S4C+ Drive Unit curr controller saturated on irb_4

  • Hello,

    I have a IRB2400/16 with S4C+ bay that has been working flawlessly for couple of years, gone into storage for a year (clean, dry) and now when turning back on gives an error 38653, Drive unit curr controller saturated" on joint 4 as soon as we try to jog it. All other joints move fine.

    I have checked cabling, measured 6.5R between UVW phases of the joint 4 up until the connector going into the Drive Unit 1, DSQC 346E. As motor 4 and 6 are same model I even swapped the UVW plugs between to see if the joint 6 would fail instead but it's still joint 4 failing which seems to indicate the issue would be more on the Drive Unit side.

    The robot config was working fine before so I have big doubts the motor config is an issue. The Controller was fully disconnected while in storage so I am quite flabbergasted that the Drive Unit would die out of the blue without any fault or crash? Anybody hit the same problem, any advice?

  • So after much troubleshooting I got the robot back in operation.

    Followed all procedures initially to check for any connector/cabling issue, insulation tested all motor phases, insulation tested all cabling up till servo drive connector, without any obvious fault, swapped motors/resolvers 4-5-6 and issue was always on axis 4 which lead me to strongly suspect servo drive damage.

    Then I went slightly overboard and got the scope and meters out to study the servo drive unit, reverse-engineered all circuitry, checked pulse trains on the gate drive transformers, all looked fine. swapped the control board between the 2 drives units (the DSP-KORT), same fault, which led me to focus on the power/igbt section and by manually shorting the control pins for the half-bridge gate-driver while applying 24V to the DC rail, where the bus-bar usually goes, I could see 24V on each phases of the 2 other axises, but nothing coming up on the axis 4 section. Checked the board itself, could see all clear voltages on each driver, but no response to input signals, and by inspecting the power section which seems to be supplying the floating supply, fed to the 3 of them I finally found this little blown resistor. Popped it out, frankensteined an equivalent resistor with some through-hole parts, patched it in, booted up and working again like a charm.

    Have to say I went slightly deeper the rabbit hole than I wished, but I got a much better understanding of the control circuitry running those beasts now!

  • Whoever you just saved a big bunch of money should buy you a some nice resistor kits in different wattages so you don't have to parallel. You deserve that at minimum. Good methodology and great dynamic testing, many component level repair folks rely on static testing alone.

  • Saved myself the big bunch of money :winking_face: we're a tiny design studio working on creative robotics (aatb.ch) so fixing is preferred rather than costly replacement.. plus figuring/learning out how it's built is also our favorite approach so that we can best implement our various projects since we do everything ourselves and got out of art school!

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