Question Dell Optiplex 780

[loceur]

So recently just for fun I decided to pick up a Dell Optiplex 780 DT with an Intel E5800, and decided to throw in an RX 580 and just basically scrap together a riser card, an external EVGA 500 W PSU, and basically boot it up.
The problem arises when a driver is installed and the screen begins to lose signal so I suspect that the GPU is not getting enough power from the PCIE slot.
I've tested every single component and they all work fine with a different motherboard, however when using an EVGA PSU connected to the Optiplex Mobo with a 24pin to mini 24 pin adapter, the PCIE seems like it's not powering the GPU enough or shuts it off. Sometimes it also flashes green and yellow, and drivers have been reinstalled and uninstalled using DDU. The PSU is working in another system, and so is the riser card and the GPU. Any suggestions?

 

[Zakster]

If available try another GPU. If the problem still occurs its a power delivery problem.
If Not available try and test the GPU in another system and test if the problem occurs.

This should tell you if it's the GPU or Power delivery which is causing the issue.

 

[loceur]

Yeah so with another board the Rx 580 works with no hitches, and I think it is a power delivery problem, I have yet to try another GPU on the optiplex however, the pcie express on the dell board is supposed to deliver 75 watts and the PSU should be delivering the rest, so I'm not sure whats causing the problem. The GPU is completely functional and the PSU works with no problem on another board too. Any suggestions to fix either the mobo power delivery or to circumvent the PCIE failing to deliver full power and just let the PSU handle the wattage. Thanks for the reply!

 

[Zakster]

Do you have the GPU connected directly to the PSU ir just MB power?

 

[loceur]

I have both a[n] 6+2 (8) pin connected to the GPU and a riser card connected to the MB. The riser card and the GPU functions on another board just fine and can run benchmarks, but on the Dell it won't go past the windows boot screen or sometimes it does work then freezes up and loses signal or flashes green or yellow. I can't test the dell mb without a riser card however due to the proprietary form factor, and the heatsink is in the way of the GPU size. I was thinking it could have to do with the 12v of the PSU and the mini adapter to the mobo could be tripping the motherboards pcie slot. Any suggestions would certainly help

 

[william p]

Dell BIOS from the BTX series computers have a known issue with AMD video cards after about the HD series.
Anything form R9 3xx and up won't work. (R9 285 also). Those GCN version can't display the Dell VESA mode 103 video resolution.
Sometimes they lock up, some times you can press f1 and boot, but the BIOS will never be seen again.
BTX started back in the Pentium4 era. It didn't get all the updates ATX did. NVIDIA cards all work just fine.