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Lego Mindstorms NXT motor port failure? Answered

I just dug out my Lego Mindstorms NXT 2.0 (it was buried under some stuff) and I decided to play with it. I had built it into a "Robogator" model, and I went to test the jaws, and.... nothing. The motors didn't turn at all. They just locked in place. I replaced the batteries, tried test programs, updated the firmware, and even opened up the NXT, but I couldn't find anything wrong. Also, the motors worked when i connected two together and turned one. I called Lego support, but their answer was to just buy a new one. Anyone have any idea how to fix this?


SOUNDS like the output drivers are fried. Have you looked on the web for any fixes ?


Yes, but i couldn't find anything. How could i tell if they were fried?

I'm assuming you know how to write code to drive them properly. If they don't work when you drive them, the obvious inference, since the motors themselves work, is that the driver doesn't.


Do you have any idea how to fix this? Or should I start looking for a replacement?

Open the case, and take some good pictures, perhaps I can help. I don't know yet.

OK, i took some pictures. The board is a 2.0, as well. The "105" chip seems to have exploded, but that could also be a heat-conducting substance.


Can't read chip numbers ! See if you can list them, particularly the ones near the connectors for the motors

The chips are 1930-8ZX, LB1836-8WX1, and one huge 150 (not 105, sorry). The 150 is the big grey-black one. I can take better pics if you need, I found my other camera.

HI. Thanks for all your comments. I was ready to order replacement driver chip and tackle SMD soldering, but on opening up the unit, poking around and "dusting off" the insides I suddenly found the output port starting working, so I suspect a loose connection, probably around where Port A connects on to the PCB, as it's physical.

Turn the motor on with code. Watch the volts on each motor pin: I am expecting one to go high, the other low in the forward direction, and then low/high in the other. If one doesn't change - the chip's dead.


Alright, so i have a dead chip... how do I fix this? Sorry about sot replying for forever, I forgot :)

Buy a new chip
Solder it in place.

Look for some instructions on soldering SMT chips - or find a local shop that will do it - it should take less than 10 minutes.

Don't forget to mark it as best answer.

Where are you in the world ?


Hi, please try/ensure the following
1) is the NXT cable well plugged at both ends
2) do motors in the other 2 ports work? the jaw that is in motor A right? did you try that same motor in port B or C?
3) did you try a different motor in port A (or whatever one is used for the jaw)
4) did you try a different cable? (like swap one from elsewhere on the robot to test)

if all other motor work in all the A, B and C port then you have a dead motor!!
if no motors work in one single port,,, like A for example then you may have a bad NXT motor port and that is the worst case as it means you may have a damaged NXT brick.

Please let me know the result of those test
I may be able to help you further so don't despair


Ok, so i tested each of the motors, and none of them move when the program was run. Also, the motors DID work prior to this, so I don't think the program's the problem

if none of the 3 motors work then the problem is not the motors!
the odds of 3 motors dying on you are next to none.

If you did not use the NXT brick for a long time and you had to change the battery to hear the start up sound... chances are the program got deleted from the memory

if you have NXT-G installed on your computer i strongly suggest you upload the program again into the NXT and make sure all your cables are plugged in the right motor ports ( A B C )

if you don't have NXT-G on your computer use the built-in test tool in the NXT brick:
go to the NXT Program menu
plug motors in port B and C
in the 5 empty square put -- up arrow, wait 2sec, down arrow, wait 2sec, loop -- and press RUN

Tried both, and still nothing. I think this might be a hardware issue, not a software one. Thank you for your help though. :)