I have a ramps 1.4 board originally running with an Arduino Mega 1280 with the FTDI chip. I had fans running off the 12V rail switched off D11/6/5/4 via a simple 2N3904. I have since changed boards to an Arduino Mega 2560 R3 and now none of the PWM pins are switching.
I have noticed about 0.81V differential between the 12V neg on the power supply and the 5V gnd rail on the servos header. I measure D11/6/5/4 to have 4.19V when off and 5.00V when switched on instead of the expected 0V/5V swing on the mega 1280.
Is there a pullup problem with just the mega 2560 in Marlin v1.0? Anybody know where I should look??
