Extruder PCB repair



I bought a “secondhand” extruder and I found two problems:

  1. Heating not controllable, start to heat directly and becomes 270 degr and shutdown;
  2. Step-motor does not change in direction (retract filament).

After many hours searching, measuring and testing I found the causes of these problems. I order new components, put them on the PCB and tested it, and now it’s working fine. I suspect that all these problems are related to cable/connection exchanges between step-motor and heater element. Hope that others can take advantage of these solutions. See descriptions and photo’s below.

Problem 1
The cause of this problem was a defective U3 (AM4953P) dual MOSFET, it has a shortcut between source and drain for the connected heating element. Replacement of SMD chip fixed the problem. See made electrical scheme and PCB picture of U3.

Problem 2
This was a bit more difficult, because the DIR (direction) input was defective (shorten) on the driver board 4988. A driver board swap was the only option, but I discovered different amount of pins (18) between the original and a brand new driver board (like Pololu 4988, 16 pin). The conclusion…2 pins where not used and the rest was exact the same as a Pololu board, so a swap looks feasible. Removing the driver board was like hell, glue underneath and a very tiny workspace. Finally cut the driver board in pieces, unfortunately no hot air gun for making it loose. After soldering an IC-socket onto the PCB, its ready for mounting the new driver board. So no soldering anymore needed for any replacement of the driver board. I set the current limit (80% of 1.5A step-motor = 1.2A as the original board) of the new driver board by changing the Vref. It should be 0.96v, but with VDD=3.3v it comes only to approx. 0.825v. This means the current is limited to 1 amp and 66% below the of max current step-motor. Gives this problems, then I suggest to change the fixed 30K with a 20K resistor on the driver board. Then it’s adjustable to max Vref=1.1v with a maximum current limit=1.375 amp. For now it works fine again. See scheme and pictures.



Good Job @ArTerp !

I have a problem with my Mooz 2. Mooz 2 uncontrolled temperature increasing

Maybe you can give some help!

Best regards!


Please send some pictures about how you did the measurements.


Dear ArTerp,

Finally Dobot technical support reply to me and sent me a new PCB card. I made the change of 3D printing head PCB and made printing test with success. So my Mozz 2 is ready to roll again.

Best regards!