Hot End won't turn on ??

I have a newly built reprap printer built from a web posting and my tenacity. (repalmakershop.com) The build is complete and I have tested every system/function with success except one, the hot end will not turn on when called for on the TFT touch screen. Literally all other things work. Jogging, Homing, Hot Bed, Fans, Extruder cold end. Just the hot end will not turn on. I have replaced the MKS sbase 1.3 32bit board. (problem persists) I have replaced the TFT control screen. (problem persists) I have gone through every single wire. I can heat the hot end if I pull the feed wires to the head off of the MKS board terminals and use an external power supply. It heats, the thermistor registers correctly, the fans turn on and off on heat up and cool down. I just cannot get 12vdc to show up at the control contacts on the MKS board to power the hot end?? I'm including a link to the config file on the developers github site. Maybe there is an error I can't see but all other things work? I have made the developer aware and he has proposed common things like check wiring (done) test for correct power to MKS board (done), on and on... things that have made no difference. This is a subtle problem. Please help if you can. I would love to get printing!
[github.com]

When you use a digital volt meter at the hot end terminal, do you see 12V when the hotend is commanded to turn on without the heater connected? Is the hotend in working order, no short circuits?

Is there a second extruder heater connector, did you try that? Check if the function isn't swapped between hot end 1 and hot end 2.

Did you check the 12v psu, is there a fuse, is it seated ok and still working?

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

No. With the wires running to the hot end removed from the board and the tft screen calling for heat no 12vdc is present. Yes the head is in working order. I can connect an external 12vdc power supply to the wires removed from the MKS board coming from the hot end and the hot end will heat normally. No short circuit. The hot end thermistor also registers the correct temperature on heat up and cool down. There is only one extruder. The main power unit is 24vdc to power the heated bed and then splits off into a boost Buck unit to reduce the 24vdc to 12vdc. Yes the 24vdc is correctly feeding into the MKS board. There is a fuse but it is fine. All power is available.

The second unused extruder terminals are being used to turn on a 12vdc hot end cooling fan at 40c and likewise shut the fan off when the hot end cools below 40c.

You could remove the fan and put it on a constant 12V supply (or use a manual pwm controller) and use the second terminal to print. Or swap the pin assignment and you can at least start printing until the issue is resolved.
It sounds to me it's a firmware issue. Or something is wrong in the gcode used to turn the hot end on or something.
Maybe there's a setting to first enable the hot end before it can be used as a safety feature? Did you try running pid tuning? Maybe it needs this before being able to turn on?

Is it possible to downgrade or upgrade the firmware?

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]