The connectors for the stepper motor, endstop switch, thermistors and fans on the Duet 2 are Molex KK type. The Dupont-style connectors typically used with RAMPS and other electronics will also fit them. However, for maximum reliability we recommend using the correct Molex female connectors or compatible connectors, because they lock in place and will only fit one way round.

Here are the Molex part numbers for the mating female connectors. These are widely available from the usual electronic component distributors, and on eBay.

• 2-way shell (thermistors and fans): 22-01-2025 or 22-01-3027
• 3-way shell (endstops): 22-01-2035 or 22-01-3037
• 4-way shell (stepper motors, PanelDue and Z-probe): 22-01-2045 or 22-01-3047
• 5-way shell (Z-probe on Duet 2 Maestro): 22-01-2055 or 22-01-3057
• Crimp pins for all of the above: 08-50-0032 (for 22-01-20x5 series shells), 08-50-0113 or 08-50-0114 (for 22-01-30x7 shells)

Alternatively you can use JYK connectors, available in Europe from Conrad Electronics/Rapid Online:

• 2-way shell (thermistors and fans): JYK H2500-02
• 3-way shell (endstops): JYK H2500-03
• 4-way shell (stepper motors, PanelDue and Z-probe): JYK H2500-04
• 5-way shell (Z-probe on Duet 2 Maestro): JYK H2500-05
• Crimp pins for all of the above: JYK T2500-02

The commonly available KF2510 connector kits also fit quite well and include extra pieces for future expansion.

Please note, the shells and crimp pins that we supply with Duets are usually made by Würth Elektronik. The crimp pins made by Würth should only be used with shells made by Würth. In particular, they will not lock into Molex 22-01-20x5 shells.

The large terminals (6.35mm spacing) used for VIN and bed are:

Kaifeng KF635-6.35-2P

this is compatible with the Metz connect 6.35mm equivalent

The smaller terminals (3.5mm spacing) used for the heater terminals other than the bed are:

KF128L-3.50

this is compatible with the Metz connect 3.5mm equivalent

If you short out a PWM fan, the fan driver mosfet will burn out. The replacement part number is PMV40UN2 or PMV40UN2R which is available from the usual electronic component distributors such as Farnell/Newark/element14, Digikey, Mouser and RS. The component identifiers on the board are:

• Fan 0 mosfet: TR5
• Fan 1 mosfet: TR9
• Fan 2 mosfet: TR1

To remove the old mosfet, you will need either a hot air desoldering tool with a small nozzle, or low melting point solder such as ChipQuik . If using hot air, use a shield made from e.g. corrugated cardboard covered with Kapton tape to shield connectors and other plastic components from the hot air. The new mosfet can be soldered in place using a fine-tipped soldering iron, or by putting a little no-clean flux on the pads, placing the new mosfet on top, and using hot air again. Hot air soldering/desoldering is easier if you heat the whole board to about 100-125C on an electric hotplate.

Note when removing any of the heater MOSFETs there is significant heat-sinking into the copper of the board. A combination of hot air rework, Chipquick, and a heated plate may be needed to remove one successfully.

TR2: this is an IPD036N04LGBTMA1

1.04a and later, TR3, TR4: this is an AOD4184A

Prior to version 1.04a it was a IPD036N04LGBTMA1

If you get a short in your wiring between your heater or fan wiring and the VSSA side of a thermistor connection, and you have a Duet 2 board revision 1.0 or 1.01 or a white Duet 2 Wifi pre-production board, then fuse F1 will blow. The symptoms are:

• All thermistors will show as open circuit;
• The resistance between a VSSA pin on a thermistor connector and a GND pin on an endstop connector, which should normally read less than 5 ohms, will be very high (the pins are labelled on the underside of the Duet).

If this happens to your Duet, you should first identify and fix the short. After that, do one of the following:

1. Replace the original fuse with any fast acting 0603 size fuse having a rated current of between 125 and 250mA and a resistance of between 2 and 4 ohms. Suitable part numbers are Kamaya FCC16151AD-B and Littlefuse 0438.250WR. If you choose the Littlefuse part and the old fuse is also the Littlefuse part (recognisable by its metal end caps), you may be able to solder the new fuse on top of the old fuse. Otherwise, you will need hot air soldering equipment to remove the old fuse.
2. Bypass the original fuse with an external cartridge fuse, fitted between one of the VSSA connections and one of the ground connections.
3. Bypass the original fuse with a self resetting fuse as is fitted on Duet 2 board revisions 1.02 and later. Suitable part numbers for the self-resetting fuse are Multicomp MC36207 from Farnell, Bourns MF-MSMF014 and Bel Fuse 0ZCJ0020FF2E. Connect the fuse between the E0 thermistor VSSA pin and the E1 endstop ground pin. Optionally, connect a 10K resistor between the TCK pin of the JTAG pads and the VSSA pin of the E1 thermistor connector, which will allow the firmware to warn you when there is a short to VSSA. Note: the labels on the JTAG pads are wrong, the two columns should be swapped. So the TCK pin is the one labelled GND next to the one labelled TCK. Here is a photograph showing this modification.

The small green component bearing the letters 'bF' is the self-resetting fuse, and the component with stripes is the optional 10K resistor. A piece of Kapton tape was put on the board first to provide additional insulation.

PCB revisions 1.03 and later have a 1A mini auto blade fuse protecting the fan circuits when the fan voltage selection jumper is in the VIN position. Here is an example of a suitable replacement: https://www.ebay.co.uk/itm/20-x-1Amp-Min.... You can increase the fuse rating to 2A or even 3A if your fans, air pumps etc. draw more than 1A in total.

PCB revision 1.04 has the same 1A fuse for the fan circuits and also a 15A fuse for the bed heater circuit and a 7.5A fuse for everything else. These are mini blade fuses. The 1A can be a little hard to find but the other ratings are widely available.

If the TFT panel of a non-integrated PanelDue assembly suddenly refuses to light up, chances are that the backlight inverter chip has failed. This is a 6-pin chip marked L6CE or L6EN or L6GE or similar (the Pin 1 marking bar can easily be mistaken for a letter I in front of the L). The part number is MP3202DJ. It is available from RS Components, Digikey and Mouser, and also on eBay and Ali Express.