Spindle won't turn off

I have a YOOCNC pw2034 board. The spindle runs at full speed regardless of the speed control potentiometer or even the Spindle on/off switch. The board or the components don't have any obvious burn marks and the fuses are intact. I have disconnected both the on/off and the speed control and it still runs.

I found the schematic from another discussion (https://www.cnczone.com/forums/chine...er-burned.html) and I have attached it, but my electronics is really rusty.

Any suggestions where to look? I appreciate any help.