If it was me, I'd replace the 5V cap and the header pins on the power supply.  Those round header pins are crap.

Done already... ( header pins ) The 5 volts to the MPU board is between 5.01 and 5.05 v, i'd consider that clean )

Just to recap a bit - do you have the 5V at pin 37 on interboard???

No 5 V at pin 37 !