Brakes will not release

Good morning,
I am working with IRB4400/S4c. I have been attempting to work thru an issue involving brakes not releasing. I can verify 24v to ground at each motor for brakes. No reading from 0v to 24+. Push buttons do not respond although there is 24v at the buttons.
I am working with IRB4400/S4c. I have been attempting to work thru an issue involving brakes not releasing. I can verify 24v to ground at each motor for brakes. No reading from 0v to 24+. Push buttons do not respond although there is 24v at the buttons.
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It sounds like you may have a broken core in the cabling up the robot.
The 24 VDC to the buttons should be present at all times when the controller is powered up (ie it does not go via the brake contactor), so you should get 24 VDC on the motor side of the button when you press it (measured at the button).
If that is correct then there must be a cable break from there up the robot.
Multiple axis not working sounds like power to brake system or main power to controller/drive unit - but the controller should report errors if there was under voltage....
With manual release of the brake you should be able to move axis 1, 4, 5, 6 one at a time by hand (2 and 3 will drop on a large robot like the IRB4400 so not safe to try a manual movement of those two).
If there is still any doubt about the brakes get a known good 24 VDC bench power supply and connect it directly to the brake at the motor power plug - again axis 2 and 3 will drop so unless you can support these axis safely do not release their brakes.
I would have the controller power off (and locked out), also the robot power plug at the base of the robot unplugged to isolate the controller completely....
This will eliminate the robot wiring, power supply in the controller, etc - if above test (moving axis by hand with external power supply connect directly to brake at the motor) shows the brake is now operating correctly then move the power supply down to the brake pins in the power connection plug on the base of the robot.
Needless to say caution is required to connect to the correct pins in the plugs and not short out to any neighboring pins.