I have a S9 that is a few months old.  It has been working great, but recently the hashrate keeps dropping to zero.  It's acting like it's overheating and the safety shutoff is kicking in, but I know the shutoff won't kick in until the board temp reaches 80.  The chip temps have been getting into the 80's some since it's been warmer, but as I've researched I see lots of people running with chip temps in the 80's and sometimes higher.  The last time the hashing dropped all of the chip temps were at 76, so I would imagine the board temp could not be 80. 

I also have 2 L3+ running right next to it and they are working completely fine (their chip temps are in the high 50's low 60's), I have the exaust from all the miners vented into an attic space and I have a box fan bringing new air into the area for the miners. 

Any thoughts on where to troubleshoot this?  Power source, internet connection (I'm having no problems viewing the miner on my network or remotely), firmware issue?  Thanks in advance!