How to Jump Dell Dim 8400 Motherboard

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How to Jump Dell Dim 8400 Motherboard

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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 flat 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?

Thank you for any ideas!

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  • The Dell front panel connector is a proprietary and undocumented connector.  Dell has never released any info on these. 

    I've seen one or two posts from users that have traced out all the connections however the connections can vary from one model to another so unless you could find an 8400 specific user wiring diagram it may not do you any good.

    I am not a Dell Employee

    Dell forum member since 2002

    Home Built PC with Gigabyte GA-Z77X-UD5H motherboard, i7 3770 CPU,  Windows 7 64 bit Home/Win 8.1.  SSD drive.  Sonar X3c 64 bit Recordng Software.

     

    Member of Nashville based R.O.P.E.

  • The ATX 12V specification has 2 pins that can be used to turn on the power supply with a paper clip.

    Grounding PS_On with a paper clip turns it on.

    ATX PC Power Supply Pinout and Connectors

    Manually turn on ATX power supply without motherboard

    However I doubt that this is going to fix your issue.  Most likely issue is that the power supply is bad OR the motherboard has Bad Capacitors and essentially looks like a dead short.

    You can use a standard power supply in the Dimension 8400/GX280 Tower System but you need to Hack a hole in the case to get it

    to work.   Newer Dells don't have the issue.

     

    Report Unresolved Customer Service Issues here

    I do not work for Dell. I too am a user.

    The forum is primarily user to user, with Dell employees moderating.

  • This is helpful... I have tried jumpering /PS_ON  to ground, with the power supply disconnected from the system. The fan turns on, and checking output voltages with DMM shows outputs very close to spec. I will check PWR_OK signal again, and make sure it's good.

    Is there a way to get to the power switch, so it can be tested independently? It seems pretty inaccessible.

  • maury11215

    This is helpful... I have tried jumpering /PS_ON  to ground, with the power supply disconnected from the system. The fan turns on, and checking output voltages with DMM shows outputs very close to spec. I will check PWR_OK signal again, and make sure it's good.

    Is there a way to get to the power switch, so it can be tested independently? It seems pretty inaccessible.

     maury11215

    The power switch and circuit board is one unit.

    Dell has not published a guide to remove the front bezel of the Dimension 8400, you can use this GUIDE,

    it's for an Optiplex GX50 Small Mini Tower, the procedures are the same.

    A hint: The Dimension 8400 also, has a Hex headed screw on inside right side of front bezel/panel, just below the front USB ports, holding the front panel to the metal chassis, this MUST be removed and is not mentioned in the guide.

    Bev.

     

    If my answer was helpful, please use the 'Did this answer the question' and click: Yes
    Forum Member since 2001
    I am not employed by Dell

  • Putting a paperclip in the back side of the  PSU connector can FORCE the power supply on.

    However if the Caps are bad they may Blow up and cause a fire.

    There is a ribbon cable from the front panel to the motherboard and then traces from there over to the

    Power supply to turn it on/off.

    You could get a normally open Push button and wire it to the PSON and Ground wire.

    If that works then the switch is broken .

    I have SERIOUS doubts that this is the issue.   I have Many Years Experience with the GX280/8400 and

    never recall that being an issue.   Shorted out USB Ports aka key broken off and Bad Capacitors

    are the issue I remember the most.

    Getting A Used Dimension 8400 is Very Easy for me So it really wouldn't be worth my time to

    Fix a broken Motherboard/Front Panel etc.

    I assume you have an 8400 Tower with the SKYDIVE chassis.

    You can Buy an off the shelf power supply and plug it in and see if it works aka

    the Connectors and wiring are standard.  The only non standard part is the Hole in the rear

    where the power cord goes in .  You basically cut away metal to make a bigger hole in the rear

    and the screw holes are the same as a standard power supply.

    Dell Optiplex GX280 Tower Desktop Computer (DHM) - Refurbished ...

    Micro Center - Dell Optiplex GX280 Desktop Computer Off Lease ...


     

    Report Unresolved Customer Service Issues here

    I do not work for Dell. I too am a user.

    The forum is primarily user to user, with Dell employees moderating.

  • A better solution would be to look for a newer USED dell like an Optiplex GX620 and up.

    Computer Warehouse Tyson's ...

    Micro Center - Dell OptiPlex GX620 Refurbished 555555000149

    OptiPlex GX620 Desktop Product Details | Dell

    The idea is to migrate parts that are not broken to the new system.


    Report Unresolved Customer Service Issues here

    I do not work for Dell. I too am a user.

    The forum is primarily user to user, with Dell employees moderating.

  • 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 ordered a new 400W power supply, installed it, and all is working well.

  • maury11215

    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 ordered a new 400W power supply, installed it, and all is working well.

     maury11215

    Please to hear that replacing the power supply was the solution, to the issue.

    Bev.

     

    If my answer was helpful, please use the 'Did this answer the question' and click: Yes
    Forum Member since 2001
    I am not employed by Dell

  • Testing the power supply without a load can be misleading.  If you unplug the 24 pin connector and jumper pin 14 to ground and the power supply comes on, that is all that means.  If you measure the voltages with no load they can all be OK, BUT when connected and under load the voltages can be bad and that sounds like what happened with this model.

    This is the problem with the $25 Power Supply testers they sell.  It will power on the power supply and it has lights for the various voltages, but that is with no load and can be misleading. 

    I am not a Dell Employee

    Dell forum member since 2002

    Home Built PC with Gigabyte GA-Z77X-UD5H motherboard, i7 3770 CPU,  Windows 7 64 bit Home/Win 8.1.  SSD drive.  Sonar X3c 64 bit Recordng Software.

     

    Member of Nashville based R.O.P.E.

  • I totally Agree with this. Thats why I have a few Sacrificial Hard drives that I use to draw Power when I test a power supply.

     

    Report Unresolved Customer Service Issues here

    I do not work for Dell. I too am a user.

    The forum is primarily user to user, with Dell employees moderating.

  • I was given a Dimension 8400 with the same problem. I put an ATX power supply tester on it,

    and the power supply was okay. I then substituted another power supply, after unplugging

    disk drives and taking out sound and graphics card. It still does not power on. I can see no

    damaged wiring, nor any capacitors with bloat or leaks.

    I swapped the ribbon cable from another Dimension, but still no go.

    I would never buy a Dell (or HP or similar brands) due to the lack of information available.

    Super Angry

  • retspeej

    Is the power button LED, solid green, blinking green, solid amber, blinking amber, or off?

    Check the sequence of the diagnostic lights on the back panel of the case, see HERE.

    Are there any 'Beeps'?

    Bev.

     

    If my answer was helpful, please use the 'Did this answer the question' and click: Yes
    Forum Member since 2001
    I am not employed by Dell