Monitors not waking from sleep with Nvidia GTX660 GPU

[Anssi]

I had to replace the GPU to my 4,1->5,1 Mac Pro, and got a GTX660 (unflashed) for a good price. I downloaded the current drivers, and everything works fine. Except that when I wake the Mac up, monitors stay black. I have to do hard reboot to get them work again.



This doesn’t happen when I manually put it to sleep, and turn on immediately. Only when it’s been sleeping for a longer time.



What causes this, and is there something I could do to prevent it? Or is it normal behavior with unflashed GPUs?



Currently I have both computer sleep and display sleep turned on in energy saving options. Does it make a difference if I turn them off, and just use manual sleep command?

 

[Anssi]

Apparently nobody here has had the same problem of monitors not getting signal after sleep?



I heard about one similar case, but unfortunately he did not remember anymore what he did to fix it.



- The monitors are Dell U2413, both DVI and DisplayPort connections behave similarly.

- I tried removing the original ATI Radeon HD 5870 GPU, but it did have no effect, so I put it back (to be used if I need splash screen)

- OSX is El Capitan

- And apparently the problem does not need long sleep, although I first thought so. It happens also if I manually put it to sleep and just wait a bit.



I would not like to upgrade OSX in this point in order to enable use of older applications. But that can be done if needed.