Optiplex 790 MT Upgrading Question

790 is non class 2.3.1 UEFI system that will boot and run XP. Neither the power supply nor the video card will EVER work in this system. R series Radeon cards REQUIRE WIN8 or WIN10 UEFI bios with secure boot off and CSM ON.

Recommended power supply upgrade that defiintely works is EVGA 700BR or 700B1

N1 W1 B2 BQ etc versions from SAME VENDOR Do not work.

https://www.bestbuy.com/site/evga-700w-atx12v-eps12v-80-plus-bronze-power-supply-dc-dc-technology-black/6346160.p?skuId=6346160

Note 150W on 3.3v / 5v rails combined

R series Radeon cards require UEFI bios that 790 does not have and will never have.

RTX series Geforce cards are in the same category of not working.

Older Pascal based GTX 1030 1060 1080 cards work fine as long as they are short versions so that they physically fit into the case.

I would really like to thank @speedstep for all his knowledgeable replies concerning the 790 here in the forum. They're spot on and allowed me to really upgrade my MT with success.

I just wanted to share some of my personal insights:
- the Antec HCG750 Bronze PSU also works (but requires you remove the entire cover spring mechanism to fit - and then the cover doesn't close anymore);
- long cards don't work inside an MT case (such as my GTX 1080) not only because of the HDD metal frame but also because the SATA ports are in line with the 16x PCIe slot - 90degree SATA adapters won't work. You'll need a PCI riser/adapter (no loss in performance), but then there really isn't a place to vertically mount your monster graphics card inside the case.
- (observation) the mobo only has 1 fan header, and it's a 5-pin. You can do what this guy did https://linustechtips.com/main/topic/810007-dell-optiplex-790-build/?do=findComment&comment=10378974 or split the wires of the back fan to power an extra fan.

Cheers!

sorry I posted smbios version for uefi class v.

my 790 with newest BIOS

boots to UEFI safeboot,  100% perfectly w10-64bit V1909 (installs zero issues at all)

and with GTX1650 new,  Zotac. (new as new can get in fact !) from newegg, never from fleabay .

I can not try all 12 makers or RTX cards. new.  sorry never happen,

we all know some cards fail,  but there is  sea of cards, and some fail for GOP reasons

not compatible with DELLS GOP CODE. ( finger pointing will never end i bet)

why not ask Gigabyte 4GB RX 570,  them about this on THEIR Form, ask for legacy mode?

if using that mode, or safeboot you never said what mode. used. my 790 does run UEFI perfectly secure boot.

the maker of that card does offer variant , VBIOS. TALK TO THEM first.???

if you read on their forum you will see posts there of some OEM PCs failing. Just like you.

speed step , broad brush effects. and his endless CUT/ PASTED posts.?

many of your facts are wrong.

ever actually try, or even use the newest BIOS ON THIS EXACT PC< I HAVE>

and there were zero problems. at all.

but I do not have  Gigabyte 4GB RX 570, to test.. (and has newer version 2 card, is your card V2?)

I have R9-380 that works but too cheap to go RX me. ...... have you tried?

GTX1650 does work, for a fact, newest BIOS. any mode you can name, any test.

my 790 does act like 2.3.1 UEFI, per the spec, UEFI, states. (dell has no list to find, at all on this , current !)

but what is in that newest BIOS DELL IS NOT SAYING AT ALL .

try F81  VBIOS for card at gigabyte..?

you can also at any time turn off PCI-e GPU from auto to HD and then boot and set bios

then switch back to RX570 and boot windows.(lots of top shops do this , as SOP)

or reset BIOS,  (looking first what settings you have now) see on F2 page one bottom load defaults.

turn off PXE nic and nic boot, make sure HDD/SDD0 is first in boot order. (or as you want)

of you look here under gigabyte see lots of cures, on topic,

UEFI cards do not work with class 0 and class 1 Bios.

Specifically they do not support F2 DOS VESA video mode 103.

https://www.wimsbios.com/forum/video-vga-and-other-bios-firmware-f28/video-mode-103-not-supported-this-gpu-sapphire-285-itx-t14364.html

This is a problem when you want to change something in bios.

Nvidia cards up to pascal aka GTX 10XX series work fine in older bios dells.

Newer RTX cards do not work correctly due to also not supporting MSDOS VESA video mode 103 for F2 cmos setup.

