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How to Jump Dell Dim 8400 Motherboard

Last response: in Motherboards
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October 12, 2010 5:50:17 AM

I'm looking for some detailed specs for a Dell Dimension 8400 motherboard (my friend's system). Specifically, the system for no apparent reason could not be powered on.

The power supply checks out pretty decent, voltages are within specs. So I figure either the power switch or motherboard is bad.

Most of the generic instructions available for jumping motherboards refer to a two-pin momentary switch connection labeled PWR, or PWR_BTN. The problem is, on this board, there's a "front-panel connector" with around 30 or so pins, and a ribbon cable going to the front panel lights, power switch, etc. The power switch itself is fairly inaccessible, and I don't see any instructions provided showing how to remove it.

The cable can be easily removed from the motherboard. Where can I find out which of the 30 pins are the correct ones for starting the power-on sequence? Just my luck, the Dell Support Forum website has been down the last few days.

Thank you for any ideas!
a b V Motherboard
October 12, 2010 5:58:32 AM

If you cant identify or get to the pwrsw pin, look for the grey wire on the 20+4pin connector, short it to a black wire and that in effect is 'pressing the power switch'
**Edit** As always ofc, be careful playing with electricity and things :) **
Moto
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a b V Motherboard
October 13, 2010 12:06:20 PM

Motopsychojdn said:
If you cant identify or get to the pwrsw pin, look for the grey wire on the 20+4pin connector, short it to a black wire and that in effect is 'pressing the power switch'

You meant "Green" , right ?
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a b V Motherboard
October 13, 2010 6:02:05 PM

Thanks, Dell :) 
My brain had the grey wire flagged up because it's voltage jumps to power the cpu, I did mean green though, Sorry for misleading you Op (albeit unintentionally)
Moto
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October 14, 2010 6:05:58 AM

Well, I tried Moto's suggestion on a working Dell 8200 system-- I shorted the green to a black, and when the cord was plugged in, the PSU fan started up, but not the motherboard.

When I then pressed the power button, the system started to POST, the drives started up, like normal.

So I'm thinking there must be another missing factor to simulate the button press.
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October 14, 2010 10:33:19 AM

I have encountered this problem - the wire connecting the front switched to your motherboard is not working you have to replaced this. There are the 6pin and the 24 pin rarely the pins do not connect well with the motherboard. I fix this by replacing the switched (I make another switch). I disassemble everything and use another supply and it work. careful thought.
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October 14, 2010 2:45:57 PM

Yes, the control board and cable setup is similar to the picture Moto posted.

I will have to post back on this next week. Thanks for the comments.
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November 3, 2010 4:20:54 AM

With the 24-pin connector disconnected from the MB, and with the PS_ON signal (green) grounded, the PSU's fan turned on, the 24-pin voltages were good, and there was good voltage on the drive power connectors. That had led me to think either the power switch or motherboard had the problem.

But when connected back to the MB, there was no fan, and no voltage registering on the drive power connectors, even with PS_ON grounded.

That didn't seem right to me, so I finally got a hold of a known-good PSU, hooked it up to the system, and everything worked fine, power button and all.

I have ordered a new 400W power supply.
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a b V Motherboard
November 3, 2010 6:43:52 AM

Cool, Glad you got sorted ok man, :) 
Moto
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November 14, 2010 4:21:42 AM

Best answer selected by mosh112.
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a b V Motherboard
November 14, 2010 8:44:06 AM

Thank you for B.a.
new psu all good I hope?
Moto
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a c 135 V Motherboard
November 14, 2010 12:36:09 PM

This topic has been closed by Maziar
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