chassis is what can kill you too and I've even come across detailed and ludicrous stories about caps on the chassis holding charges for a year and then killing people. I've worked quite a bit with CRTs now and have done many mods and repairs on chassis and it's just very hard for me to believe the stories.

That said, when I do work on fixing people's TVs they think I'm putting me life on the line so I can pretend to be superman

channelmaniac said:

EEK! Holy freakin' shock-me Batman! The suction cup is NOT the source of the shock. The CRT acts as a big capacitor and stores the charge on the inside surface of the tube. You want to touch the screwdriver again to the little hole in the side where the cup clips in.

Touching it to the clips after its disconnected will do nothing.

Click to expand...

My thought was that would discharge the caps on the chassis.

I haven't ever melted a screwdriver by shorting out a cap, but have never done that on a monitor chassis. I've gotten some nasty shocks in my day from unexpected places so I'll usually short any big caps before tinkering around.

Someone really should make a proper monitor discharging FAQ/website, as all the ones out there will have you preparing your will and purchasing your gravestone.

madman said:

Someone really should make a proper monitor discharging FAQ/website, as all the ones out there will have you preparing your will and purchasing your gravestone.

Click to expand...

They do that for safety and financial reasons. If someone reads it, does it, and gets hurt the lawyers will sue everyone included and let the courts settle it - common sense be damned.

Most people aren't smart enough to put one hand in their pocket when discharging things. They hold onto something with the free hand to steady themselves. When it is metal then there exists a path for the current to go across the heart when they mess up.

Those are also the same people that aren't smart enough to remove rings and watches when messing with monitors, power supplies, or even when doing home electrical work.

Just look at an electrician's hands. They don't wear watches or rings when working. Then look closer at them. Some will have nasty scars on their ring fingers to remind them to remove their rings. DOH!

Thanks for all that info channelmaniac

I had a feeling the charge was in the CRT itself, so yes I did ensure my screwdriver was touching the inside of that hole as well as the pins on the anode. In fact I did pretty much everything I could to do make sure nothing could have a charge.

Ok as for discharging chassis caps for the future, how should I use the 10k resistor? Should I just put the resistor between two probes/screwdrivers and touch each side of the bigger caps? and if there IS a charge, would a multimeter show it?

Last question, now that everything is lookin fine, I've noticed that the picture is slightly slanted, and I can't find a good answer on how to fix that. A few answers from old rec.games.video.arcade posts said to adjust the yoke.. what part is the yoke? how to adjust? do I have to discharge first?

You can use a multimeter to measure the voltage across the caps. If it's zero or almost zero I personally wouldn't bother with the discharge resistor. You can hold one of the leads with a pair of pliers and make sure the leads touch both solder joints.

I would avoid holding it by hand as the resistor could get pretty hot depending on the current being passed through it.

As far as the tilted picture goes, that is a yoke adjustment. The yoke is the big coil of wire on the neck of the picture tube. There is a bolt of some kind that you loosen and then you can turn it. It doesn't take much of a turn!

Also, be aware that if the color is perfect on the monitor you may be off a bit after you move it. By off I mean that white areas will have a bit of blue or red shading around the edges. This is caused by the color guns not being fully aligned. That is not a job for a n00b (newbie)

Raymond

Hmm yes I believe I would still consider myself a CRT n00b. The color problems are the convergence problems right? If my convergence thingys are hotglued in place, would I still get problems after adjusting the yoke?

Possibly. The rings are magnetic and help to direct the electron beams to hit specific places on the crt face. When you rotate the yoke those beams will be slightly different in their alignment to the crt face.

RJ

Webmiester, does your monitor's chassis allow for screen adjustments of that nature? My Egret II had two separate panels, one for common adjustments like contrast and H/V size and pos, but a separate panel for geometry related adjustments. I was able to fix a trapezoid pattern problem with the adjustments.

CM, I used to work with a guy who was in the Army I believe it was. A guy he was working with in the field was working on some high voltage cage with his wedding ring on. Guy gets a huge shock to his hand, recovers from the shock and thinks nothing of it. Turns out the shock had severed his finger at the wedding band and cauterized it. Not sure if the story is true, but I don't see why someone would make that up.

madman, i don't think so, it's just an electrohome GO7.

channelmaniac, I wonder about the convergence problem because I doubt it was calibrated when the problem was present. It converges fine now, but the yoke is off.. I assume the convergence was fine before the yoke moved?

Or is this more of an electrical thing.. like I think logically I _should_ be able to move the yoke without disturbing the convergence _because_ that's the original set up of the monitor, when it was hotglued.

any thoughts before I attempt it?

I've heard similar stories of rings getting so hot that it cooked the flesh... that means amputation time, but I've never personally seen that. I've seen the burned ring fingers though.

The G07 is ancient. It doesn't have geometry correction knobs on it.

Take a bit of whiteout and make a line on the neck of the tube and end of the yoke. That way you know where to put it back if you need to.

RJ

channelmaniac said:

The G07 is ancient.

Click to expand...

It came off the arc

channelmaniac said:

Still, it's not a HUGE deal. Ever been shocked by a lawnmower spark plug? It's like that.

Click to expand...

Haha that's how my old man checks the distributor on his car.... Stick a screwdriver up there and crank it.... If it shocks the hell out of him the plugs are getting juice.