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Old 08-16-2010, 08:11 AM   #11 (permalink)
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Default Re: Computer Turns on but no screen?

I have never once seen a cap on a motherboard blow someone across the room :-p

The ones on the motherboard are very small, and weak compared to the ones you seem to be thinking of.

Anyways, removing the battery from the motherboard, and pressing the power button is standard procedure, I think it is even asked on the A+ exams on how to properly discharge the caps and they say use the power switch, after the pc is unplugged from everything.

BTW, the flash capacitors used in cameras, that store 300v, leaves nasty burn marks on your fingers if you happen to short those out. -.-

Also, you are sort of going back on what you said, it is known to most techs to NEVER EVER EVER wear an antistatic wrist strap attached to a pc when playing around with caps in the pc :-p
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Old 08-16-2010, 08:35 AM   #12 (permalink)
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Default Re: Computer Turns on but no screen?

The only capacitor I have ever seen that could possibly throw someone was a 1 farad capacitor. It was huge. The tiny capacitors on a motherboard are only just big enough to give you a little sting.
The capacitors in a power supply, however, can actually hurt you. NONE of these are going to throw you across the room.

Also, c0rr0sive is correct. Using the power button to discharge the caps on a motherboard is standard procedure. It opens the circuits and the motherboard tries to power on. The motherboard isn't pulling any amps from the power supply, so it discharges the capacitors safely by using their remaining charge to try and power on.

The reason I mentioned trying this is because even with the power off and the power supply unplugged, the capacitors can hold a charge for quite a while and the CMOS only barely sips power. It could last a few minutes, and it's a quick and simple procedure to discharge them with the power button if you're unsure.


EDIT: Also. What was this guy talking about anyway? Did he just feel the need to rant about how capacitors are dangerous? The capacitors in a TV are the huge variety I was talking about earlier. You're talking about from 0.5 up to 6 farads. This is enough not only to kill you but it will melt steel wires.

HOWEVER. This is not even close to the capacitors on a motherboard. The capacitors on your motherboard are somewhere on the order of 0.00035 farads, which is 350 micro farads. This is no where near enough to kill you. The static discharge from touching a door knob would hurt more, and the voltages in these tiny capacitors are so small that it wouldn't be enough to overcome the resistance of your skin.

Just sayin'. You said you were in school? Go read your book again.

TV = 25,000 volt 1f+ capacitor
Motherboard = 5 volt~ 350uf capacitor.
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Old 08-16-2010, 09:07 AM   #13 (permalink)
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Default Re: Computer Turns on but no screen?

Must say, all this information is surely informative lol...ya'll should like make a thread devoted to stuff like this, who knows, people might actually learn a lot like me . Also this thread has gone off track lol, a response from the thread starter could come in handy all now .
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Old 08-17-2010, 12:31 AM   #14 (permalink)
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Default Re: Computer Turns on but no screen?

Regarding the A+ procedures I'm still studying them.

I just saw the ordeal of dischargin capacitors. the Ones I'm used too, (even those in a PC monitor) can throw you on the ground easily. (I've seen it, and I've seen a close friend be put in an ambulance from bare skin contact onto one).

Perhaps my grandmothers PC was a special case when it had fried. But hers did fry when we attempted the power button.

Capacitors IME, aren't items to play around with. and you do want an anti-static band on when working with electronic ciruitry. Static Electricity can short circuits. It wont protect yourself from shock, however. (because once you make physical contact, you completed the "chain" in the circuit).

Everything I've learned working Electronics Technology, points to playing with capacitors as a big no no.
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Old 08-17-2010, 07:46 AM   #15 (permalink)
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Default Re: Computer Turns on but no screen?

Quote:
Originally Posted by ET/IT View Post
Regarding the A+ procedures I'm still studying them.

I just saw the ordeal of dischargin capacitors. the Ones I'm used too, (even those in a PC monitor) can throw you on the ground easily. (I've seen it, and I've seen a close friend be put in an ambulance from bare skin contact onto one).

