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Mickey Juice
14th November 2005, 11:10 AM
Just checking that this is the correct technique before I go ahead and discharge my monitor <insert warnings etc here>

Use an alligator clip lead, one end connected to an insulated screwdriver and the other clip onto the wire braid that goes around the monitor.
Insert the screwdriver under the anode cap. Take it off and repeat.
Also ground any large caps on the chassis board.

This method won't kill the gameboard or any other circuitry will it? :(

I'm asking as i've been reading differing methods on the net, and it's getting confusing. This is the way I was shown when I did some work experience at a TV repair place a few years ago. Other methods I read were discharging into the mains wall socket earth pin (:redface ) and the other was discharging into the steel bracket holding the monitor.

Berty
14th November 2005, 11:22 AM
I would disconnect the gameboard as a matter of precaution. I have only seen the method where you ground to the monitor frame :unsure

Mickey Juice
14th November 2005, 11:26 AM
I think the wirebraid is connected to the monitor frame anyway.

hamish_nz
14th November 2005, 11:54 AM
Get an extension cord and cut the female end off leaving the prong end.
Then strip about 400mm of the outer casing from the cut end. Then cut the +&- wires off leaving only the ground wire. Attach this to a screw driver.

Hey presto a discharge tool.

plug it into the wall (POWER OFF), slip the screw driver tip under the suction
cup and the charge is safely discharged with the houses earth.

Berty
14th November 2005, 12:28 PM
...so long as your houses earth is all hooked up correctly (just thinking about a mythbusters episode i saw)

Mickey Juice
14th November 2005, 12:51 PM
Thanks Hamish. Does that method work fine for you?

@ Berty. Was that the lightning in the shower one?

More food for thought:

I've seen your pages about handling video monitors.
However you're very secure and precise with this there is one thing you forgot to mention.
You should NOT ground the anode of the tube DIRECTLY to ground.
ALWAYS use a resistor of 1 Mega ohm between earth and anode.
Direct grounding can cause the cascade rectifier to die.
Using 1 meg won't affect the discharge at all and will completely discharge the remaining high tension.

The problem in this is that when grounding the tube you also ground the cascade. The very high charge, especially when just turned off, is present on the anode but ALSO on ALL stages of the cascade. As you probably know the cascade is a chain of high tension diodes built in a solid state housing. The discharge can cause the underlaying diodes in the cascade to discharge THEIR charge through the "upper" diodes, thus blowing them. IE, the charge can eventually blow from line transformer THROUGH the entire cascade. Sometimes these units are built together in a single housing, making the exchange even more expensive.

Just one tiny little resistor, costing almost zilch, can prevent this.
Check this out, some TV's have a build in discharge unit almost exactly the same construction as you described, only with a built in resistor.
Other manufacturers put a warning on the picture tube to discharge only with a resistor.
Now why would they do that ?

I'm also aware of the fact that this resistor is not always used by "qualified" service personnel.........
So far the statement qualified.

The cascade won't always blow, but it sure can and sooner or later you will find that you just did ran out of luck (and a lot of money

Berty
14th November 2005, 12:57 PM
yup, such a great show!

hamish_nz
14th November 2005, 01:20 PM
Ive used the house ground method on monitors over 40 times without any
problem. I have used this on monitor that have been on minutes
before hand.

After you take the suction cap off also touch the outlet hole on the
tube itself sometimes there can still be some charge.

You can stick the handle of the screw driver in a platic tube
like a vacume cleaner tube. that way you can be further way.

Arcade King
14th November 2005, 01:22 PM
I've been doing a lot of this of late and the correct way is to get a nice thick peice of wire you can wrap one end to a bolt or any part of the monitor metal chassis or what I did was solder a pair af aligator clips to each end.

Put the other end of the wire to your screw driver put your hand in your pocket ;) then slide the screw driver under the suction cap until you touch the anode. You may here a snap noise but out of the 10 or so times ive done it its only happend once. I flick the anode clip out and come back a few more times sticking the screw driver in the hole discharging any left overs.

I'd be weary of sticking one into the power socket just in case your hous eisnt earthed right.

I usually use my multi meter to check the end of the screw driver and the metal chassis of the monitor to make 100% they are connected.

Mickey Juice
14th November 2005, 01:34 PM
Here is some more info. I think i'll discharge into the monitor's metal earth braid, rather than directly to the houses earth.

What about discharging the capacitors on the PCB/chassis? Do you just discharge them by touching with the earthed screwdriver??

***

The tube is a capacitor (or, think of it as a battery). The inside of the tube is connected to the large red anode wire under the grey cap

The outside of the tube is connected to a metal grounding strap that runs to the neckboard and also contacts the metal frame.

Therefore you short the ANODE to the CATHODE, or in otherwords the two parts of the tube. This has NOTHING to do with earth ground or any other "point of contact". Just like to short out your car battery, connecting either terminal to an ountlet in your house won't do anything, you have to short them across each other.

Some people just short it with a wire clipped to a screwdriver and the metal frame. Others "bleed" the charge with a resistor in line.

****


When discharging to the chassis frame, you're "shorting" the capacitance built up within the tube.

Basically, you're shorting the + anode inside to the - cathode outside.

You're NOT shorting it to "ground" or "neutral" with respect to the mains (AC) outlet..

In fact, since all arcade monitors are isolated from ground & neutral through the use of an isolation transformer, even if you DO have it plugged in, you still don't have a "straight line" to ground/neutral.

[And think about it... even if you could short it to ground/neutral... do you want a 22 Kilovolt zap travelling through you're home's neutral line on the AC until it hits ground outside your house on the transformer?Huh? Probably not!!!! Smiley ]

Basically, just think of the picture tube as a big massive electrolytic capacitor.

One lead is + (the anode cap, that leads to the capacitance charge plate on the inside of the tube), and the other is - (the outter glass plate on the tube that *should* have a ground wire wrapped around it!).

When you short it, you remove the capacitance built up between the plates, just like shorting 2 wires of an electrolytic capacitor. You don't dissappate an EC by connecting the + lead to your AC wiring ground or neutral... you just disappate it to the - on the capacitor itself.

If you search google you will find some people claiming that if you dont slowly discharge (through a resistor of some type), you will ruin the tube. Others claim that's hogwash and leaves you more susceptable to a lingering charge that never disappated, and can still hurt you.

The choice is yours... believe who you want. I always have just grouned it out to the frame (that is electrically connected to the outside of the tube--always checked with an Ohmmeter before I do it), but never had a zap, as the discharge circuitry was already working and no charge was still in the tubes, but you need to always be careful and never assume. I trust what Bob says so I go with the quick zap route.

Arcade King
14th November 2005, 01:35 PM
echo echo

Mickey Juice
14th November 2005, 02:07 PM
echo echo

I just thought the other info regarding the discharging to ground outlet was interesting and relevant.

Arcade King
14th November 2005, 02:22 PM
it was :) just being a smert arse is all:117:

hamish_nz
14th November 2005, 02:46 PM
That makes sence. Time to teach an old dog a new trick.

Mickey Juice
14th November 2005, 03:04 PM
Here's a decent guide. Too bad they dont mention discharging caps on the chassis... :?

http://www.arcadegames.net/sightsound/discharge.ppt