I am having an odd problem rebuilding a printer in getting the bed to start. It has Marlin and a new RAMPS 1.4.

I got an old SSR to control the bed as the RAMPS 1.4 I replaced started to smoke and go black around the contactors.

I got the nozzle working and calibrated, but the bed does not seem to turn on with 0V going to the D8. The LED doesn't turn on. I tried a M106 S255 to turn on the D9 and the LED turned on great. I was reading and thought maybe the mosfet was toast, so instead of jumping the gun I went to pins_RAMPS.h and changed the pins below:

Quote

#if ENABLED(IS_RAMPS_EF // Hotend, Fan, Bed
#define FAN_PIN RAMPS_D9_PIN
#define HEATER_BED_PIN RAMPS_D8_PIN

Fired up the machine with the new code, tried to turn on bed, nope. Turned on fans and yep. The D8 LED turns on for fans but D9 won't turn on for bed.

What can prevent the bed from turning on?

Other things I ensured from configuration.h

Quote

#ifndef MOTHERBOARD
#define MOTHERBOARD BOARD_RAMPS_14_EFB
#endif

Edited 1 time(s). Last edit at 02/07/2018 10:46PM by BlenderGuy.

Check the bed thermistor, if it doesnt read sane values, it wont let you turn on the bed,