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#1
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Does ANYONE know this PSU answer....
I wish to try a number of PSU's for operation without having to put em in a
PC. I gather there are 2 terminals to short out on the power cable loom to the mobo, so fooling it in to thinking it is connected to the mobo, but which terminals? |
#2
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"TyQuAnDo" wrote in message
... I wish to try a number of PSU's for operation without having to put em in a PC. I gather there are 2 terminals to short out on the power cable loom to the mobo, so fooling it in to thinking it is connected to the mobo, but which terminals? Connect pin 14 (green) to ground (any black wire). Google is really good for this type of question. Gareth |
#3
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"TyQuAnDo" wrote in message ... | I wish to try a number of PSU's for operation without having to put em in a | PC. | | I gather there are 2 terminals to short out on the power cable loom to the | mobo, so | fooling it in to thinking it is connected to the mobo, but which terminals? Make sure you put a load on the PSU you're testing. |
#4
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Thanks all
I just want to flip them on really to see if there is any life before fitting them in a case and then finding they are dead or the fans make a noise, so I shouldn't think I will need 'a load' for a few seconds will I? "Bishoop" wrote in message ... "TyQuAnDo" wrote in message ... | I wish to try a number of PSU's for operation without having to put em in a | PC. | | I gather there are 2 terminals to short out on the power cable loom to the | mobo, so | fooling it in to thinking it is connected to the mobo, but which terminals? Make sure you put a load on the PSU you're testing. |
#6
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Tom? Where are you when we need you
If you do short the terms, and if the PSU is weak or older, it can go "POOF' in a second "TyQuAnDo" wrote in message ... I wish to try a number of PSU's for operation without having to put em in a PC. I gather there are 2 terminals to short out on the power cable loom to the mobo, so fooling it in to thinking it is connected to the mobo, but which terminals? |
#7
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TyQuAnDo wrote:
Thanks all I just want to flip them on really to see if there is any life before fitting them in a case and then finding they are dead or the fans make a noise, so I shouldn't think I will need 'a load' for a few seconds will I? Most ATX power supplies will not start without a minimum load. They usually need about one amp drawn, but are usually not particular whether it's the +5V or +12V. You can use a power resister (1A @ 5V = 5ohm/5W resistor), but an automobile tail lamp works fine, and is a lot easier to find. It also lites up to show the supply is working. A hard drive attached to the PS will also draw enough current to allow it to start. As has been noted, any real test would involve the measurement of all voltages under rated loads. Some better supplies have fans that speed up as the temperature in the PS increases, so you can't judge the fan noise by the unloaded, (cool), fan RPMs. Most, however have a single speed fan, and a cheap one at that! Virg Wall -- A foolish consistency is the hobgoblin of little minds,........ Ralph Waldo Emerson (Microsoft programmer's manual.) |
#8
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"TyQuAnDo" wrote in message
I wish to try a number of PSU's for operation without having to put em in a PC. I gather there are 2 terminals to short out on the power cable loom to the mobo, so fooling it in to thinking it is connected to the mobo, but which terminals? One of the wires in the 20-pin Molex connector going from the power supply to the motherboard is PS-ON. When this signal is open (i.e., disconnected), the power supply will shut off. When PS-ON is pulled TTL high (over 2.0 volts), the power supply shuts off. When PS-ON is pulled TTL low (under 0.8 volts), the power supply's other outputs turn on along with the fan. Whether turned on or off, the power supply always supplies 5 volts to the motherboard for circuitry that must continue to be powered even when the power supply is "off", like for "Wake on event" settings in the BIOS. That is why you need to yank the power cord from the back of the power supply when changing PCI cards. Another user remarked that a load needs to be on the power supply, like hooking up a hard drive. I have read that turning on a switching power supply without a load can ruin it, that it will burn up if tested without a load, and that's why they do not turn on unless the 20-pin Molex connector is attached to a motherboard (i.e., PS-On pin 14 is pulled TTL low). However, not measuring the load (amperage) capacity of the taps means you have no idea of the quality of output capable by the power supply; checking voltages doesn't indicate capacity. Lots of power supplies will claim that they will put out, say, 350 watts but actually cannot put out more than two-thirds of that. You might want to review the Tom's Hardware articles about power supplies at: http://www6.tomshardware.com/howto/20021021/index.html http://www6.tomshardware.com/howto/20030609/index.html http://www.cluboc.net/reviews/index.htm#power (and a Google search will turn up more reviews) You might be able to decipher how to build Tom's test rig from its pictures and description at http://www6.tomshardware.com/howto/2...pplies-03.html. They really don't provide a how-to-build tutorial on all the parts you need and a sample layout of the PCB that you'll have to etch. There's no way to test that capacitors are defective and will start leaking since that usually occurs after a long time. But after testing loads at the max ratings per tap continuously for a couple days you might then want to pop the cover off and take a look inside. Note that a multimeter (volts & amps) won't tell you how much regulation will degrade under high load. You'll need an scope to look at the ripple. If you are not looking to qualify the claimed capacity or quality of the outputs for the PSU, and all you want is an OK-notOK check, I suppose you could get something simplistic like the Antec ATX Power Supply Tester for around $10 to $15 USD. CompUSA has one (Powmax; http://www.powmax.com/Power%20Tester.htm) for $15. I believe the Antec tester only checks the +5V output using its 20-pin Molex connector (but says it has leads to test +12V and +3.3V) while the Powmax tests Full test on +3.3V, +5V, +12V, -5V, -12V, and +5Vsb outputs concurrently. However, with either of these units, you still need to get a good multimeter. Of course, you go industrial and get something like the http://www.prodigit.com/e3600.htm for lots and lots of money, so spending the money on something like Tom's tester rig would be a lot cheaper but requires you be handy with a soldering iron, PCB etching, parts selection, and basic electronic repair and testing, and buy a couple other test equipment like a digimeter that can measure high currents. -- __________________________________________________ __________ ** Share with others. Post replies in the newsgroup. ** If present, remove all "-nix" from my email address. __________________________________________________ __________ |
#9
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On Sun, 24 Aug 2003 17:12:14 +0100, "TyQuAnDo"
wrote: Thanks all I just want to flip them on really to see if there is any life before fitting them in a case and then finding they are dead or the fans make a noise, so I shouldn't think I will need 'a load' for a few seconds will I? Writing in generalizations only, a cheap/junk power supply "might" be destroyed by power-on without a load. It's not likely these days, but possible. A moderately better, consumer/PC grade power supply won't damage itself, but may not run without a load attached to the +5V rail. You should always assume you need a load on the 5V rail. A hard drive is less than the typical 2A load the manufacturer spec requires, but it generally enough. A better, high-end power supply may or may not need a load on the 5V rail, it can vary based on the target system/market. It WILL monitor 3V rail. Some power supplies monitor the 3V rail internally, but sometimes externally instead, rather through the 3V sense line on the motherbaord connector/leads. The 3V sense line might be paired with a 3V supply line on the same pin, so there's 3 3V conductors instead of only 2, total, going to the motherboard via the main ATX connector. By doing that you already have the sense line connected to the supply line. This 3V sense line is pin 11. The manufacturer can choose to put ONLY the sense line on pin 11, or place BOTH the sense line and a 3V rail line on pin 11, which means two physical wires at pin 11. All too often I see this point neglected, and as a result a perfectly good power supply might be declared dead by conventional (power-on shorting and 5V load) methods of testing. In order to keep one of these PSU (with only the sense used on pin 11) powered on, even for more than a fraction of a second, you MUST also connect the 3V sense line to the 3V rail, one of the other 3V pins. When a power supply is connected to the motherboard this sense pin is connected to the rail, but not when the connector is removed. A load on the 3V rail can also be required but it's even less common, and placing a load on the 3V rail wouldn't (by itself) accomplish this requirement to have the 3V sense line connected. So in summary, yes, you need a load. The far easiest way to test a power supply isn't to fool with all these external loads and shorting power-on-to-ground, etc.. the easiest way is just to keep an old/junk motherboard lying around with a power switch connected. I actaully soldered a switch onto an old board I have here. If you don't care about seeing the motherboard hardware monitor/BIOS reported voltages then this old motherboard doesn't even need to have ANY other parts plugged into it, no cpu or memory, video card, etc... a bare motherboard with a power switch attached will turn on a motherboard. Even motherboards that die from "most" causes, except something shorting out, are still functional to turn on a power supply and keep it running. Dave |
#10
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TyQuAnDo wrote:
I just want to flip them on really to see if there is any life before fitting them in a case and then finding they are dead or the fans make a noise, so I shouldn't think I will need 'a load' for a few seconds will I? Often, yes. The PSU will shut down immediately without it. |
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