Unplugging the USB cable does not power off ROV


When I unplug the USB cable, the ROV continues to run, and I have to take the batteries out to turn it off. Any suggestions on how to resolve this? Thanks!


So to debug this you’re probably going to need a voltmeter and a copy of the schematic for the controller board. You can download a pdf copy of the schematic from our GitHub site here. Do you have a good voltmeter that you can use?



Hello Katie,

That is strange. Did you happen to receive your ROV secondhand, or did you get it new?

There is actually a couple of blank pins on the controller board, J12 - it should say Pwr switch. These are incorporated into the design so that you can bypass the 5v power switch and power on your ROV with just batteries in. This should be opposite side of the controller board as the ESC’s. Please check that these two pins are not bridged.

Nima Torabi
OpenROV Support


@Walt_Holm I have a good voltmeter that will do the job and downloaded the schematic. What’s the next step?

@Support The graduate program that I am in purchased the ROV new from OpenROV store. I will take a look at the pins.



Hi Katie:

So the part of the schematic you need is Sheet 3. The power supply switching happens with optocoupler OC1, MOSFET Q1, and the components in between.

When a DC voltage is applied to the tether, optocoupler OC1 pulls the gate of Q1 down near ground, turning it on and allowing current to flow. If your robot is on without power being on the tether, then either Q1 got fried somehow, there is a short on the board somewhere, or something else is pulling the gate of Q1 low.

OC1 is located on the corner of the board opposite of the DB-25 connector. Next to it is jumper slot J12, which can be used to manually turn on the robot. As Nima mentioned earlier, there should not be any jumper soldered in the J12 position. With batteries in the robot but no connection to the tether (the ROV should be erroneously turned on right now) measure the voltage across the two pins of J12. On a good robot you should see something close to battery voltage (say ~9V). If OC1 is improperly turned on you’ll see maybe 0.8V or so, and if there’s a short here you might see something that is essentially 0 volts.

Let us know what you find and we’ll move on from there.



@Walt_Holm @Support
There is no jumper soldered onto J12. In my search for Q1, I noticed that Q4 is completely fried. Could this be why the ROV does not power off correctly?


Hi Katie:
Q4 is the driver for the internal lights. When you had the short-circuit on the light board, that’s when Q4 probably fried. You can see Q4 on sheet 6 of the schematic.

Maybe the short-circuit that damaged Q4 also damaged Q1, the main power switch. Can you remember whether the ROV turned on the very first time you put batteries in it, before you had attached the topside tether connection?

Anyway, please go ahead and look at the voltage across J12. If it’s something close to battery voltage,but the ROV is powered on, then Q1 is likely damaged.



Hi @Walt_Holm,
The voltage across the two pins of J12 was 0.3V. That means that Q1 is ok and OC1 is at fault? That is something defective with the controller board?

The first time the ROV powered on was just with the batteries. I attached the topside tether connection after that and successfully opened the Cockpit.


Hi Katie:

That is a curious result, as it seems to indicate that something is powering the optoisolator OC1.

So if you hold your controller board with the DB-25 connector on your left, OC1 is right underneath J12, and pins 1 and 2 of OC1 are on its left side. With batteries in the robot but the USB cable disconnected (the ROV should erroneously be on at this point), measure the voltage between pins 1 and 2. It should be 0 with the USB cable disconnected. If there’s a voltage there, then that would explain why the ROV is on, and then it’s just a matter of tracing the signals to find that voltage.