Little question, is the 761 test model essentially just a 741 but with a PSU attached to it, similar to the 841? I wasn't able to find much information on it. I love your review style, especially this small documentary of your visit to Canaan. It's not often you get to see how miners are made, especially with most manufacturers being extremely closed-off.
I didn't do a full scale disassembly for the A761 unit, but my understanding is that the control board,
PMU board, hash board design etc. is similar to the A741, but there are more A3212 chips in the A761
and it has a built-in power supply unit with thick wires connected directly from the PSU to the PMU boards.
And steel tube case design is ofc different compared to the A741.