Hello all,
We had the same problem with R30iB controller and M20iA/12L robot.
Error list was:
SRVO-018 Brake abnormal (G1:A:1)
SRVO-018 Brake abnormal (G1:A:2)
We measured the resistances between common wire and all three brake groups on CRR88 connector. Everything looked normal, resistances was normal (between 170 and 340 ohms).
We measured the resistances on every brake on the connector on the robot. The values was as follow: A1 - 340Ω; A2 - 336Ω; A3 - 337Ω; A4 - 991Ω; A5 - 506Ω; A6 - 506Ω.
We meassured with megger A1 and A2 brake wire and common wire for short to ground, but there wasn't short cirquit.
We replaced the cable between the robot and controller.
We replaced the servo amplifier (with new cable). The problem still occured. We measured high voltages between common wire and brake control wires (120-130V) when common wire is disconnected, but the robot was able to move without any alarm.
We put external common cable for brakes to every motor and the robot worked normaly.
Finaly we found that there is short circuit between some of the phases of some motor to common brake wire. There was 2 free holes on the robot connector. We moved common brake wire in another hole in both male and female connector and everithing is working now.
I hope this help to someone. This was realy hard problem to solve.
Best regards,
Mihail