I will test before I move them to water and share if it improves... for now 650Mhz @ 2.6T for 48hr and heat is well managed by the current design just with the few mods I did. Since the new 1397AI chips I ordered have not arrived yet for repairs I will stay away from 650+ speeds as I need these for testing.
That sounds great! I will try rotating the fan, too then.
For what it's worth, my experiment with a loosely positioned 'exhaust fan' did not last long; 8h in, the hashrate dropped to 2.4Th/s again. I'm not sure why, but my chips perform well, for a few hours and then slowly drop further and further. It must be thermally related.
add thermal pads to the bottom heatsinks 1mm @ 13+w/k will have the highest impact in it, those few changes will give you
650@2.5-2.6T stable on a ~120W on stock voltage.
Just to be clear: the bottom heatsinks just cool the PCB? And by default are bolted on without any thermal interface (pads or anything else)?
I'd like to prevent touching the top heatsinks, since I believe there's a chance to rip a thermal pad if you don't screw the heatsink on perfectly straight, which would then connect grounds and lead to magic smoke.
But bottom heatsinks are a mod I may actually do.