If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Safe Power Supply Tinkering
My power supply has just started to make ominous grinding noises, so it
looks like I'll want to whip out the fan and replace it before the thing melts on me. However, I have to admit that I'm terrified of opening the it, as I gather you can get quite a nasty (potentially fatal) shock if you don't know what you're doing. What precautions should I take before opening it up? Please err on the side of paranoia in your advice; I only need to do this once and I *really* don't want to go to hospital over it :-) Ewan |
#2
|
|||
|
|||
Ewan Sinclair wrote:
My power supply has just started to make ominous grinding noises, so it looks like I'll want to whip out the fan and replace it before the thing melts on me. However, I have to admit that I'm terrified of opening the it, as I gather you can get quite a nasty (potentially fatal) shock if you don't know what you're doing. What precautions should I take before opening it up? Please err on the side of paranoia in your advice; I only need to do this once and I *really* don't want to go to hospital over it :-) Just leave it unplugged over night. That is more than plenty of time. |
#3
|
|||
|
|||
Before you open it make sure you earth yourself by touching the side of the
case. Steve Gill "ric" wrote in message ... Ewan Sinclair wrote: My power supply has just started to make ominous grinding noises, so it looks like I'll want to whip out the fan and replace it before the thing melts on me. However, I have to admit that I'm terrified of opening the it, as I gather you can get quite a nasty (potentially fatal) shock if you don't know what you're doing. What precautions should I take before opening it up? Please err on the side of paranoia in your advice; I only need to do this once and I *really* don't want to go to hospital over it :-) Just leave it unplugged over night. That is more than plenty of time. |
#4
|
|||
|
|||
Ewan Sinclair wrote:
What precautions should I take before opening it up? Please err on the side of paranoia in your advice; I only need to do this once and I *really* don't want to go to hospital over it :-) There are two capacitors in the PS that are charged to about 320 V DC (in series). These each have "bleeder" rsistors, to insure that they will discharge in a few minuites. Actually, about five minutes should be enough for them to discharge to a very safe value. If you're really paranoid, unplug it overnight. Be careful you don't burn yourself if soldering the fan wires! Virg Wall -- A foolish consistency is the hobgoblin of little minds,........ Ralph Waldo Emerson (Microsoft programmer's manual.) |
#5
|
|||
|
|||
On Mon, 03 Nov 2003 22:03:04 GMT, "Ewan Sinclair"
wrote: My power supply has just started to make ominous grinding noises, so it looks like I'll want to whip out the fan and replace it before the thing melts on me. However, I have to admit that I'm terrified of opening the it, as I gather you can get quite a nasty (potentially fatal) shock if you don't know what you're doing. What precautions should I take before opening it up? Please err on the side of paranoia in your advice; I only need to do this once and I *really* don't want to go to hospital over it :-) Ewan After posting "misc." advice myself and still wondering exactly how long someone should wait till opening their power supply, I have now begun this test with all power supplies I open, again repowering them and watching the voltage drop... The voltage on every PC power supply I've tested so far, about 10 so far, is below 50V in less than 60 seconds. 50V from a UNPLUGGED power supply is not enough to do more than suprise you, and by the time you've unscrewed and unplugged one installed in a PC, the voltage is too low to even produce a spark. Granted, there might be some really really badly designed power supply out there that have no bleeder resistors, at some point in the furture I will disconnect those and retest a power supply with atypically large primary capacitors to see just how long it takes for them to drain, but of course it would be good to get a general consensus on the exactly voltage level we can consider "safe" for someone looking to grab hold of a capactor and see what happens. Even so, an ATX power supply will still power the control circuit and 5VSB as long as it can before voltage drop shuts it down, so there is still a safeguard to drain the power quickly.... A power supply doesn't actually "know" it's plugged into AC power or not, it works until it can't maintain the voltage then shuts off, after draining most of it's capacitor-stored energy. To more directly answer your question, there is very little danger after a few minues. Dave |
#6
|
|||
|
|||
There are two capacitors in the PS that are charged to about 320 V DC (in
series). These each have "bleeder" rsistors, to insure that they will discharge in a few minuites. Actually, about five minutes should be enough for them to discharge to a very safe value. If you're really paranoid, unplug it overnight. Does it discharge best when unplugged, or does it like to have a ground wire to bleed down? if so, should I leave the little switch on the back on, or off? Be careful you don't burn yourself if soldering the fan wires! Heh, thanks for the warning :-) Ewan |
#7
|
|||
|
|||
Ewan Sinclair wrote:
There are two capacitors in the PS that are charged to about 320 V DC (in series). These each have "bleeder" rsistors, to insure that they will discharge in a few minuites. Actually, about five minutes should be enough for them to discharge to a very safe value. If you're really paranoid, unplug it overnight. Does it discharge best when unplugged, or does it like to have a ground wire to bleed down? if so, should I leave the little switch on the back on, or off? Be careful you don't burn yourself if soldering the fan wires! Heh, thanks for the warning :-) Ewan See kony's posting for some actual numbers. The bleeder resistors are directly across each capacitor. It matters not what you do externally. By the time you get the PS out of the case, and the cover removed, the voltage will be low enough. Even with open bleeder resistors, electrolytic capacitors have an internal shunt resistance that would not let them hold a charge for "days" as the rumors go. The most dangerous voltage in most electronic equipment is the line voltage. In the old AT power supplies, it was brought right up front in the computer case. Even before you've unpluged an ATX PS there are no dangerous voltages in the case. Be careful of sharp edges!;-) Virg Wall -- A foolish consistency is the hobgoblin of little minds,........ Ralph Waldo Emerson (Microsoft programmer's manual.) |
#8
|
|||
|
|||
"Ewan Sinclair" wrote in message ... My power supply has just started to make ominous grinding noises, so it looks like I'll want to whip out the fan and replace it before the thing melts on me. However, I have to admit that I'm terrified of opening the it, as I gather you can get quite a nasty (potentially fatal) shock if you don't know what you're doing. What precautions should I take before opening it up? Please err on the side of paranoia in your advice; I only need to do this once and I *really* don't want to go to hospital over it :-) Ewan Is this a quality psu, if not junk it and buy a good one, Antec solution series (smartpower) is a good start. http://www.antec-inc.com/pro_p_solutionpw.html Lane |
#9
|
|||
|
|||
Well, I replaced my fan and I'm not dead or injured, so thanks for the
advice everyone :-) Just in case I'll be doing this again though..... Would shorting one of the positive leads to ground on the +5, 3.3 or 12v pins through a resistor guarantee an empty pair of caps on the offchance that the PSU was so cheap that they didn't put bleeder resistors on? Ewan |
#10
|
|||
|
|||
Ewan Sinclair wrote:
Well, I replaced my fan and I'm not dead or injured, so thanks for the advice everyone :-) Just in case I'll be doing this again though..... Would shorting one of the positive leads to ground on the +5, 3.3 or 12v pins through a resistor guarantee an empty pair of caps on the offchance that the PSU was so cheap that they didn't put bleeder resistors on? No. |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Grinding Power Supply? | PawsForThought | General | 37 | October 9th 03 04:33 PM |
Power Supply question | John Smith | General | 5 | September 27th 03 04:42 PM |
How can I make motherboard to restart after power loss automatically? | Amiran | General | 1 | September 24th 03 11:35 PM |
Power Supply on its way out? | w_tom | General | 5 | July 31st 03 03:43 PM |
Power Supply Gone Bad? | John | General | 4 | July 22nd 03 08:42 PM |