Voltage Drop at Servo Power Terminal (VRSV)


I recently purchased a Mini-Maestro 18-Channel USB servo controller. I followed all the steps in the guide multiple times and also followed the example projects trying to get a servo to work. I started troubleshooting, then I came across an issue at the servo power pins (VRSV) as shown in the image below.

When measuring the voltage across the servo power terminals I only get around 0.3V, even though my supplied power is 5V. To make sure the issue isn’t from my power supply, I connected the servo power terminal to the USB power by shortening it to Vin using the VRSV-Vin jumper, as per the guide. Measuring again, I also got 0.3V across the servo power terminal. Is that normal, or do I have some sort of issue on my board?

Thanks for taking the time to look over my issue.


What are you using for a power supply? Do you measure the expected voltage across it when it is not connected (just in case, to rule out an issue like having your multimeter on the wrong setting)? How and where are you connecting it to the Maestro?

Note that the VSRV=VIN jumper does not connect the servo power rail to USB power; as the name says, it connects servo power to VIN, which is a separate voltage input on the left side of the board.

- Kevin

Hi Kevin,

Thanks for your reply, and for pointing out my mistake. You are correct, the Vin is not connected to the USB power. I did a false assumption during my checks.

I connected the VRSV to the 5V regulated output from the board, just to test that I can get a servo running and it works fine now.

I guess there is something wrong with my power supply, I’ll look into it or get a more suitable regulated power supply. At the moment I am using an ATX power supply, which gives out 5V which I have fused at 1 AMP. Measuring across the power supply terminals I get ~5V.

Thanks again,


I’ve found out what’s wrong with my power supply. It automatically shuts off if it doesn’t have a continuous load. So I’m going to have to add a high power resistor to keep a continuous load.



I’m glad you figured out the source of your problem; thanks for the update.

Note that it is not a good idea to connect servo power to the 5 V output; when you have the Maestro powered from USB, that voltage is provided directly from the USB 5 V supply, and the USB spec allows for a maximum current draw of 500 mA. Servos can easily draw more than that when straining or starting to move (around 1 A per servo), so you risk damaging your computer if you try to power a servo from USB.

- Kevin