Replace U17 Driver IC On MC2 In G3 OmniTurn CNC Lathe

These instructions apply only to G3 CNC, or G2 w/MC2

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:
(12V SO is to verify servos on and meter good)

12V SO: TB1-9 to TB1-812V SO Test

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

If the voltage doesn't drop to 1 - 2 volts, the driver on the motion card (MC2) is the probably the culprit.

*For M12 & M13, write program with eight M12's or M13's (one M12 or M13 is a 1/2 second pulse, so eight will keep function on for four seconds).

Click for MC2, MISC Cable, TB1 schematic

Click for how to access motion card (MC2).

Remove U17 by slipping a small screwdriver under one end of the IC, then the other, alternately lifting each end of the IC by a small amount so as not to bend the leads.
Replacement U17 (ULN2803A) is available at DigiKey.com).

When installing the new one, be sure you orient it correctly. Pin 1, which is marked by either a dot or a half-circle depression in the plastic case of the chip, goes down (toward the gold connector).
Be sure all the pins on the chip are well aligned with the socket when you push it in, making sure that no pins get bent under the body of the chip. It's easy to bend them but hard to straighten them without breaking them off.

Replace the Output Driver U17 (G3 CNC only)