GTX 780ti repair attempt

[dicky96]

Hi guys
First let me just mention I have been posting about this on badcaps forum over the last couple of days, so apologies to anyone who also reads that forum.  For anyone else all the details of what I have found so far are on this thread

https://www.badcaps.net/forum/showthread.php?t=83970

Seeing as we are on week six of lockdown in Spain, with the strictest restrictions in europe - I decided to try and learn to repair GPUs as it is something I want to do but have no experience.  And now I have plenty of time on my hands. Soooooo....

I have two GTX 780ti and one GTX 780 (that was supposed to be a 780ti but isn't) which I got off ebay spares or repair, and also a GTX 770 that I got some time ago at the local flea market for 2 euros.

Of these four, I have a Palit 780ti and a Gainward Phantom 780 which look to be pretty much the same PCB, and a Gigabyte 780ti that is a different board design and looks rather similar to the GTX 770

One of the guys on badcaps pointed me to a thread on here
https://www.eevblog.com/forum/repair/nvidia-gtx-780-pcb-circuit-component-id/
and it seems there are folks here who know about these cards so I thought i would ask here 

Basically I have
Gigabyte 780ti - shorts on both Vcore and Vram
Gigabyte 770 - no shorts on Vcore or Vram but after powering on a few times one of the FETs sparked and a little bit of plastic blew off it!  It also has 3 capacitors missing on the 12V supply.
Palit GTX 780ti - short on Vram supply.  I already removed the inductors to trace the fault and found one dual FET driving Vram was short to 12V
Gainward Phantom - no shorts on Vcore or Vram but I have no output from either Vcore or Vram VRMs

All the details are on badcaps, but basically I traced the lack of Vcore and Vram on the Phantom to the fact the PWM controller is not enabled.  I then found I have a missing supply rail which, from the other thread posted here, I found that rail is PCI-e supply.  Someone else has been 'messing' here so I had to clean up their rather untidy soldering.   I found the controller RT8071 has 5V input, and no short on the output but the EN signal is low so it can't start.  But where does the EN signal come from?

That's as far as I have got with these - over to someone with more experience than me, which isn't difficult as my experience of GPU repair is like zero.

See attached pics, they will explain this much clearer.

cheers