Electronics and Chassis Short Troubleshooting - directedmachines/customer-support GitHub Wiki

Table of Contents

Overview

This page covers diagnosis of a short in the electronics or chassis.

Symptoms

There are a number of symptoms that might indicate a short:

  • A failure of a USB port on the USB hub or Pi:
    • Could indicate a short burning out the USB port
  • A motor controller device disappearing, as indicated in the Drivetrain Wiki, or by the following alert:
    • LEFT_MOTOR: device address opened previously but no longer exists, check for USB disconnects or chassis shorts
  • USB cameras not enumerating, as indicated in the USB Side Cam Wiki, the Realsense Camera Wiki, or by the following alert:
    • usbcam-left-color: Capture process returned nonzero exit code: (3.000000) Error initializing the camera stream
  • USB devices continuously responding/not responding, as indicated in the kernel log as:
    • LCR24ZS0-6916625187c4bd849 kernel: [90918.848556] usb 1-1.4.2.3.3: new full-speed USB device number 99 using xhci_hcd
      LCR24ZS0-6916625187c4bd849 kernel: [90918.848807] usb 1-1.4.2.3.3: Device not responding to setup address.
  • A sudden reboot, as indicated in the Kernel log as:
    • \u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000
      Nov 30 09:27:46 LCR24ZS0-698843510034ccf56 systemd-modules-load[141]: Inserted module 'i2c_dev'",

Reproduction

  • A repro of the short must be established before diagnosis continue. If you do not have a repro, work on creating one
    • The repro can be dynamic or static
    • If you fail to create a repro within 20 minutes of trying, ask for help from the R&D team
  • Once a repro is established, diagnosis can continue with a disciplined process of elimination
    • Remove a component, repro, remove next component, repro, ...
    • Continue removing components until the faulty component is found (when the short can no longer be reproduced)

Diagnosis

  • Use a multimeter to test for the voltages and continuity of the following. A manual of our multimeter can be accessed here

Voltage checks:

Continuity checks

  • Multimeter setup:
    • Switch to continuity mode by rotating to the selector to the option with Ω and then presssing "FUNC"
    • Ensure the black lead is connected to "COM"
    • Ensure the red lead is connected to the right hole labeled "VΩHzLive"
    • The buzzer will sound if the resistance of a circuit under test is less than 100Ω
  • Check continuity between:

Frame Sort Pico Tray Diagnosis

Before performing a physical diagnosis, please review frame sort warning, including this presentation

Physical Diagnosis

  • If one of the above tests fail, use the following steps to locate the issue
    • Note the above continuity testing may not find a short inside a USB device
  • Carefully examine all wiring for any breaks, frays, or disconnects
    • image
  • Do a proper shutdown and disconnect all elevator terminals from the Tray Controller (e.g., headlights, modem, usb hub, buzzer, pi power)
    • Check for continuity from the ground of each of these elevator terminals to the frame once unplugged to narrow down the source of the short.
  • If short is in the USB hub or pi, begin disconnecting all USB devices, starting with the side cameras and axle/caster cameras
    • After each disconnect, recheck continuity to see if the issue has been resolved. Kernel logs may also be helpful for internal USB shorts.
    • Use this method to narrow down if a USB device is causing the short
  • Disconnect both antenna SMA connectors from the modem and test continuity
  • Disconnect motor Anderson connectors from the tray and test for continuity between + and - leads of the 175A Anderson connectors to the frame.
  • Disconnect dock anderson from tray and test for continuity between the ground contact plate and the frame
  • Disconnect Molex connectors to the linear actuators and test if they are shorted
  • The latest 3.3.2 Motor Controller can cause a short if it is screwed down too tightly onto the frame
  • If tray brain + motors + dock are all disconnected and there is still a frame short:
    • do a full LCR shutdown
    • unplug the 350A battery connector
    • test continuity between the GND contact on the batteries and the frame
    • Test MC ground shorts
      • Use a wrench to unscrew the ground connection from each of the motor controller BATT- inputs
      • Once removed test continuity between the BATT- posts and the frame. If shorted, the thermal pad may need to be replaced on that MC.
  • A shorted SCC can cause a frame short
    • After a full power down, remove the BATT +/- wires from the SCC and test continuity
    • If continuity is found, the SCC is shorted and should be replaced
    • image
  • Intermittent frame shorts can be caused by the aux motor being clogged with grass
    • Remove the aux motor hat and clean grass from the brushes
    • image

Parts

Here are the parts referred to on this page:

AltSCC (on old LCRs) - 003988

  • AltSCC refers to the entire board (green) with:
    • GND Post (black)
    • 12V Post (red)
    • Tray Controller Breakout (blue) (arrow pointing to VBUS post)

IMG_6691 (1)

Tray Brain (on new LCRs) - 004679

  • Tray Brain refers to the entire board (green) with:
    • GND Post (black)
    • 12V Post (red)

Screenshot from 2023-11-29 16-24-57 (1)

Motor Controllers - 003007

  • AUXMC (left), LMC (middle), RMC (right) with:
    • M+ (red), M- (black)

Screenshot from 2023-11-29 16-36-10

Busbars - 002770

  • GND Busbar (left) and 48V Busbar (right)

Screenshot from 2023-11-29 16-41-03