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Discharging

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Nipedley:

Okay okay.. I've read like 20 guides on this and they all seem to say something different "use a grounding rod" "take the monitor out of the cab" "unplug everything"..
but, if it was all unplugged where would the charge go if it had nowhere? through the board? wouldnt that fry it? It's my understanding that it needs to be grounded but these guides tell different stories

I have a few questions;
does my monitor need to be inside the cab?
does it need to be connected to anything (if so what)?
if not, then where the hell does the charge go? into the air?

thank you

MonitorGuru:

Read the "Do I need to discharge my monitor IF..."

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.

Q*Bert_OP:

Wich wa do I put the resistor when discharging, or does polarity matter?

MonitorGuru:

Resistors are non polar. It's just (most) electrolytic capacitors and diode based things (e.g. diodes, transistors) that are polar.

In other words doesn't matter. Easiest is to place it between the frame and the grounding clip, but some put it between the screwdriver and clip.

You can't just use a plain old baby resistor either, you'll fry it AND not disappate the charge (that's why it's best to have no resistor as you can hear the zaps, but some state it could cause damage to the circuitry/tube, but I've never found that to be the case.

A proper resistor value is HIGH wattage (not a low 1/4 watt one) and somewhere in the range of 1 to 10 Million ohms.

Here is more info about discharging tubes: http://www.eio.com/repairfaq/REPAIR/F_captest.html#CAPTEST_008

REMEMBER Discharging the tube DOES NOT discharge any capacitors on the chassis. Most of them are harmless, but the super large filter one next to the fuses and/or flyback CAN HURT ALMOST AS MUCH AS THE TUBE.

Therefore if you plan on working on the chassis board, be sure this capacitor is discharged as well.. Normally, if the monitor is working, there should be no charge in it. But if the chassis has a blown fuse and you plugged it in to try it and got nothing, there is likely a huge voltage waiting in the capacitor as the blown fuse won't allow it to disappate correctly.

Discharging it is virtually the same as the tube. Just find both terminals (+ and -) and short them and expect a big pop and flash if it has a charge. Wait and do it again.

A lot of people say it's safer to discharge these with a resistor as it's hard on the electrolytic if you don't. Use a large resistor again and let it slowly discharge and test it with a 200 volt meter to see if there is any residual charge left before touching things on the board.

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