3 Jun
1998
3 Jun
'98
1:39 p.m.
<I have wanted to ask this for a while. What is the actual risk of me
<blowing myself up if I service a machine with a built-in monitor?
<An example is the Mac SE. Is there any risk involved (as long as I
<don't short capacitors with my fingers) in taking it apart? What are
if your careful and aquaint yourself with where the HV is...and make
very sure you don't put your fingers there you should be ok. Also
remember that 17,000 volts can jump a good distance and find you
fingers.
To make a point though... I got blasted fixing a VR201 monochrome monitor
yesterday. So you know this monitor is powered off 12v in the pro350.
Well, I kept clear of the flyback and crt anode and got nailed by 70-100v
down on the logic board. I wasn't watching for the focus cap having
anything big voltage wise on it. Many monitors have points other than
the CRT where higher than supply voltaged can be found and some can really
sting!
<the parts I should watch out for? How long do they hold a charge?
<Could I discharge them?
How long... amazingly long and should be treated as charged until proven
otherwise. You can discharge them, make sure the "ground" you use is
a real one and simply not the case or some other floating point.
Allison
3 Jun
3 Jun
2:58 p.m.
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4:17 p.m.
At 12:58 AM 04-06-98 +0100, Tony Duell wrote:
Not _that_ far - less than an inch, I'd have
thought. And remember that
the EHT side is pretty well insulated, so you're not going to touch it by
accident.
I seem to recall that the ionization potential of air at STP is something
like 10KV/cm, so 17KV might nearly jump an inch on a good day with a tail
wind.
If you really need to know I'll give my Dad a ring - he's a retired
ionization physicist who used to play with real big Van der Graf generators
(by really big I'm talking 10m tall and 5MeV - used to generate real big
sparks!).
I've never zapped myself with HT, but have successfully survived connecting
myself to 240V 50Hz - don't try this at home folks (or anywhere else) - it
hurts....
Huw Davies | e-mail: Huw.Davies(a)latrobe.edu.au
Information Technology Services | Phone: +61 3 9479 1550 Fax: +61 3 9479
1999
La Trobe University | "If God had wanted soccer played in the
Melbourne Australia 3083 | air, the sky would be painted green"
5:05 p.m.
Huw Davies wrote:
At 12:58 AM 04-06-98 +0100, Tony Duell wrote:
Well, I _did_ once discharge a Leyden jar that had been charging for
an hour sort of by hand. (Well, I first hit it with the physics lab
grounding strap, it made a _really_ big spark that I thought did the
job. Seems that took care of all of the electrons that could manage a
jump of a full inch. So I grabbed it to put it into the cupboard.)
Picking myself up off the floor a couple of minutes later ... I put it
away, it was now _thoroughly_ discharged.
--
Ward Griffiths
They say that politics makes strange bedfellows.
Of course, the main reason they cuddle up is to screw somebody else.
Michael Flynn, _Rogue Star_
Not _that_ far - less than an inch, I'd have
thought. And remember that
the EHT side is pretty well insulated, so you're not going to touch it by
accident.
I seem to recall that the ionization potential of air at STP is something
like 10KV/cm, so 17KV might nearly jump an inch on a good day with a tail
wind.
If you really need to know I'll give my Dad a ring - he's a retired
ionization physicist who used to play with real big Van der Graf generators
(by really big I'm talking 10m tall and 5MeV - used to generate real big
sparks!).
I've never zapped myself with HT, but have successfully survived connecting
myself to 240V 50Hz - don't try this at home folks (or anywhere else) - it
hurts....
Huw Davies | e-mail: Huw.Davies(a)latrobe.edu.au
Information Technology Services | Phone: +61 3 9479 1550 Fax: +61 3 9479
1999
La Trobe University | "If God had wanted soccer played in the
Melbourne Australia 3083 | air, the sky would be painted green" 
4 Jun
4 Jun
4:11 a.m.
