3pi Not Turning On

My 3pi won’t stay on. I push the power button and the LEDs flash on for a fraction of a second then go off. The robot does not start up. I’ve checked all of the solder points to make sure nothing has fallen onto them or anything. I’ve also tried several different sets of batteries. Help please!


I have a few questions that can hopefully help narrow down what’s going on:

  1. Did your 3pi exhibit this behavior out of the box or did it originally work for you as expected? If it’s the latter, what was the most recent thing you did with the 3pi before this behavior started?
  2. Is the LCD is correctly plugged into the 3pi. Does the problem persist with the LCD removed?
  3. What kind of batteries are you using? Are you sure they’re new/charged?
  4. Do you have any non-standard connections to your 3pi? Have you soldered anything to the board?

- Ben

  1. It originally worked. Most recently I connect a servo board to the serial terminals (PD0 and PD1), GND and a servo power connection to VBoost and GND (with V_Servo = VCC bridged on my servo board). This worked, but anytime I tried to move the servo it overloaded the 3pi and it shut off and then snapped back on. I also had a simple PIR motion sensor on PC5 (w/ jumper removed) and powered off another VBoost and GND terminal. Everything was fine until I removed the VBoost and GND wire for the servo power (and replaced with an external 4xAA battery pack connected straight to my servo board). I then added a connection to VBoost for the VCC input on the servo controller and this seems to have caused the problem.
  2. This problem occurs with and without the LCD
  3. I have tried several sets of (non-rechargeable) AAA batteries from different packages and it still occurs
  4. As mentioned above I hooked a servo control board up, but since this problem occured, I desoldered everything and it’s still not working.

My next step is to take a multimeter and make sure none of the voltage terminals are shorted to GND, since that’s what this seems to indicate, but would really appreciate if there are any other ideas…


A few quick notes - I am sure Ben will say more later:

  • You are wasting Ben’s time by not mentioning the things you did that broke it in the initial post. How do you expect someone to help you without knowing these crucial facts?
  • VBoost is ~9.25V. This is way out of range for a servo or for VCC on our micro serial servo controller.
  • You cannot say “everything was fine” if your 3pi was shutting off every time you move a servo.
  • A GND connection between communicating devices is always required
  • You shorted your 9.25V to the 4xAAA battery pack through the VCC=VS jumper, right?
  • Even with no GND connection, the 9.25V on VCC will cause the Micro SSC’s TX line to reach 9.25V, which could damage the 3pi’s RX line.

Some clear, high-resolution pictures of the board might help us identify problems that could be fixed, but it really sounds like you have been doing your best to destroy your 3pi, so I do not have a lot of hope!


Hey Paul… let me start out by appologizing if I wasted anyone’s time. The reason I left out the details in my first post is that I don’t expect anyone to review the details of my add-on HW, since it is def. outside of the scope of the 3pi. I was mostly just hoping to get some friendly advice if anyone else had seen a similar problem from like a connection coming unsoldered or a component failing, etc. I got this little guy for Christmas from my gf so I’ll feel awful if I toasted it. I have a degree in mechanical engineering so I know enough not to do anything really stupid.

Let me start by going step by step through what I did:

  1. Received 3pi and played w/ demo program (everything worked)
  2. Did some small custom programs (new LCD messages, made the motors dance, etc)
  3. Decided to add a PIR motion sensor. Soldered to input PC5, GND, and VBoost (can take 5-12V power). Program worked fine to sound a buzzer alarm when sensor tripped.
  4. Decided to try to add servo. Wired V_IN and GND on the servo board to V_Batt and GND on the 3Pi. Wired the serial TX and RX on the servo to PD0 and PD1. Jumpered the Vcc=Vs on the servo board (so VBatt from the 3pi was powering the servo board and the servo. I misspoke before about this being VBoost)
  5. Tried the HW above and found that whenever the servo moved, too much current was being drawn from the AAA batteries to supply demand and the system would power off, but could be powered back on. Everything was “fine” in that nothing should have been damaged… I just didn’t have sufficient power to source the current the servo needed so the system shut off.)
  6. Put my 3pi away for a couple months and didn’t play with it (never thought to power it back up to see how things were before making changes 7 and 8 below. I left it in a working state.)
  7. Decided to add an external battery pack for VS (Servo power) on the servo board. Removed the VS= VCC jumper from the servo board, wired VCC and GND of the servo board to VBoost and GND. Left PD0 and PD1 connected to the serial TX and RX on the servo board (so there were only 4 connections between 3pi and servo board… I did NOT short the battery back to the VBoost. The jumper was removed first and foremost)
  8. Tried to power on the 3 pi (with the servo board connected to the 3pi but no battery pack on the servo VS yet) and found the behavior listed where the power and LEDs blink on and then shut off.
  9. Disconnected all wires from the servo board side so that I just had wires with connectors on the 3pi. Still saw immediate powering off.
  10. Tried several sets of batteries. Still saw immediate powering off.
  11. De-soldered all of the wires that I added. Still saw immediate powering off.
  12. Reviewed board for any shorted bits of solder, wire trimmings, etc. Found nothing.

All of the soldering I did was in the prototyping space and the connection pads for option expansion listing in Chapter 9 of the user manual.

Again I apologize for not delving through all of the details before, and I appreciate you asking for them, but I never expected support for prototyping work I was doing outside of the 3pi itself. Thank you for any advice or thoughts you can give me!

Unless this was some kind of monster servo that was trying to move a hefty load, VBAT should have been able to provide sufficient power. This tells me that either your batteries were very drained or something was connected wrong.

As for the “wasting our time” comment, paul means that it’s extremely relevant to mention things like “it was working before” and “the last thing I did before it stopped working was connect an external peripheral that caused the 3pi to shut off when used”. Otherwise, it’s a much more open-ended problem and we have to spend time trying to narrow it down. You don’t need to include every detail in your opening post, but the two short sentences in quotes above would have made a great addition. We’re happy to help you try to get your robot working again, no matter what you did to it.

From your description of events it sounds like you never actually connected your second battery pack to anything because you noticed problems with your 3pi before you go to this step. Is this the case? Is there any chance you accidentally shorted something while you were making your solder connections on the 3pi? Were batteries in the 3pi while you were soldering? Can you post some high-resolution pictures of the top and bottom of your 3pi PCB? Maybe something will jump out as a potential cause. My current suspicion is that there is a short somewhere on the board that is keeping it from turning on. If so, the big question is whether that short is external (and fixable) or the result of a damaged component on the board.

- Ben

I tried today at work but I don’t have a camera good enough to get anything but blurry shots of the 3pi.

Inspecting it myself I don’t see any burned traces or components or any solder anywhere it shouldn’t be.

I took a multimeter and none of the Voltages are shorted to ground nor to each other. I think I might be more or less up a creek, unless you know of any suspect locations on the robot that are likely points of failure.

Is there a complete circuit diagram available anywhere? I checked the manual but didn’t see it.

If there is nothing left for me to check\try to fix, I’ll learn from my mistakes (soldering when pressed for time at 11 at night being one of the first), scrounge the motors and what not from the chassis, and probably order a new 3pi so I can keep building and programming (and so my gf doesn’t get bummed that I broke the present she got me for Christmas.) :frowning:

I appreciate the help guys!

Sorry for my delayed response. We’d be happy to take a look at your 3pi. If you’re interested, please contact us directly for an RMA number.

- Ben