Machines that were previously running fine but cannot run after board stacking may not be related to frequency but rather to the BIN (firmware version) used. Try using similar BIN versions, such as BIN4, and check if the A5V1R (ASIC version) is the same.
S9K does not support board stacking.
If the control board is not faulty, please export the complete kernel log and analyze it for further investigation.
1\ Test the diode value and voltage of the 3 transistors Q5,Q14,and Q15 comparing the working hashboard.
2\ Test the DC-DC circuit.Remove all components related to short circuits on the board.
3\ Connect Q5 Pin-G to D3 and inspect the boost section for any issues.
1. Tighten the screws on the power supply copper busbar.
2. Replace the copper busbar with a new one.
3. Replace the screws.
4. Upgrade to the latest firmware.