@way2lo2 Not sure, but I do know the firmware won't go below Z0, if you have your M208 set Z minimum to 0.
That's right. So on the first layer the most you can baby step down by is the first layer height.
For best results the probe trigger height must be accurate. Set it at the same point you use for homing. And use that same point for setting Z0 before generating a heightmap or after doing tilt correction.
If you do need to baby step down consistently you can use the amount used to modify the G31 trigger height to make it permanent.
Setting the M208 Z minima to -0.5 would let you go a bit lower, but use that with caution.
It's a little hard to see on the pics, but your problem description and testing performed indicates the issue is with the SD card slot. Warranty exchange approved. Please contact Filastruder and include a link to this thread as authorization.
Your schematic should work for low PWM frequencies, your 'screaming', whatever that might be, is probably caused by a wiring error. Are you sure you connected the GND's of the 12V supply and the uC board together?
Other than that the circuit is suboptimal; it takes R3 a long time to charge the gate of M1 which increases dissipation. Replacing R1/R2/R3/Q1 with something like a TC4427 would be a better solution.
Regarding PWMming TEC's: you can do that as long as you keep the PWM frequency above 1kHz or so. If you PWM with a low frequency there is too much stress on the thermocouple joints due to them thermally expanding and contracting many times a second.