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Replace the Output Driver U17 (G3 CNC only)

These instructions apply only to G3 CNC

Failure to actuate M03, M04, M08, M12, M13, or M25 could be caused by bad output driver U17 on MC2 board. If troubleshooting all switches, cables, connectors, etc, does not fix the problem, U17 may be the culprit.

After troubleshooting all switches, cables, and connectors associated with the M‑function that doesn't engage, you can verify that U17 may be bad by checking voltages on terminal strip TB1 in the spindle cabinet.

To make these measurments, the spindle cabinet must be open, the CNC controlled powered up, and the servos must be on.

MDI mode will be used to issue the m‑function. For all measurements, the meter must read about 12 volts DC between the two terminals before the m‑function is issued. After the m‑function is issued the meter should read 1 - 2 volts DC. If the voltage does not drop to about 1 - 2 volts when m‑function is issued, replace U17.

Refer to this list for terminals to check for each M‑function:

M03: TB1-5   to TB1-8
M04: TB1-7   to TB1-8
M08: TB1-10 to TB1-8
M12: TB1-15 to TB1-8
M13: TB1-12 to TB1-8
M25: TB1-11 to TB1-8

If the voltage doesn't drop to 1 - 2 volts, the driver on the motion card (MC2) is the probably the culprit.
Replace U17 (ULN2803A; available at DigiKey.com).

Click for MC2, MISC Cable, TB1 schematic (PDF)

Click for how to access motion card (MC2).

U17 on MC2 card

Image of U17 on MC2 card


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