Guys,
Reason I was bit vague and explaining things bit strangely like this
but! I love to see you drve in there BUT you have asolutely no idea
what they are. All you need is one touch, you get bit or body bag.
Reason I warned you that, and triple reason is that you need to get
your friendly guy local in your area to point out in like when TV is
open so guy can show you where to watch out and explain many
components to you so you will understand more fully what they are
for.
That way, you will live to old age. Seriously. :)
By the way, I did some dumb things in my younger days, I got zapped
by a bad plug by a one hand. Pulses of zaps. Zapzapzapzap!!!
Ditto to when I touched something inside old monitor that is not
meant to be touched. Blew up a green neon lamp by mistake,
impressive bang.
Also one hand behind or in pocket rule is VERY GOOD for one reason.
Keeps you safe and prevent you from making full circuit and flash
into heap of ashes. Bad Thing to stand in wet or damp spot too.
When I was on a job experience (full time), someone had me to
discharge the tube with a wire clip grounded to tube wire straps and
a long insulated flat screwdriver. Even on a 12" tube, still makes
good LOUD SNAP! with bright flash of blue lightening. These guys who
taught me that is totally WRONG after a research in proper
discharging tubes. Build your own discharging tool, using high
quality stuff, using 2 or 3 50 or 100W 10K ohms cermeric resistors in
series encased in silicone glue inside a length of insulating tube to
prevent arc over. And leave it there for 2 mins just in case.
Leave out those microwaves. Simply too dangerous than monitors and
switching PSU's. Primary danger is that hunk of capacitor still
charged up with high current and at about 5Kv and you have to go very
careful to make sure all the seals is good on microwave. It's
actually cheaper to just replace that with new microwave than try to
fix it. BTW, the connections inside those microwaves is often
exposed.
Jason D.
email: jpero(a)cgo.wave.ca
Pero, Jason D.
11:33 a.m.
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5:32 a.m.
At 06:39 PM 6/3/98 -0400, you wrote:
<I have wanted to ask this for a while. What is the actual risk of me
<blowing myself up if I service a machine with a built-in monitor?
<An example is the Mac SE. Is there any risk involved (as long as I
<don't short capacitors with my fingers) in taking it apart? What are
if your careful and aquaint yourself with where the HV is...and make
very sure you don't put your fingers there you should be ok. Also
remember that 17,000 volts can jump a good distance and find you
fingers.
To make a point though... I got blasted fixing a VR201 monochrome monitor
yesterday. So you know this monitor is powered off 12v in the pro350.
Well, I kept clear of the flyback and crt anode and got nailed by 70-100v
down on the logic board. I wasn't watching for the focus cap having
anything big voltage wise on it. Many monitors have points other than
the CRT where higher than supply voltaged can be found and some can really
sting!
<the parts I should watch out for? How long do they hold a charge?
<Could I discharge them?
How long... amazingly long and should be treated as charged until proven
otherwise. You can discharge them, make sure the "ground" you use is
a real one and simply not the case or some other floating point.
Allison
This is sort of off topic, but also sort of funny so please forgive me.
Many years back, when I was doing tv repairs, I had a St Bernard. One humid
summer afternoon while trying to repair a set I poked my insulated
screwdriver into the high voltage supply. Nothing happened except the hair
on my arm stood up. I pulled out the screwdriver and the hair went back
down. I poked the screwdriver back in and the hair went back up. About then
the St Bernard came up to be sociable and a spark jumped about three
quarters of an inch from my arm and hit him in the nose. He was not amused
and would not come near me until his appetite got the better of his
feelings at supper time.
Regards
Charlie Fox
9546
days inactive
9547
days old
7 comments
6 participants
participants (6)
-
allisonp＠world.std.com -
ard＠p850ug1.demon.co.uk -
foxvideo＠wincom.net -
gram＠cnct.com -
H.Davies＠latrobe.edu.au -
jpero＠mail.cgo.wave.ca