Ok, form has answered on that question. one more thing, if you connect fan to the board cut the yellow wire, it will reset PIC16LF1459 all the time. everything else is ok on that side.
@form what we need to change in the code for tach to working ? i have removed it from hardware completely, but it can be used for some alarm when the fan stop working or something like that ... is it big change or minor ? Thanks,
Thats an issue caused by non-standard fans, which actively outputs +12 volts on the tacho-output.
The board is designed for normal CPU-fans (i think it was specified by intel), which have a passive open-collector output on the tacho-pin, which alternatevly connects this pin to GND and leave it open again.
When a non-standard fan outputs +12 volts there, the PIC is entering high voltage programming mode, which is not intended to happen.
So actually no way to avoid it via software, just cut the wire - The software doesnt take care of the RPM anyway.