The 1080TI card in the video is used on an XPS 400 from 2006 with Pentium D processor.

https://www.youtube.com/watch?v=qa9b0TkTsLM

Secure Boot requires a PC that meets the UEFI Specifications Version 2.3.1, Errata C or higher.

this is what is published,

and the BIOS in mine reports, the 2.6 version, so does DELL  BIOS LIE? ,

ok I will test mine to see if w10-64bit runs on new SSD in full UEFI mode.  790MT fresh new ver. BIOS.

the 790 is circa 2011, so may be DOA for UEFI,  so I will test that. or DOA for GOP, (fun to say at same time)

w8 is October 26, 2012,  just 1 year after 790  first sold, Did, Dell leave 790 out to dry for w8 up.? hummm

got w10 64bit to install onto my 790mt in UEFI mode. with no GPU card just the iGPU HD. by intel.

no problems , i installed a GTX1050 card, new it is and it work out OOBE, out of the box, PnP works..

The UEFI 2.6 does not care if I swap GPU cards like a mad man.   (a surprise to me must be a class3 only thing)

I will test more cards this week,  790mt +w10-64, UEFI loaded, fresh, now. I did the 4 tests at Tenforms and all shows UEFI fully active. and SSD boot drive is GPT formatted. automatically I might add.. (from erased SSD)

so far no problems with F2 or F12 bios screens,  I will keep testing this, setup.

FYI (UEFI tid bits)

here are the wiki reported rules. #2 is clearly 790.. and not class 0 or 1.. (zero means pure BIOS)

UEFI class 0-3 and CSM

PCs are categorized as UEFI class 0, 1, 2, or 3. A class 0 machine is a legacy system with a legacy BIOS; i.e. not a UEFI system at all.

A class 1 machine is a UEFI system that runs exclusively in Compatibility Support Module (CSM) mode. CSM is a specification for how UEFI firmware can emulate a legacy BIOS. UEFI firmware in CSM mode loads legacy bootloaders. A class 1 UEFI system may not advertise UEFI support at all, since it isn't exposed to the bootloader. It's only UEFI "within" the BIOS.

A class 2 machine is a UEFI system that can launch UEFI applications but also includes the option to run in CSM mode. The majority of modern PCs are UEFI class 2 machines. Sometimes the choice to run UEFI applications vs. CSM is a one-or-the-other setting in the BIOS configuration, and other times the BIOS will decide which to use after selecting the boot device and checking whether it has a legacy bootloader or a UEFI application.

A class 3 machine is a UEFI system that does not support CSM. UEFI class 3 machines only run UEFI applications and do not implement CSM for backwards compatibility with legacy bootloaders.

There is no such thing as class 2.6 uefi so I have no idea what you are talking about.

https://docs.microsoft.com/en-us/windows-hardware/design/device-experiences/oem-uefi

Class 2.3.1  Windows 8 Bios came out in 2012.

790 does not have WIN8 bios key with SLP 3.0.

The reason you need MSDOS VESA video mode 103 is so that F2 cmos setup works with your video.

This is not needed for UEFI bios machines.   This is also why Older Nvidia and ATI cards work fine but newer RTX and RX series cards do not.

In order to support UEFI POST and boot, you must provide the following.

sorry step it does work on my 790, ever own one? and test GPU on one MT>.?

gtx1650 works(turing class and brand new for sure) (I can not test all 100 RTX cards sold, no $10,000 here just for fun, testing.

and you added now the magic word Newer,

ok.  

sure we all know that newer cards even super new MAY BE 100% UEFI only cards CLASS-III,  some will be are sold now.? I don't know.. but.....

But if you read every web site for every card made they do not even mention UEFI at all, they all tell  you that GOP solves that ! when asked,  and I guess SOME dells fail for GOP support,  so is  a DELL problem.. that..

when found.

so the answer is buy only Dell GPU cards that are not sold now.. wow.

