hello steve and sougata

thanks for your hints.

i plan to change this three inputs (b5,b6,b7) to change to a2,a3,a5 and renew to code from the interrupt handler to a subroutine.
on the build in board which makes some troubles, the long connection is on b5. b6 and b7 are in the device so about 10cm long.
i will make a separate regulator from 12v to 5v from the same power supply to source a relais. sink them with the long cable outside to ground. this ground is also the internal gnd from the circuit. did you think this is a problem? the relais contact then switch in the device the input a5.

the mclr pin is set with 1k to 5v.

the setup is on a proto-board...

in the actual test circuit i also add a debug_off, with no success.
interesting is that when the pic seems frozen and i read back the codes with melabs serial programmer, the code starts again normal when it is finished...

cheers