# Dual extruder setup in Marlin

I have a Tevo Tarantula with a MKS Base 1.5 board and dual extruders. I am running Marlin RC8 Tevo Community build for the dual extruder, large bed and SN04 sensor.

All temperature sensors work and give accurate reading but E1 when activated runs at 100% until the overtemps kicks in and shuts down the system. Like I said, it reads proper temperatures through the thermistor it just won’t stop at the set temperature. I checked the MOSFET and there is no obvious scorching or bad solder joints on the MKS board. This leads me to believe it is a mix-up in firmware but, being a bit of a newbie on this, I am still getting familiar with G-code and Marlin.

I have confirmed the correct board is being referenced in firmware from boards.h but looking at configuration.h I just get confused. What I am thinking is somehow/somewhere E1 might be referenced as a fan that is just off or on. Anybody have ideas?

• Is this build what you are using? Jun 2 '17 at 19:38

I am not sure what the hardware config is for the Tevo Tarantula

Make sure your configuration.h file is setup for your hardware. The extruder defines are describe in Conditional_LCD.h

It looks like the configuration.h file on GitHub is configured for a single extruder.

For example, if you have 2 hotends; but, "HOTENDS=2" is not set then the I/O will not be configured for the 2nd hotend. I just looked at the code and if HOTENDS == 1 then the MOSFET_D_PIN will be used to control FAN1 (which sounds very similar to what you are describing that you are seeing).

  #if HOTENDS == 1
#define FAN1_PIN     MOSFET_D_PIN
#else
#define HEATER_1_PIN MOSFET_D_PIN
#endif

• If the tarantula uses a single hotend, don't define SINGLENOZZLE but define SWITCHING_EXTRUDER and (i think) EXTRUDERS=2. Then the code will expect the single hotend to be connected to D10. Jun 3 '17 at 2:48
• Thank you for the direction to go. The setup is dual and I "thought" I had checked that. Jun 3 '17 at 13:21
• "Dual" can mean several things. Do you have two separate extruders (hotends), a (single) mixing extruder, or a (single) standard extruder with a dual filament feeder? Marlin has to be configured for the specific type. Jun 3 '17 at 22:14

So, following on from Mark's answer, in line 298 of Conditional_LCD.h, you would need to change:

#define HOTENDS       1


to

#define HOTENDS       2


I had a similar problem, my documentation was wrong and the heater & thermistor were wired in backwards. Maybe recheck your wiring and even try reversing the temp sensor on your board.

• Do you mean that you swapped the heater and thermistor connections, or do you mean that the thermistor was connected to the right therminals - but backwards? Thermistors and heaters are generally not polarized, and can be connected either way around. They're just simple resistors. Jul 21 '17 at 3:36