Table of Contents

• Overview
• Symptoms
• Diagnosis
• Parts

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'",

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:

• Multimeter setup:
  • Switch to DC Voltage Mode --V
  • Ensure the black lead is connected to "COM"
  • Ensure the red lead is connected to the right hole labeled "VΩHzLive"
• Measure the voltage between:
  • Large copper GND busbar and large copper 48V busbar. Should read ~50-57V
  • Large copper GND busbar and GND post on AltSCC/Tray Brain. Should read ~0V
  • Large copper GND busbar and 12V post on AltSCC/Tray Brain. Should read ~12V
  • Large copper GND busbar and 12V post on the Green/Red Tray Controller Breakout (if AltSCC installed). Should read ~5V
  • The GND post on AltSCC/Tray Brain and 12V post on AltSCC/Tray Brain. Should read ~12V
  • The GND post on AltSCC/Tray Brain and VBUS post on the Green/Red Tray Controller Breakout (if AltSCC installed). Should read ~5V

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:
  • Large copper GND busbar and large copper 48V busbar. Should not beep
  • Large copper GND busbar and GND post on AltSCC/Tray Brain. Should beep (unless isolated 48V -> 12V converter is used)
  • Large copper GND busbar to 12V post on AltSCC/Tray Brain. Should not beep
  • Large copper GND busbar to backplane. Should not beep.
  • The GND post on AltSCC/Tray Brain to 12V post on AltSCC/Tray Brain. Should not beep
  • The GND post on AltSCC/Tray Brain to backplane. Should not beep
  • M+ on AUXMC to Backplane. Should not beep
  • M- on AUXMC to Backplane. Should not beep
  • M+ on LMC to Backplane. Should not beep
  • M- on LMC to Backplane. Should not beep
  • M+ on RMC to Backplane. Should not beep
  • M- on RMC to Backplane. Should not beep
  • Modem frame to Backplane. Should not beep

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
  • 
• Begin disconnecting all USB devices from the USB Hub and Pi, starting with the side cameras and axle/caster cameras
  • After each disconnect, recheck continuity and the kernel logs to see if the issue has been resolved
  • 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

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)

Tray Brain (on new LCRs) - 004679

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

Motor Controllers - 003007

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

Busbars - 002770

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