[rescue] Rescued iMacs looking for input on repair

Patrick Finnegan pat at computer-refuge.org
Wed May 5 15:56:20 CDT 2004

On Wednesday 05 May 2004 15:23, William Enestvedt wrote:
> Bill Bradford wrote:
> > On the other hand, we had a tech support guy / stoner who would
> > discharge CRTs with nothing more than a large, long flat-head
> > screwdrive and an impressive "BANG!".
>    I have a question after reading this: you kept a stoner _on
> staff_? Wait, no, I have a different question: how can you discharge

How else do you ensure a supply of ... never mind. :)

> one of these man-almost-killing capacitors without getting zapped?
> Does the metal implement have to be grounded to something (besides
> your central nrevous system)?

Yeah, you either use a couple Meg-ohm resistor to the grounded chassis 
(make sure the chassis is grounded!) or just just an allegator clip 
lead to the chassis.  It's safer to use the resistor, so you avoid the 
"BANG!" and avoid killing semiconductors in the device.

>     Not that I'll ever do it, since I know that I *don't* know which
> parts are the scary ones inside that metal shield that lines a CRT
> case. -wde

Well, a good rule of thumb (for a powered-off monitor) is the HV cable 
to the monitor, and what's under the anode cap (the connection on the 
relatively-thick HV wire) is dangerous.  For the most part, the rest of 
the ciruit has sub-kV voltages when turned off.  Of course, power 
supply capacitors can still be unfriendly to touch.

Purdue University ITAP/RCS        ---  http://www.itap.purdue.edu/rcs/
The Computer Refuge               ---  http://computer-refuge.org

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