Perhaps my grandmothers PC was a special case when it had fried. But hers did fry when we attempted the power button.

Capacitors IME, aren't items to play around with. and you do want an anti-static band on when working with electronic ciruitry. Static Electricity can short circuits. It wont protect yourself from shock, however. (because once you make physical contact, you completed the "chain" in the circuit).

Everything I've learned working Electronics Technology, points to playing with capacitors as a big no no.
This is the last I have to say on the subject. The original post by me was explaining how capacitors hold a charge and need to be discharged to fully clear the CMOS in some cases.
It was not about "playing around with" the capacitors.

Also, about your grandmothers PC; something else happened. You do not "fry" motherboards by pressing the power button. It's just not going to happen.

Also, about how a capacitor "can throw you on the ground". Gravity throws you to the ground. The electric shock disorients you.
If your friend was injured enough to go to the hospital then it was a large capacitor and he was foolish for not understanding how to properly handle such things.
I have been building, reconfiguring, and repairing circuits for over 10 years and I can tell you that no A+ book is going to say anything about replacing a capacitor being a "no no"

As a matter of fact, for a bit of fun. Take a small electrolytic capacitor around 15 or 30v. ANY school teaching A+ is going to have boxes of them laying around (you said you were in school right?).
It doesn't need to be a big capacitor, any will do, just make sure that it's electrolytic and around 15 or 20v. Connect it to one of those small 50 volt power supplies that come with bread boards attached to the bottom. You know the type right? Again this goes back to being in school.

Instead of hooking this capacitor up correctly to charge it, hook it up backwards, crank up the voltage, (make sure you're wearing protective goggles), and step away from the power supply.
Enjoy the pop.
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Old 08-17-2010, 09:55 AM   #16 (permalink)
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Quote:
Originally Posted by RichM499 View Post
Instead of hooking this capacitor up correctly to charge it, hook it up backwards, crank up the voltage, (make sure you're wearing protective goggles), and step away from the power supply.
Enjoy the pop.
Now this was fun, and because he said goggles, safe too!

Great educated info Rich and c0rr0sive.
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Old 08-17-2010, 01:22 PM   #17 (permalink)
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Quote:
Originally Posted by RichM499 View Post
This is the last I have to say on the subject. The original post by me was explaining how capacitors hold a charge and need to be discharged to fully clear the CMOS in some cases.
It was not about "playing around with" the capacitors.

Also, about your grandmothers PC; something else happened. You do not "fry" motherboards by pressing the power button. It's just not going to happen.

Also, about how a capacitor "can throw you on the ground". Gravity throws you to the ground. The electric shock disorients you.
If your friend was injured enough to go to the hospital then it was a large capacitor and he was foolish for not understanding how to properly handle such things.
I have been building, reconfiguring, and repairing circuits for over 10 years and I can tell you that no A+ book is going to say anything about replacing a capacitor being a "no no"

As a matter of fact, for a bit of fun. Take a small electrolytic capacitor around 15 or 30v. ANY school teaching A+ is going to have boxes of them laying around (you said you were in school right?).
It doesn't need to be a big capacitor, any will do, just make sure that it's electrolytic and around 15 or 20v. Connect it to one of those small 50 volt power supplies that come with bread boards attached to the bottom. You know the type right? Again this goes back to being in school.

Instead of hooking this capacitor up correctly to charge it, hook it up backwards, crank up the voltage, (make sure you're wearing protective goggles), and step away from the power supply.
Enjoy the pop.
We've already done stuff like that.

Even burnt the bread boards. You do the resistor one? When you get a 500k ohm resistor, connect it too a 50v PSU, and then burn it up? For some odd reason, i kinda like burning them.
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Old 08-17-2010, 01:48 PM   #18 (permalink)
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Default Re: Computer Turns on but no screen?

Back on topic please. -.-
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