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 Post subject: Changing LEDs in PSU
PostPosted: Tue Apr 07, 2009 4:42 pm 
Little Foot
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I have a OCZ GameXStream Power Supply and I'm wondering how to discharge the capicators so i dont kill myself when im changing the leds in the unit from blue to green to match my whole AMD colour scheme mod.


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PostPosted: Tue Apr 07, 2009 5:39 pm 
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with PSU in computer and everything hooked up (mobo, drives etc), unplug PSU cord from wall. hold power button on computer down for like 5-10 seconds. it will probably start to fire up for a second or two, then die. all LEDs on the mobo (if it has any) should be out at this point. remove PSU and have fun.


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PostPosted: Tue Apr 07, 2009 6:44 pm 
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just an FYI, but this will clear your BIOS, so any ocing will have to be redone


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PostPosted: Wed Apr 08, 2009 3:17 am 
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Grim Tuesday wrote:
just an FYI, but this will clear your BIOS, so any ocing will have to be redone


?

thats what your CMOS battery is for, holding BIOS data when no power is present.

I fully discharge my PSUs any time I change components, never had BIOS data reset on me.

is this some new thing? like some BIOSs will revert to "fail safe" settings if there is no successful POST x times in a row? I had a mobo that would do that but it needed a "no POST" condition 3 times before resetting.


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PostPosted: Wed Apr 08, 2009 3:40 am 
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Grim Tuesday wrote:
just an FYI, but this will clear your BIOS, so any ocing will have to be redone
No it won't.


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PostPosted: Wed Apr 08, 2009 3:42 am 
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CharBroiled wrote:
I fully discharge my PSUs any time I change components, never had BIOS data reset on me.
I would still warn the OP that even though the caps should be close to discharged you still need to be STUPIDLY careful inside your PSU. You can never be 100% sure that the caps have been fully discharged.

Although I would assume that they'd be damn close. Caps don't indefinitely hold their charge so waiting an hour or so after wouldn't hurt to be sure.


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 Post subject:
PostPosted: Wed Apr 08, 2009 5:27 am 
Little Foot
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Thanks...does anyone have an idea what type of LEDs on in the power supply? I would assume 3V is a standard.


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PostPosted: Wed Apr 08, 2009 6:16 am 
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DrCoolP wrote:
Thanks...does anyone have an idea what type of LEDs on in the power supply? I would assume 3V is a standard.
Maybe? I don't know. You will have to look at it. They might be 1.5v?


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PostPosted: Wed Apr 08, 2009 11:41 am 
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CrashTECH wrote:
I would still warn the OP that even though the caps should be close to discharged you still need to be STUPIDLY careful inside your PSU. You can never be 100% sure that the caps have been fully discharged.

Although I would assume that they'd be damn close. Caps don't indefinitely hold their charge so waiting an hour or so after wouldn't hurt to be sure.


good point. Ill do that if the question comes up again.


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PostPosted: Wed Apr 08, 2009 5:03 pm 
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With regard to the PSU and cahrged capacitors. Actually there are only two capacitors in a PSU that can ruin your day or possibly your life.

They look much like this:

Image

Note their rated working voltage of 200 Volts. Now here is how they look in an actual PSU circuit, this is just the front end lines side with the rest chopped off as it would break tables.

PSU Front End:

Image

The pictured capacitors are actually labeled C5 and C6 in the schematic drawing. Note they are in a series configuration of sorts. Each cap will charge to a peak value of the mains voltage or as configured a peak value of 120 X 1.414 = 170 Volts or combined about 340 Volts.

Now note two resistors beside those caps labled R2 and R3. Those 220 K Ohm resistors serve as Bleeder Resistors" to discharge C5 and C6.

Anytime the PSU is plugged in and the PSU power switch is ON that front end has charged capacitors. When mains power is removed the discharge path for the caps is the bleeders.

Actually those two caps discharge pretty slow even with bleeders. How quick? Calculate the RC Time Constant. Roughly in less that 20 min.The rate of charge and discharge is log and not a linear function.

Note just beyond the bleeder resistors two lines drop down off the picture. Those lines feed the supply for the 5 Volt SB (Stand By) supply which is necessary for the PSU to start. The front panel push button uses that power to start the PSU.

Actually once mains power is removed within a few seconds pressing the front panel power button won't do anything.

I guess if we were really curious we could chart some of this stuff? Might be interesting?

