Dell Optiplex 790 Front Panel Pinout

[cdominic3]

Anyone know how the front panel pinout of the Dell Optiplex 790 is laid out?

 

I'm building a custom $150 PC, and I've stumbled upon a Dell Optiplex 790, didn't realize that the front panel connectors were proprietary. I don't really need the full layout, just which ones the Power Switch +/- pins fits into.

 

I've seen this (http://pinoutguide.com/Motherboard/dell_optiplex_front_pinout.shtml), it's the same one, but it only has one Power Switch labeled on here - doesn't even specify the +/-.

[Evanair]

Take a screw driver and short random pins together. You can't do any damage (long as you don't stab or break anything)

 

Once it turns on, you found the correct two.  It's just a jumper switch, nothing special. Use to do this all the time to boot systems out of a case.

 

Also, they aren't pos/neg. It's a jumper not an light

[oskarha]

Power switch doesnt have +/-

[cdominic3]

@oskarha well, alrighty then.

[cdominic3]

@Evanair @oskarha figured it out guys. power switch pins weren't a part of the 34-pin front panel header. they were on a different 5-pin header.

 

what i then did was take the power switch cable from the dell optiplex case, which included the whole power button, took out the button and front panel header for the power switch/led, and put in the dell power button and connected the headers to the corresponding pins. works like a charm now.

 

thanks for the help! wouldn't have figured this out without the two of you! 

[Cracklingice]

Sorry about the slight necro but I bring to anyone in the google or forum search the pinout for the 34 pin connector on Dell Optiplex 790 Desktop PC.  I am not certain what else shares the exact same pinout.  The LEDs use a common positive and the individual LED labels are the negatives.  They are 5V LEDs.  Anyway, onto the pin out pic.

 

Edited January 19, 2017 by Cracklingice
LED explanation

[madtrigger]

On 9.12.2016 at 10:47 AM, cdominic3 said:

@Evanair @oskarha figured it out guys. power switch pins weren't a part of the 34-pin front panel header. they were on a different 5-pin header.

 

what i then did was take the power switch cable from the dell optiplex case, which included the whole power button, took out the button and front panel header for the power switch/led, and put in the dell power button and connected the headers to the corresponding pins. works like a charm now.

 

thanks for the help! wouldn't have figured this out without the two of you! 

Can you please tell me which 2 of the 5 pins have to be used in a regular PC case, where there is only a 2 pin power switch? Thanks and kind regards!

[madtrigger]

On 18.1.2017 at 8:23 AM, Cracklingice said:

Sorry about the slight necro but I bring to anyone in the google or forum search the pinout for the 34 pin connector on Dell Optiplex 790 Desktop PC.  I am not certain what else shares the exact same pinout.  The LEDs use a common positive and the individual LED labels are the negatives.  They are 5V LEDs.  Anyway, onto the pin out pic.

 

If I build this board into a regular PC setup, is there even any need for this 34 pin connector? Also, as cdominic already said: the power switch is on a 5-pin connection, so even usb etc. should be accessible from the rear inputs. Right?

[Cracklingice]

On 8/7/2017 at 0:48 PM, madtrigger said:

Can you please tell me which 2 of the 5 pins have to be used in a regular PC case, where there is only a 2 pin power switch? Thanks and kind regards!

When I did mine, I had to actually put the case switch in parallel with the original Dell switch or it wouldn't work.

 

On 8/7/2017 at 0:51 PM, madtrigger said:

If I build this board into a regular PC setup, is there even any need for this 34 pin connector? Also, as cdominic already said: the power switch is on a 5-pin connection, so even usb etc. should be accessible from the rear inputs. Right?

If you do not have the 34 pin connector plugged in, you will get an error on boot.  It may be something you can just hit a key to get past it, but it will still happen.  It may be possible to just bridge the grounding pins to fool the motherboard into thinking the front panel is connected, but I haven't looked into it yet since I have the actual front panel connector.

[asand1]

Just buy the switch and mod it in? It is a pretty cool wsitch with its built in LEDs.

http://www.ebay.com/itm/Dell-Optiplex-790-990-SFF-PC-Power-Button-Switch-Cable-VW42T-0VW42T-Small-Factor-/322603337416?epid=1600707213&hash=item4b1ca846c8:g:dDsAAOSwdIFXyhDv

[madtrigger]

13 hours ago, Cracklingice said:

When I did mine, I had to actually put the case switch in parallel with the original Dell switch or it wouldn't work.

