C740A0 - Hardware monitoring critical problem


I work with a new UR10e with an OEM DC control box and a teach pendant with polyscope 5.11 software installed. After connecting and enabling the teach pendant I am receiving a C740A0 error when trying to turn on the UR10e via the teach pendent. The robot is fed via a 24V 30 amp power supply.

did anyone encounter such a problem?

I have found a similar issue but with no real solution in the comments


ur_20225290051_2022-05-30_17-05-36.zip (2.6 MB)
Attached to this comment is the error log file.

Hi lior,

I looked at the log_history.txt
I found this: 48V voltage is outside of the allowed range: 39.89
It happens immediately after you try to power on the robot arm.

Is it possible that your power supply cannot deliver current fast enough?
Did you consider this notice?

Hello Jor

Thank you for your response. thanks to your input i have found the problem and was anble to operate the robot. The problem occured, as you have said, due to lack of ability to provide the required current to the UR system. This current limitation was created due to an inrush current limiter which was installed on the robotic arm.

here is a link to the current inrush limiter which was used: https://www.mouser.co.il/datasheet/2/600/ametherm_MM3_%201R050-DIN-1214946.pdf.

additional information to others that would adress this problem:

  • control box: OEM DC
  • Input voltage: 24VDC
  • robotic arm used: UR10e
  • inrush current limiting component: Ametherm MM35 1R050-DIN

Thank you again for you help and have a great day

How did you wire in the inrush limiter on the control box?

I solved my issue regarding the same error code. Turns out my supply was not pushing out enough voltage. I was at 24~25V and after turning it up to 27~28V it was able to engage. The controller states 19~72V so I was a bit mislead and suppose I forgot to compensate for the robot draw in of its self. Current drawn seems to be ok with in this range.

Im using a U16e by the way.

Hey Sorry for the late reply.

Regarding the wiring of the Inrush limiter I have connected it in series upstream to the control box.
My guess is that the problem for both of us was that, before the robot is started, the current running through the Inrush limiter was low and thus the temperature of the resistor (which is the Inrush limiter) was low and the resistance was close to 1 ohm, which limited the current supply to the system and caused a significant voltage drop somewhere in the system.

Although this is wierd to me i believe that that is the reason.

Jor, would you suggest creating a bypass to the Inrush limiter that will be triggered a few seconds after the robot is powered up? how would you suggest solving the voltage drop issue (beside raising the voltage or getting rid of the current lnrush limiter)?

Hi lior,

I would suggest that you use an oscilloscope to measure.

  • Does the supply deliver 24V ? Did you damage your supply during initial testing
  • What happens with the supply when you power-on the robot ? Does the supply shutdown when too much current is drawn
  • How big is the voltage drop across your thermistor ? Consider different “soft starter”
  • How big voltage drop is there across the wires from the supply to the robot ? Consider using shorter thicker wires
  • Is there a loose connection ?

Continuing the discussion from C740A0 - Hardware monitoring critical problem:

Hi Iior,

I have just purchased a MM35 1R050-DIN to solve same issue I am having on OEM controller DC version, am I correct say that two poles of the limiter need to be wired into my circuit breaker live side? As we have single phase 240V with 2-pole (L and N) circuit breaker that is protecting the controller.

Your reply would be much appreciated. Thank you

Continuing the discussion from C740A0 - Hardware monitoring critical problem:

I have wired the inrush current limiter but that did not resolve my issue having hardware monitoring error code C740A0, I don’t know how to proceed next.

I have connected the MM35 1R050-DIN on the circuit breaker live side and every time i’ve started the robot i’ve got the C740A0 error. the reason was that, when starting the robot, the current running through the circuit caused a major voltage drop on the thermistor (the MM35 1R050-DIN).

The problem is that, when the robot is turned off, the current running through the thermistor is not enough to heat it up and reduce the thermistor’s resistance. we have solved the issue by creating a different soft start circuit which we have developed. the main idea was that, when turning on the power to the OEM controller, we have connected 1 OHM resistors on the DC source Vin and then, after powering on the control box, we have bypassed the resistors to allow for the higher currents which are required for operating the robotic arm

hope this helped you, have a good day

Hi Iior,

Thank you for your reply.

So you’ve resolved it by added a 1ohm resistor on the + side of DC source? Do you connect the resistor in series of the Vin? Just to clarify it is Vin not Vout? Also do you still use MM35 1R050-DIN in your soft start circuit?

Appreciate your help. Thank you.


I meet the same issue (C740A0) with an UR10e powered in 230VAC (standard controler).

If someone have found how to fix that, I will appreciate your helps.
Thank you.