MY 790MT is UEFI class 2.6 (seen in msinfo32.exe ) clear as day, newest BIOS what else.

why say this for any 790

"UEFI cards do not work with class 0 and class 1 Bios." (but is obvious)

and is off topic too.  2.6 here.

but also because the SATA ports are in line with the 16x PCIe slot - 90degree SATA adapters won't work.

you bought the wrong 90degree sata cables some do work, and is best...

riser board invite huge limits on DC power,  making GPU cards BSOD. (but gee vast riser sold , no spec on any)

the silver heat sink on my 790mt south bridge is higher than my sata 90deg, cable top, so do not hit.

the cable goes to the right, facing rear of mobo.

no problems here, (yes the PSU clamp is there and is not needed)

the real problem , endless is Dells that do not support GOP, (AMD has preached this issue for  a very long time)

new and proper GOP = Graphics Output Protocol

also some top makers of GPU card like mighty Gigabyte even has special Vbios for lame BIOS PCs.  sadly .

there is no class 0 or 1 here.

why post off topic this, its a 790mt,

why post facts on PCs that are off topic.

not THIS PC...

there is no w8 here (nor is it sold..) forget w8 will you:?

there is no old BIOS here, it is NEW, read the SUPPORT PAGE first then get the newest BIOS and learn that the PC runs in full UEFI secure boot GPT, and those structures, end to end, learn that and stop pasting myths... please.

IT  run, great, and tested by me on over 20 GPU cards,  all even swapped in UEFI mode securebooted, no problems. zero issues, here. Why the OP fails only careful testing can learn why,

even hot swapping cards will cause black screen ever do 100s of cards and mess up one time, bingo latches up.

sure some rare cards fail sure. but is not ALL CARDS ,not ever all. (ON THIS PC)

"

there is no class 0 or 1 here.

why post off topic this, its a 790mt,

why post facts on PCs that are off topic.

790 MT is Class 0 or 1 LEGACY bios and it will run XP.

So again I have no Idea what you are saying.

390 790 990 DO NOT HAVE CLASS 2 bios.

XP and legacy MBR are NOT Compatible with GPT/UEFI bios.

Class 1: UEFI Firmware which emulates as BIOS only. No UEFI support is provided. This was used by Platform Manufacturers to transition to UEFI standard while essentially maintain a BIOS platform, as most OS from 2009 up to 2012 were not UEFI aware. Class 2: These Platforms support both UEFI and Legacy BIOS via CSM.

Class 3 bios removes all legacy and CSM.

UEFI machines can have one of the following "classes", which were used to help ease the transition to UEFI.

• Class 0:Legacy BIOS
• Class 1:Legacy BIOS with UEFI code, although it does not support UEFI booting
• Class 2:UEFI with CSM  added for WIN8 in 2012
• Class 3:UEFI without CSM

OP not sure what PSU that is? got a link?, links show full spec, so we can see it read it and comment.

Gigabyte 4GB RX 570,got a link to this card? its not just one card but IS 1 of 12 makers. sure..

have you fully discharge all CAPS in the PC, and re-seated the card? so it is not latched up ? hard reset this.?

pull line cord push power button until all fans stop twitching and all LED do not glow.

then put the card in the blue x16slot. (towards center of mobo.)

then power on the PC see if BIOS works... if not reset BIOS, next (some pull the , new coin cell out)

if your old RTC coin cell is same as PC it is no good.

BIOS OPROM enabled.?

this card has variant (derivatives ) with different NEEDS. for power. this card needs 150watts all alone.

about 75 watts from aux and 75watts from PCI-express power pins.

got this card?, got  that 8 pin AUX, are all 8 pins wired to PSU>?>????

the benchmarks show lots of support , for your PC and matching card,  see answers by.TechGee on our form.

see gpu caused black screens 

best PSU to use  (there are vast) is TX-M750 corsair,  25amps low voltage and 63amps 12vdc single rail.. buy that. and not need to upgrade for a decade?

hey good luck !!

Hello @savvy2 

I also have a Dell Optiplex 790 MT. I am having my hopes up that you mentioned using GTX 1650 on this machine. I had the machine originally with XP OS that has a Win 7 Pro license and upgraded with Win 10 x64 OS. That being said, I wanted to confirm if the GPU you mentioned is similar to this "PNY GeForce GTX 1650 4GB Single Fan Graphics Card VCG16504SFPPB-O"

If yes, automatically 790MT needs an upgraded PSU. I am not sure if it was mentioned on this thread that this PSU is compatible with "evga 700 b1" 

Then again, as an alternative to this, is "Thermaltake PS-LTP-0650NPCNUK-2 Litepower/650W/Non Modular/ATX 2.3 & EPS/A-PFC/12cm/EU/Non 80PLUS Black" OK?

BTW, I am no expert but i was hoping anyone could let me know as GTX1650 is a promising low powered GPU.

Thanks