My PSU was not up to snuff to power the gtx470 i just added to my computer. Its a Dell vostro 200. The outgoing psu was a logisys, the incoming a corsair cx600. The fans kick for a second and the mobo standby light comes on but it won't boot. Hook up the old psu and it boots fine. The only thing I see different is the old one had a white wire going to the -5v plug on the mobo connector and the new one does not, but that connection seems to be obsolete with atx 2.0. The motherboard is a foxcon g33m02 if that helps any.
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New PSU won't turn computer on
- Thread starter Mizzery
- Start date
- Joined
- Jul 14, 2002
I'd be very surprised if a 600W Corsair couldn't run anything that a Logisys could, even a Logisys rated for much more power.
I've had several new Corsair CX430s (by CWT) and some Antec 620W Neo Ecos (Seasonic) act that way when brand new, despite them all passing the bent paperclip test (ground green wire to turn on PSU without motherboard). But the motherboards ran fine after I reseated the power connectors several times.
I've had several new Corsair CX430s (by CWT) and some Antec 620W Neo Ecos (Seasonic) act that way when brand new, despite them all passing the bent paperclip test (ground green wire to turn on PSU without motherboard). But the motherboards ran fine after I reseated the power connectors several times.
- Joined
- Mar 29, 2003
Do you have the manual or can you find it?
Is there a jumper that needs to be set?
You had a atx1.0 PS...is the mobo compliant with atx2.0 ?
According to this: it is not atx2.0
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Shouldn't matter. I have 10+ year old mobo's running on current gen PSU's.
Proprietary Dell wiring perhaps?, or just plain DOA PSU.
- Thread Starter
- #5
Well I did the paperclip test. It came on. I had a new cpu come in the mail today so I swapped that in and then tried the corsair psu with it. Magically it worked today. Now to get everything back together neatly.
Edit: Putting everything back together i hooked up a fan I had running at 7v. Apparently that is what the psu didn't like. I did try it without the fan last night but not sure if i did things in the same order. Either way its working and my computer doesn't smell like noxious chemicals when I fold on the gpu now
Edit: Putting everything back together i hooked up a fan I had running at 7v. Apparently that is what the psu didn't like. I did try it without the fan last night but not sure if i did things in the same order. Either way its working and my computer doesn't smell like noxious chemicals when I fold on the gpu now
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- Joined
- May 10, 2009
7V mod is actually a pretty terrible thing to do to your computer IMO.
The 5V rail on the PSU is output only. Electricity CANNOT flow into it.
So what you're doing, essentially, is feeding 12V minus the fan's voltage drop to the 5V components. You're not grounding to the 5V rail, you're "grounding" to the 5V INPUT pins on your hard drives, motherboard, etc. Things you don't want to feed 12V to!
If the fan flows enough current it will start dragging the rail voltage up, the higher the rail voltage gets the less current the PSU will put into the 5V rail, so instead of nice smooth PSU based 5V you have a ripple filled, unfiltered, disaster of a 5.xV coming out of the fan.
Take it far enough and the PSU will shut down due to OVP on the 5V rail.
Or, of course, something will die, or fail, or crash.
IMO a good PSU should sense something going terribly terribly wrong when the 5V starts going up without its help, and shut down.
The 5V rail on the PSU is output only. Electricity CANNOT flow into it.
So what you're doing, essentially, is feeding 12V minus the fan's voltage drop to the 5V components. You're not grounding to the 5V rail, you're "grounding" to the 5V INPUT pins on your hard drives, motherboard, etc. Things you don't want to feed 12V to!
If the fan flows enough current it will start dragging the rail voltage up, the higher the rail voltage gets the less current the PSU will put into the 5V rail, so instead of nice smooth PSU based 5V you have a ripple filled, unfiltered, disaster of a 5.xV coming out of the fan.
Take it far enough and the PSU will shut down due to OVP on the 5V rail.
Or, of course, something will die, or fail, or crash.
IMO a good PSU should sense something going terribly terribly wrong when the 5V starts going up without its help, and shut down.
- Thread Starter
- #8
That makes a lot of sense. I'm glad to know corsairs lower end line has such protections. Would limiting the fan with a resistive load be ok or should I look into a pwm controller? It specs to draw close to an amp at 12v.
- Joined
- May 10, 2009
Resistive works fine as long as you use a resistor rated for enough wattage. That's a nice resistive load, the friendliest kind
Whether a resistor will work for you largely depends on the voltage you want to end up with at the fan and the amperage of the fan. As a very crude example, if you want to have 7V for the fan you have to take the 12V rail and get rid of 5V of it. Let's say the fan is rated at 0.24 amps, that's reasonable for a noisy-but-sane generic computer fan.
