Re: Bleeder Resistors and the Zen of Monitor Discharge

Excellant description, do you mind if I add it to my monitor removal
instruction page?

John :-#)#

At 11:57 AM 4/23/2000 , John Mehrtens wrote:
> Hi everyone! Here are some notes relating to this thread (on the
>Vectorlist):
>
> If you can, check out some of your local electronic surplus
> stores. I've
>always used a 'Monitor HV Discharge Tool', and thought everyone else was in
>the same practice. It's a requirement for working on old monitors without
>integral bleeders. I've picked them up in the past for a song at the
>surplus stores - usually only a couple bucks each - and have given them to
>others who work on monitors.
>
> There are a couple things to remember -- if you're using a
> discharge tool,
>take a little extra time holding it under the anode cap. It "slowly"
>discharges, taking several seconds to discharge the tube fully. At least
>with this, internal components will be spared.
>
> An instantaneous discharge of potential, although the CRT is fed mere
>milliamps of current, by definition is a discharge nearing infinite
>amperage. I know it sounds odd, but by definition an instantaneous change
>from one potential to another (taking "NO" time) involves the release of
>infinite amperage. Now, since this is impossible (everything takes time -
>the speed of light is finite), a 'virtually instantaneous' release therefore
>approaches this amount. By using a bleeder resistor, you extend the
>discharge over several seconds, minimizing the amperage released. It also
>keeps the flyback from causing a huge backlash of current as the field
>within the transformer collapses.
>
> If you use resistors in a home-made bleeder, make sure of two
> things. One
>is that you're very well insulated from the potential, and the other is that
>the resistors are capable of holding this resistance at the high potentials
>involved without arcing. You don't need to worry about the power handling
>capability (no need for a 5-watter at 4, 6, or whatever-megohm where a
>1-watt resistor will work fine) since you're not trying to carry a load upon
>the potential and amperage involved - you're just discharging it. Just be
>sure it won't arc from one lead to another while you're discharging the CRT
>or your efforts will be for naught.
>
> 24-gauge silicone insulated HV cable will work
> beautifully. Don't use Zip
>cord - that's overkill in the gauge, and underkill in insulating qualities
>(600V is a heck of a lot lower than 25kv). Always discharge to the chassis!
>A while ago I saw a site where some fool used heavy cables attached to the
>grounding pole on a home outlet, while shoving a screwdriver under the cap.
>I think there was even a thread about this site on the lists. Needless to
>say, that was a site showing exactly how NOT to discharge a CRT.
>
> If you hear a loud 'snap' when you discharge, that's
> bad. <grin> Reverse
>current is your enemy. It should be inaudible or a very slight 'click' when
>you discharge the anode.
>
> Hope this helps!
>
> John
>
>---------------------------------------------------------------------------
>** To UNSUBSCRIBE from vectorlist, send a message with "UNSUBSCRIBE" in the
>** message body to vectorlist-request@synthcom.com. Please direct other
>** questions, comments, or problems to neil@synthcom.com.

  John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
  Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
  http://www.flippers.com
         "Old pinballers never die, they just flip out."

---------------------------------------------------------------------------
** To UNSUBSCRIBE from vectorlist, send a message with "UNSUBSCRIBE" in the
** message body to vectorlist-request@synthcom.com. Please direct other
** questions, comments, or problems to neil@synthcom.com.
Received on Sun Apr 23 21:19:12 2000