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Basic Troubleshooting for Motor Drivers


STATUS LED is not coming on.

Make sure you have at least the minimum input voltage specified for the motor driver at the driver's B+/B- terminals. If minimum voltage is present, there may be a problem with the on-board 5V regulator and/or the processor chip and the driver will need to be repaired or replaced. Make sure power is not back-feeding into the driver's 5V terminal.

If the driver is bolted down, loosen the mounting screws. If this causes the Status to come on, there may be a problem with the board shorting to the heatsink. Contact Support to resolve this issue.


STATUS LED is on, but there is no motor output.

If DIP 3 is OFF for battery protect mode, make sure your battery is not in need of re-charging. If any one of your battery cells is 3V or less (for a 2x32 this voltage can vary depending on the battery type selected in DEScribe), motor output is shut down.

For all drivers except 2x5RC and 2x12RC, check for motor output in analog mode. Disconnect the motor driver from the circuit. Set DIPs for Analog Independent mode (4 OFF, all others ON for Sabertooth; all ON for Syren). With nothing connected at the signal terminals, connect at least required minimum voltage at the B+/B- terminals and check the motor outputs for voltage. If you do not have a volt meter, you can briefly connect the motor leads to an output channel. If voltage is present, the motor will spin full throttle.

If there is no motor output voltage, the driver may have sustained damage. If there is motor output, verify the proper signal is being sent to the driver for the input mode you're using. 

For RC-only drivers, make sure your receiver is powering up (either with the Sabertooth 5V BEC or a separate battery- never both) and sending servo signals.


LED behaviour pertaining to input voltage.

When input voltage is just outside the range specified for the motor driver, the LEDs will indicate:

Syrens: Both Status and Error LEDs will glow if voltage is too high. If voltage is too low, no LEDs will be on.

Sabertooth 2x5 (both versions): Both blue and red LEDs will glow if voltage is too high. If voltage is too low, no LEDs will be on.

Sabertooth 2x12 (both versions): If voltage is too low, Status 1 will glow, Status 2 and Error will flash. If voltage is too high, Status 1 and Error will glow.

Sabertooth 2x25:  If voltage is too low, Status 1 will glow, Status 2 and Error will flash. If voltage is too high, Status 1 and Error will glow.

Sabertooth 2x32:  If voltage is too low, Status and Error will flash. If voltage is too high, Status and Error will glow.

Sabertooth 2x60: If voltage is too low, Status will glow, Cells and Error will flash. If voltage is too high, Status and Error will glow.


These LED behaviours are not exclusive to battery input. Sometimes a flashing or glowing Error paired with a flashing or glowing Status can indicate software or hardware damage.



An Error indication should not be ignored. If it is determined that the error is not due to an input voltage issue, there are three common scenarios to investigate.

1) A flashing or flickering Error LED is usually a sign that the motor driver is current-limiting. This is likely most noticeable during stalls or increasing speed. Either the motors are drawing too much current for the driver to handle, or the driver cannot sink the regenerative current into the supply. Make sure the battery has enough capacity to handle the motor current draw during periods of peak operation*, and make sure that any other components (such as a switch) are rated a high enough current to handle the draw.

*Another common cause of current-limiting is using a DC power supply unit without a battery in parallel. A PSU cannot sink the regenerative current from the motor driver, so a battery must be put in parallel. (The Sabertooth 2x32 has a built-in voltage clamp which allows it to be used with a PSU alone. See the datasheet for more information.)

Ignoring excessive current-limiting and/or using a PSU without a battery in parallel can lead to damage such as firmware corruption or processor damage.

A flashing Error can also indicate a short has been detected or sustained- see #3.

2) A glowing Error LED combined with no motor output and a hotter than normal motor driver usually means the driver has gone into thermal shutdown to protect itself and the motors. Turning the driver off and allowing it to cool resolves the issue. If this is a frequent occurrence, the driver may not be powerful enough for the application, or is in need of more airflow or heatsinking. See the motor driver datasheet for more information regarding proper mounting techniques.

3) A glowing or flashing Error LED during power-up and/or when a command is sent to the driver can be an indication of hardware damage- most likely due to a short detected or sustained on a motor terminal. Disconnect the motor(s) to see if the Error ceases. If so, verify the motor is in good working order and that it has been correctly wired to the motor driver. If the Error persists without motors connected , then it is likely the driver has sustained permanent damage and will need to be repaired or replaced.


Other types of LED indications.

A flickering Status LED can indicate the on-board processor (which gets its power from the on-board 5V BEC) is losing power. This is known as a "brown-out." This could be caused from too much current draw on the BEC. See the datasheet for your particular motor driver for BEC power specifications. If you are powering something more than a receiver, potentiometer, or microcontroller with the BEC, disconnect it to see if that remedies the issue.

A brown-out can also be caused from loss of power on the battery side. Meter voltage on the motor driver B+/B- terminals to check for extreme voltage drops. A voltage drop could be caused from an insufficiently rated power switch and/or insufficiently rated or old batteries.

A brown-out in RC mode will cause the servo signals to be re-calibrated if you are using the auto-calibrate feature. This results in an erratic or unresponsive robot. Be sure to test your robot safely before releasing it into the environment.


Glowing or flashing Error and Status LEDs may indicate the firmware has become corrupted or damaged. This is most often due to a previous Error state. If the motor driver has not smoked or caught fire, and isn't drawing excessive current and becoming hot when powered, the firmware EEPROM settings can be reset on certain models of motor drivers. This requires our DEScribe software and a USB to TTL serial converter for interface to a PC:

The following models are DEScribe compatible: Syren10, Syren50, 2x12 (advanced version), 2x25, 2x32 (does not require an external serial converter), and 2x60.

Resetting the EEPROM does not always repair the corruption. If the firmware is too severely damaged, as can be indicated by a failure to connect with DEScribe, the driver will need to be repaired.

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Article details
Article ID: 16
Category: Motor Drivers
Date added: 2016-05-04 21:29:15
Views: 69331
Rating (Votes): Article rated 4.5/5.0 (110)

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