# By symptom

| Symptom | Likely cause | What to do |
|---|---|---|
| Nothing happens at the power button | No 24 V; polarity; the button cable | Check the supply's LED, the GX16 cable, the JST button cable on the board |
| The board turns on by itself when the supply is plugged in | 3.3 V on the programming header (an ST-Link or the adapter is connected); the arm was moved while unpowered | Unplug the adapter; move an unpowered robot slowly |
| The robot cannot be switched off with the button | The same 3.3 V | Unplug the programming adapter |
| Clicks on power-up, but the PC does not connect | Wrong serial port; the test firmware is on the board; Linux permissions | [Communication](https://docs.source-robotics.com/PAROL-docs/1.1/08-troubleshooting/communication/) |
| A joint jogs the wrong way | Direction not set for that joint in the firmware; a motor's wires swapped | [A joint turns the wrong way](https://docs.source-robotics.com/PAROL-docs/1.1/build/firmware-and-first-run/#a-joint-turns-the-wrong-way) |
| A joint does not move at all | Driver not seated or faulty; motor connector; the joint is at its blocker | The test firmware: its driver report at power-on, and whether the motor turns with the others ([The test firmware](https://docs.source-robotics.com/PAROL-docs/1.1/board/09-test-firmware/)) |
| A joint grinds at its end during homing | Its switch or sensor does not trigger | E-stop; [Homing failures](https://docs.source-robotics.com/PAROL-docs/1.1/08-troubleshooting/homing-failures/) |
| Joint 6 keeps spinning during homing | The homing pin is not where the sensor looks | E-stop; set the joint 6 pose as in [Homing](https://docs.source-robotics.com/PAROL-docs/1.1/05-operation/homing/) |
| The pose after homing is off by a few degrees on one joint | A loose coupler, a slipped belt, a moved switch | [Couplers](https://docs.source-robotics.com/PAROL-docs/1.1/07-maintenance/couplers/), [Belts](https://docs.source-robotics.com/PAROL-docs/1.1/07-maintenance/belts/), then [Mastering](https://docs.source-robotics.com/PAROL-docs/1.1/05-operation/mastering/) |
| The robot's position drifts during a program | Lost steps: too fast, too heavy, a collision, a reduced current | Lower the speed; check the payload; home again |
| A joint hums or squeals and does not hold | A driver in error, a lost phase | The test firmware's driver report at power-on (its fault flags); check the motor cable |
| Cartesian jogging stops by itself | A singularity | Jog a joint away ([Configurations and singularities](https://docs.source-robotics.com/PAROL-docs/1.1/theory/configurations-and-singularities/)) |
| A pose from the GUI cannot be reached by MoveCart | The inverse kinematics finds no solution along the straight line | Move in joint space; choose another orientation |
| The robot stutters while moving | The PC misses the 10 ms cycle | [Communication](https://docs.source-robotics.com/PAROL-docs/1.1/08-troubleshooting/communication/) |
| The forearm is hot | Hours of motion at the default currents | [Currents and temperatures](https://docs.source-robotics.com/PAROL-docs/1.1/03-technical-data/operating-temperatures/) |
| The gripper does nothing | Not calibrated; an error latched; the cable | Calibrate, clear the error; the gripper's manual |
| The E-stop has no effect | The PC software is frozen | Switch off the power supply; see [Emergency stop](https://docs.source-robotics.com/PAROL-docs/1.1/02-safety/emergency-stop/) |