Generally speaking it is safe to work on a PSU despite claims otherwise. However unless someone is real comfortable in there caution including over cautious is the best road to take. Hey, better to err on the side of safety that have a shocking experience. :shock:

Edited to fix my suck math!

Ron


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 Post subject:
PostPosted: Thu Apr 09, 2009 10:55 am 
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Reloadron wrote:
With regard to the PSU and cahrged capacitors. Actually there are only two capacitors in a PSU that can ruin your day or possibly your life.

[.. SNIP...]

Now note two resistors beside those caps labled R2 and R3. Those 220 K Ohm resistors serve as Bleeder Resistors" to discharge C5 and C6.

Anytime the PSU is plugged in and the PSU power switch is ON that front end has charged capacitors. When mains power is removed the discharge path for the caps is the bleeders.

Actually those two caps discharge pretty slow even with bleeders. How quick? Calculate the RC Time Constant. Roughly in less that 20 min.The rate of charge and discharge is log and not a linear function.

Note just beyond the bleeder resistors two lines drop down off the picture. Those lines feed the supply for the 5 Volt SB (Stand By) supply which is necessary for the PSU to start. The front panel push button uses that power to start the PSU.

Actually once mains power is removed within a few seconds pressing the front panel power button won't do anything.

I guess if we were really curious we could chart some of this stuff? Might be interesting?

Ron


that tracks with what Ive noticed on my rigs. if I wait more than around 5 to 10 minutes after unplugging or switching off the PSU the power switch will not do anything. also about that time the LEDs on the mobo are out anyway. I figured either parasitic draw from the mobo or bleeders were the reason.

I wondered if there were bleeders for the caps. Old Skool engineering always had them on any high voltage caps but I wasnt sure about newer PSUs.


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 Post subject:
PostPosted: Thu Apr 09, 2009 12:33 pm 
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Hey Ron: If you turn off the PSU, leave it plugged in, and press the power button while the board's lights are still on, doesn't that instantly bleed the caps without the bleeders?
------------------------------------
Just an FYI of my own: Touching the caps won't do anything. Touching the leads will. Since the boards are screwed in with a plastic cover underneath, you should be better off if you don't do all of this and just don't mess with the board IMO.

Fans can be found to have pins, but usually only if you're lucky. So...you might have to un-solder the leads to put in the other fan.


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 Post subject:
PostPosted: Thu Apr 09, 2009 2:10 pm 
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I knew I shouldn't have posted while drinking beers.

We won't revisit RC time constants but something interesting was brought up so we will hit on that.

Most new motherboards have that now infamous LED on them. Even when the system is off that LED just sits there glowing. Within a PSU there are actually two power supplies each with their own transformer(s). WE have the main power and we have a small transformer off the mains power (after rectification) for the 5 Volt Stand By power, That 5 V SB is what is used to actually turn on the main power supply. The motherboard uses logic to get things going. The presence of that 5 Volt SB power is indicated on many motherboards by that little LED.

We can pretty much figure that when we remove mains power to the system either by the rear switch or yanking the plug that when that LED extinguishes any charge on the HV Caps is gone. Well below where they will hurt you. Also, once the LED is out, pushing the front panel power button won't do much of anything.

Chumly makes a point I failed to mention. Touching the caps won't do anything, hell you could lick them when they are charged. However. where the leads extend out the bottom is where you don't want to touch. Then bad shit happens. Also, yes, if the 5 V SB is still there after power removal and the Front Panel power button is pressed it will discharge the caps faster. However, it is not a method I like to use.

Charbroiled brings up another point and yes, any decent PSU (even the piece of crap I photographed) uses bleeder resistors as those seen in the schematic I posted.

I have a few things going tomorrow but as we get into the weekend maybe I'll find time to plot an actual PSU in a system and look at the high voltage and time the discharge on a plot.

Ron


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 Post subject:
PostPosted: Thu Apr 09, 2009 3:50 pm 
Boy in Black
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Roger...I'm now licking all of my capacitors on Ron's say so. :twisted:

LOL...just having fun!


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 Post subject:
PostPosted: Thu Apr 09, 2009 4:09 pm 
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Chumly wrote:
Roger...I'm now licking all of my capacitors on Ron's say so. :twisted:

LOL...just having fun!


Remove a cap and fully charge it. Then urinate on it for a cool experience. Be sure to piss on the leads. Don't worry as urine is acidic and conductive so therefore should discharge it.

Ron


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