 

If you do not have the 34 pin connector plugged in, you will get an error on boot.  It may be something you can just hit a key to get past it, but it will still happen.  It may be possible to just bridge the grounding pins to fool the motherboard into thinking the front panel is connected, but I haven't looked into it yet since I have the actual front panel connector.

Thanks for your reply. I don't have the 34 pin connector since I want to use this board in a regular case / setup. Your excessive use of "may"s are really subjunctive – seems I will have to test it.

But I really like your idea of just bridging the grounding pins. But how exactly would you do that? Would I have to connect GRND1 + GROUND3 and GRND2+ GRND4? I am in no way familiar with electronics.

[Cracklingice]

On 8/8/2017 at 2:48 PM, asand1 said:

Just buy the switch and mod it in? It is a pretty cool wsitch with its built in LEDs.

http://www.ebay.com/itm/Dell-Optiplex-790-990-SFF-PC-Power-Button-Switch-Cable-VW42T-0VW42T-Small-Factor-/322603337416?epid=1600707213&hash=item4b1ca846c8:g:dDsAAOSwdIFXyhDv

 

22 hours ago, madtrigger said:

Thanks for your reply. I don't have the 34 pin connector since I want to use this board in a regular case / setup. Your excessive use of "may"s are really subjunctive – seems I will have to test it.

But I really like your idea of just bridging the grounding pins. But how exactly would you do that? Would I have to connect GRND1 + GROUND3 and GRND2+ GRND4? I am in no way familiar with electronics.

 

I get my new power supply in roughly 48 hours and I will be able to put the one in my new rig back into my modded 790 rig.  I will perform some testing tomorrow for tricking the board into thinking the 34 pin is connected even if it isn't and I will try to get a picture of how my power switch is set up and what wires I had to tap into.  If I did not have the original power switch hooked up, the computer would turn on by itself when plugged in and pressing the switch did nothing.  There is some voodoo going on with that switch that I cannot understand.

 

And yes I used a lot of mays because I had the 34 pin so I have it connected and zip tied to the side of the bays in the case.  I even wired up my front panel audio ports.  Although honestly I should have just plugged the headset into the back of the computer.  Better sound quality there anyway.

[madtrigger]

Okay, so my Mainboard arrived today and I started setting up my system.

 

I only attached the PWR switch of the case which works nicely. Unfortunately, I had to break the plastic surrounding of the 5-pin socket ... but ... oh well, who cares. When the system receives voltage for the first time, it powers up automatically, which is weird but no problem since it only happens once.

 

The system can be started without having the 34-pin frontpanel being installed!

 

A general nuisance is the alert of missing dell components. You can skip them by simply pressing F1 but they will be shown every time I boot the system. The board complains about missing CPU fan cable, missing HDD fan cable, missing frontpanel and missing (5-pin) power cable,  ... so basically it complains about everything that was proprietary and is now missing. 

 

I installed the stock CPU cooler and it gets its power via Molex to Fan adapter. It runs perfectly well – albeit at full speed.

 

The biggest problem I now face is the installation of the graphics card. The 24 pin power connection is in the way of the cooler of my 2-slot graphics card. I now have to either buy a 1-slot card or a very short 2-slot card. Another idea I had was simply buying a PCIe adapter and place the card beneath the mainboard. What do you think about this problem? Which might be the best solution?  Edit: I just ordered a PCIe riser which will hopefully solve my problem. 

[Cracklingice]

What motherboard did you get that causes issue with the graphics card?  Mine only had issue with the sata ports (and I got a right and a left angle sata cable to at least have two available).
Here's an album with the pics from todays rebuild. 

 

 

And here is a pic of how I wired up the dell switch in parallel with the case switch so that the switch actually worked. (click for full size)

 

As far as the front panel connector, I forgot to check to see what happens if I just connect the grounding and or common pins together.  It may just check for that or it may be checking for the diagnostic lights that are part of the front panel.  Ultimately I just ordered all the little bits from ebay.  While it was an interesting challenge to get the dell mobo working in my case without errors and with the front audio jacks, I do still regret not just selling the Dell mobo on ebay and getting a normal mobo for the cpu.  It ended up costing just as much to get the Dell heatsink, case fan, front panel connector, switch and temp sensor (though I bought only one of the two not realizing there was two and it has never complained about the missing one).