To get wattage we take voltage (5V is being consumed/dropped by the resistor) and multiply by amperage (the 0.24a fan rating), giving us 5 * 0.24 = 1.2 watts. If you use a "standard" 1/4w resistor it's going to get hot, smell bad, char, smell really bad, smoke and smell bloody horrible, and then eventually die. A good rule of thumb is to use a resistor rated for 2x the actual load, so we want a 2.4w resistor. Odds are you'll need to round up to a 3w or 5w resistor. These aren't cheap like the lower ratings, but they don't cost too much. A buck or two maybe.
Now like I said this is a crude example, in reality a fan that draws 0.24a at 12V will draw less at 7V, and who knows what your fan is rated at (your fan does though, it should be printed on the hub sticker. If it is rated in watts divide by 12 to get amps), but it'll aim you in the right direction.
To choose a resistor to drop a given voltage, find out what the fan is rated for first, 0.24a in my example above.
Then figure out how much voltage you want to drop, 5V above.
Then take voltage and divide by amperage, this gives you the resistance in ohms. 5 / 0.24 = 20.83ohms. Your odds of finding a 20.8 ohm resistor are low (for a decent price, anyway), so round up, 22Ohm out to work.
If you want to run at 10v and have a 0.2 amp fan, 2V drop / 0.2 amps = 10 ohms, and 2V * 0.2A = 0.4 watts, so a 1 watt resistor would be great.
Alternatively a PWM fan will accept a very low power signal for speed control, and do it rather more efficiently.
Whether a resistor will work for you largely depends on the voltage you want to end up with at the fan and the amperage of the fan. As a very crude example, if you want to have 7V for the fan you have to take the 12V rail and get rid of 5V of it. Let's say the fan is rated at 0.24 amps, that's reasonable for a noisy-but-sane generic computer fan.
To get wattage we take voltage (5V is being consumed/dropped by the resistor) and multiply by amperage (the 0.24a fan rating), giving us 5 * 0.24 = 1.2 watts. If you use a "standard" 1/4w resistor it's going to get hot, smell bad, char, smell really bad, smoke and smell bloody horrible, and then eventually die. A good rule of thumb is to use a resistor rated for 2x the actual load, so we want a 2.4w resistor. Odds are you'll need to round up to a 3w or 5w resistor. These aren't cheap like the lower ratings, but they don't cost too much. A buck or two maybe.
Now like I said this is a crude example, in reality a fan that draws 0.24a at 12V will draw less at 7V, and who knows what your fan is rated at (your fan does though, it should be printed on the hub sticker. If it is rated in watts divide by 12 to get amps), but it'll aim you in the right direction.
To choose a resistor to drop a given voltage, find out what the fan is rated for first, 0.24a in my example above.
Then figure out how much voltage you want to drop, 5V above.
Then take voltage and divide by amperage, this gives you the resistance in ohms. 5 / 0.24 = 20.83ohms. Your odds of finding a 20.8 ohm resistor are low (for a decent price, anyway), so round up, 22Ohm out to work.
If you want to run at 10v and have a 0.2 amp fan, 2V drop / 0.2 amps = 10 ohms, and 2V * 0.2A = 0.4 watts, so a 1 watt resistor would be great.
Alternatively a PWM fan will accept a very low power signal for speed control, and do it rather more efficiently.
- Joined
- Jul 14, 2002
I've found that fans typically draw about half their rated amps.Resistive works fine as long as you use a resistor rated for enough wattage. That's a nice resistive load, the friendliest kind
To choose a resistor to drop a given voltage, find out what the fan is rated for first, 0.24a in my example above.
Then figure out how much voltage you want to drop, 5V above.
Then take voltage and divide by amperage, this gives you the resistance in ohms. 5 / 0.24 = 20.83ohms. Your odds of finding a 20.8 ohm resistor are low (for a decent price, anyway), so round up, 22Ohm out to work.
If you want to run at 10v and have a 0.2 amp fan, 2V drop / 0.2 amps = 10 ohms, and 2V * 0.2A = 0.4 watts, so a 1 watt resistor would be great.
Alternatively a PWM fan will accept a very low power signal for speed control, and do it rather more efficiently.
Some old Leadman/Raidmax/Powmax used nothing but a thermistor rated 50 ohms (at 25 Celcius) in series with the fan's +12V to control its speed. The thermistor was epoxied to one of the donut coil output filters.
