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I try to replace GT 840 dPGU with eGPU on V3-572PG mainboard for which I have circuit and boardview.
I'd desoldered dGPU. Then after study of boardview I could easy match pins from dGPU socket to pins of EXP GDC 1x mini-pci riser cable (I'll build my own 4x riser later). Then I soldered them. These below are already connected:

value           riser's pcie slot                           exp gdc cable second end (mini pcie interface)          dGPU pin (from boardview)
tx0+            14a                                         23                                                      479
tx0-            15a                                         25                                                      453
rx0+            16b                                         33                                                      581
rx0-            17b                                         31                                                      582
vga_clk+        13b                                         13                                                      531
vga_clk-        14b                                         11                                                      504
gnd             4a, 7a, 13a, 16a, 18a, 4b, 12b, 15b, 18b    4, 7, 9, 15, 18, 21, 26, 27, 29, 34, 35, 40, 50         180
+3,3            <Does not go onto riser's pcie socket>      +3,3                                                    161

Also pin peg_clkreq# on dGPU socket is connected to gnd.

One wire is left not connected which is pci-e pin 11b:

value   
pwrgd           11b                                         22 (PERST)

Where I should connect it?
pltrst_vga# or gpu_pex_rst_hold# or sys_pex_rst_mon# or maybe some combination of those?
It looks like it can't work without it.

Can someone look at schematic available here:
link to schematic
and answer?

And last question. If this is anyway possible then do I also need modded BIOS or something?

brhans
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Daro
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    strange project! I always think of computer laptops and motherboards as non-serviceable. anyway this signal says the power is steady and the GPU can start working. It might exist somewhere else on the motherboard, maybe near the power supply section. – user253751 Feb 07 '23 at 09:31
  • well it's a little old mainboard - at least 5 years old. What I want to achive is just get pcie x4 link with external gpu. If pcie 1x riser works in such config then most propably all 4 lanes can be connacted too. There is no any other way for x4 link. LAN is x1 and mini-pcie is x1. – Daro Feb 07 '23 at 09:38
  • If I'm thinking incorrectly then correct me please. The PWRGD (power good) signal is generated by the pci device only when pci guest <--> host negotiation completes succesfully and then stays 1 (higher voltage) and for example makes mini-pci PERST# signal go from 1 (lower voltage) to 0 (higher voltage), so TX, RX, and CLK signals are ok. Can I check with multimeter what voltage gets stayed on that pin (PWRGD) ?. There is PEG 2.0 x4 in my mainboard and EXP GDC (1x) on another side of cable. What possible voltages should I expect in both cases (when negotiation success or when it fails) ? – Daro Feb 07 '23 at 10:52
  • Very ambitious project! Might be simpler to try with a simpler card like a LAN card to get the link up. Do you have access to a PCIe-frequency scope? – pjc50 Feb 07 '23 at 11:04
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    @Daro Google tells me PWRGD comes from the power supply. It indicates the power is good, it has nothing to do with the negotiation. I expect that most cards remain "in reset" (in electronics terminology) until PWRGD is active. – user253751 Feb 07 '23 at 11:09
  • @pjc50 I'm not yet skilled so much. What do You mean PCIe-frequency scope ?. An oscilloscope that can catch signals at such freq. or what ?. Now I don't know. Just unexperienced was thinking that PWRGD signal is DC at constant voltage – Daro Feb 07 '23 at 11:11
  • Normally to debug a PCIe link you'd need to see if the signal is clear: https://electronics.stackexchange.com/questions/180012/pcie-diagnosing-and-improving-an-eye-diagram ; if it's just a bunch of loose soldered wires and not controlled impedance and equal length traces, the signal will deteriorate and may not work. – pjc50 Feb 07 '23 at 11:14
  • ok. So how I soldered wires is one thing but another is the question does that that missing signal connection (PWRGD) as for this moment break overall functionality ? – Daro Feb 07 '23 at 11:21
  • I'm sure I'm not best of soldering, but if You want to look then here You go – Daro Feb 07 '23 at 11:31
  • [link](https://drive.google.com/file/d/1HMGz_GmEOl3-M84YtZh546fkiXYp5l_7/view?usp=sharing) – Daro Feb 07 '23 at 11:31
  • there are no short circuits – Daro Feb 07 '23 at 11:32
  • @pjc50 Can it pass ?. What do You think ?. I won't solder again. That is My maximum skill at the moment. – Daro Feb 07 '23 at 11:46
  • @Daro you need to keep the PCIe signal pair wires together. They need to be length matched as closely as you are able, and you need to keep that shielding over each pair as much as possible. I can't tell what cable you've used there, but a cut open USB-3 cable is more likely to work than anything else you might have lying about. – brhans Feb 07 '23 at 12:45
  • @brhans Upps I didn't know that. Thanks for letting me know. That micro-soldering is still hard for me. Maybe later I'll try to make things better – Daro Feb 07 '23 at 13:02
  • I can't see the schematic but I would make a guess that connecting PWRGD# to PLTRST_VGA# is not unlikely to work. Wouldn't say it *will* work, either. PWRGD# is not a difficult signal, it just tells the card to stay turned off while the power supply is booting. Based on the name I would say that PLTRST_VGA# probably tells the dGPU or maybe the monitor to stay turned off so it might be a good enough match. – user253751 Feb 07 '23 at 16:14
  • @user253751 can't download schematic ? It's packed with 7-zip. Maybe You can see [this picture](https://drive.google.com/file/d/1U-mTA2WZgMngWCq5fV-i_4ZCGluGiChm/view?usp=sharing). Please comment – Daro Feb 08 '23 at 08:26
  • @Daro based on the naming I would consider whether PWRGD# is equivalent to VGA_PWROK. however, the # in PWRGD# indicates that it's inverted (low when power is good) whereas VGA_PWROK is probably high when power is good (you would have to trace it in the schematic and double-check that). There might already be an inverted version somewhere, or you might need to add an inverter. – user253751 Feb 09 '23 at 08:35
  • @user253751 at first I need to improve My soldering - at least for tx, rx and clk wire pairs. brhans gave Me right suggestion how to do that. I think I need to build some tripod which will hold wires for Me in place in proper position so I'd be able to solder them easier. – Daro Feb 09 '23 at 10:13

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