Sunday, December 28, 2014

Fixing USB on a Lego Mindstorms NXT Brick

My son has a Mindstorms NXT set where the center post in the NXT Intelligent Brick's socket broke off, resulting in an unreliable connection with the computer when downloading programs. Replacing the Brick will cost $170 from Lego Education, so I decided to open it up and see if I can fix it. It turns out that, other than figuring out how to take it apart, the repair job is not too difficult.

This article is for informational purpose only. Open up your NXT Brick at your own risk. If you have a problem with your Brick, call Lego technical support first. They may replace it free of charge, particularly if it's under warranty.

The tools you need are:
  • Soldering iron
  • Desoldering tool
  • Solder
  • Phillips screwdriver
You'll need to purchase a USB Female Type-B Port 4-Pin socket to replace the broken one.

Opening the NXT Brick
  1. Open the battery compartment and remove all batteries. Remove 4 Phillips screws holding the battery compartment to the top white shell of the NXT brick. Gently pry off the top shell.
  2. Unscrew 2 Phillips screw holding the LCD display and the circuit board to the battery compartment. Gently pry apart the USB side of the Brick and remove the gray plastic port covers on both ends so that you have enough space to desolder the underside of the USB socket. 
The circuit board will NOT come off completely! The non-USB side has two posts soldered to the battery terminals inside the battery compartment. You may desolder these to take off the entire circuit board but it is not necessary.
There is a rubber button that makes contact with the circuit board through a hole in the battery compartment. This is used to tell the NXT brick that a rechargeable battery is being used. Do NOT lose this!

Replacing the USB Socket
  1. Desolder the USB socket. There are 2 tabs and a cluster of 4 small terminals that must be desoldered. Use a desoldering tool to suck off the solder so you can pry off the broken USB socket. Be careful not to damage the circuit board.
  2. Insert the new USB socket and solder the terminals and tabs back. Test USB connectivity with a computer using Mindstorms NXT program before putting everything back.
Putting It Back Together
  1. Insert the port covers and put the rubber button in place. Be sure to align the port covers properly. Push the circuit board back on to the battery compartment. A little effort may be necessary. There are 2 posts on both ends of the battery compartment that snaps into the port covers.
  2. Screw the display and the circuit board on to the battery compartment.
  3. Slide the white shell on to the top of the Brick via the guides on the port covers. If you took out the front buttons, be sure to put them back before putting the white shell back. Use a little force to snap them together.
  4. Turn it over to see the inside of the battery compartment. Ensure that the rubber button is in place. Put the 4 screws back.
  5. Test your new USB socket by downloading a new program.