Quote from: Watjila on September 13, 2016, 07:59:27 AM

Quote from: sp_ on September 13, 2016, 05:34:23 AM

Quote from: reb0rn21 on September 13, 2016, 12:50:43 AM

I must agree too Z170 chipset is having problem with 3+ cards on most boards, its prolly bios related, but who ever is doing testing first disable all non needed IO and internal devices as:
- sound
- ports
- any add in hw as firewire, wifi, etc
- set PCI-e to x1 mode if possible

And only then test it, also better use win10 because it should handle 8 GPU with no moded drivers

With this board you need powered risers. The asrock btc boards have 2x 4pin molexes in the board to give extra power.

I like the Asrock motherboard with the 2x 4pin molexes in the board to give extra power. that is much safer.

You actually need zero molex on the mainboard when you have all the cards on molex powered risers (the BIOS will probably demand it anyway and there is no harm in obeying).
It shouldn't be a problem to run 2 cards sitting directly in 16x slots either (if the PSU has decent quality ATX 24-pin wiring/termination and the motherboard was designed for 2+ graphics cards).

On the other hand, I managed to burn two molex/sata cables and a modular socket on a Be Quiet! PSU while running six RX 480 cards on molex powered risers.
Since the PSU had 5 sockets for sata/molex cables (it was actually 6 but I failed to realize that there is an extra, different looking socket, intended for a short molex cable which is there for motherboards with an extra molex but could be used as any standard molex...) and I had 6 cards, I decided to connect 2 cards per cables (6 risers to 3 cables in total).
At first, one of the modular sockets melted a bit with the cable connector getting badly burned in it. (It was still running but I noticed the smell, so turned it off and started investigating.)
Since the other 2 cables looked perfectly fine I thought it was a random fault (either I failed to push it into the socket properly, or the connector was faulty to begin with, etc). I was down to 4 functional sockets in total anyway (well, actually 5, though I believed it's only 4 but it was less than 6 now anyhow), I didn't really have a better choice but to pick another cable and continue to run with 2 risers per cables.
The next time I noticed some smell again, turned it off, and saw as another sata/molex cable (with 2 risers on it) started to burn out. This time, the socket on the PSU remained intact but the cable started to loose it's coating and the SATA plug itself was really hot.

So, these modular sata/molex sockets/cables are clearly not ready to handle this kind of load (2x75W or whatever these cards might eat from the PCI-E slot).
The PCI-E, CPU and most of the ATX 24-pin wires seem to be significantly thicker than these sata/molex wires. The former group of wires go from point-to-point, directly terminated at both ends while the latter ones are "chained" in a way which is (in hindsight) clearly not ready to handle this kind of load (it's basically a single long cable and all the SATA/molex plugs are simply pressed on them, cutting through the insulation and keeping the metallic contact thorough "pressured razor blade" kind of fashion).
It's also notable that the extra short molex, intended for direct motherboard connection, is also point-to-point, directly terminated at both ends (not a razor blade pressured and chain-able kind like all the rest).

The TL;DR lesson is that even though the ATX 24-pin connector/cable clearly has it's own limits, the sata/molex cables intended for hard/optical drives can be significantly weaker.

I recently replaced that PSU and wired the new one with 1 card per molex/sata cable from the beginning (it has 6 identical sockets for these kind of cables). I will probably use the slightly damaged PSU with 3 or 4 cards at max later on (when I will have some fresh mining profit to reinvest).