Do you think these spikes can be the reason why my rig freezes? I will describe my problem a little.

I have a 7970, a 280x and two fury nitros. During the last couple of weeks I have been trying to run my system stable with no luck. Freezes can happen at any time after starting to mine. Sometimes minutes, sometimes hours.

Rig specs: Asrock 970 extreme4. Sempron 145. 8GB ram. EVGA 1300 G2. Sapphire 7970 ghz edition, sapphire 280x vapor-x, 3x sapphire fury nitro OC. Tahiti cards undervolted on bios, fiji cards on msi afterburner. No OC on furys. Win 10. 12.6.3. CM 11.1.

First I changed all risers to v6 ones.

Next I upgraded the processor to athlon x2 because I noticed that I was getting less hashes when MSI afterburner was on and I thought the system would be more stable.

After a couple of days more I changed the mobo to asrock h81 pro btc with celeron 1840.

Still no luck.

I thought that the power was insufficient so I added a corsair rx1000 linked with an add2psu device.

No luck, freezes persist.

Changed EVGA to corsair hx1200i. This psu is powering mobo, raisers and tahiti cards.

Nothing changed.

I stopped undervolting. Still same freezes.

One fury died the day before yesterday. No fans, not detected in win 10, not detected on ubuntu, mobo not booting when the card is alone.

I changed risers again to the furys.

I used separate cables for each riser.

I powered the offending fury card with one cable for each connector. Still the same.

I tried catalyst 15.12. Same effect.

Sometimes I see 511 degrees in the fury card on CM log prior to freeze, sometimes it just stops hashing without any error and the watchdog doesn't restart the miner, sometimes all 4 cards go to 0.000 hashing without any error, sometimes after gpu reported incorrect temperature 511°C.

I'm already out of ideas.

Any hint, anyone?

Edit: typo