Now I'm really confused. I've been following this thread for a while and was completely expecting my batch two z9 mini's to underperform compared to batch one. I received two of them on the 10th of September.

But they're not underperforming. They're as good as batch one. Both of them. Both easily clock to 750 and have been averaging 16.5 KSols/s for the last 24+ hours.

In case it benefits anyone in the community, these are the exact steps I took and the results:

• Changed pool configuration. Set fan speed to 100% fixed.
• Initially tried the F12 trick to overclock the first one. Tried 750 off the bat. Didn't work. As in, the firmware still showed the machine running at 500M.
• Tried editing cgminer.conf directly (after granting it write permissions). Didn't work. The firmware still showed the machine running at 500M.
• Tried 600, 625, 650 with both methods above. Still didn't work. At this point I figured the firmware was locked to 500M. Didn't try 550M. Double checked cgminer.conf. It was correctly saving whatever frequency I put in it but the machine just wouldn't accept it. New firmware? Probably.
• Flashed firmware to one dated may 26th 2018. I had downloaded this from Bitmain way back just as a backup. Filename: Antminer-Z9-Mini-201805262047-500M.tar.gz
• Overclocked to 750M. Works perfectly as mentioned above.

I'm wondering if I was just lucky and got two good units but it doesn't seem probable considering the fact that the firmware I received was the one with the "Balanced" option on it. It had no option to overclock.

The only thing I seem to have done (maybe differently) is set fan speed to 100% fixed. Maybe that has something to do with it?

Worth a shot I guess.

EDIT: Forgot to mention - temperatures on all boards are between 65-70 degs with the fans at 100%.