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Located in CNC, on Connect card.
Lower fan.
Computer power supply connector.
Power supply enable connector.
CN9 PWR SW on connect card.
Connect Card.
Short CN9 contacts together.
CN304 on 5AX card.
CN304 cable to power supply.
CN403 to front panel connect card.
CN403 & CN1 at front panel connect card.
CN1 from front panel connect card.
Locate CN1 on connect card.
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OmniTurn G4 CNC: Troubleshoot Computer Power Supply


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Upper fan off and 2CR not lit:
These instructions assume that the CNC does not power up, and that you have first done trouble-shooting here, and discovered that the upper fan is off, and 2CR is not lit.

How it works:
The motherboard turns on the computer power supply when the Control On button is pressed. The computer power supply turns on relay 2CR, which connects 110 VAC line voltage to the upper fan (and to the servo and auxiliary power supplies).

For reference, front panel wiring schematic is available here.

Possible causes:

Troubleshooting steps:

  1. Cables from power supply: To quickly determine if connections from power supply to 2CR are the problem, remove blue cover, then power up the CNC. Reach inside the computer chassis and determine if the lower fan is running. If you prefer to use a meter, check for 12 volts DC between black and yellow wires of any spare computer power supply connector. If the lower fan is working, or if you have 12 volts, the power supply, motherboard, and control on switch are probably OK, but there may be an issue with connections between the power supply and relay 2CR on the connect card. Go to "Connections From Power Supply", below.
  2. Cable from Control On switch: If the lower fan is not running, check that the power supply enable cable from "Control On" switch is connected at motherboard. Note: on some motherboards, this connector is located on back edge of motherboard instead of side.
  3. Control on switch: If the power supply enable cable is connected, the "Control On" switch might be defective.
    • Set CNC power ON.
    • Use a DC voltmeter to check voltage across the orange and red wires on the Control On switch: you should measure about 3.5VDC.
      • If you do not measure 3.5VDC across the orange and red wires, locate CN9 PWR SW connector on the connect card. Measure across the black and white wires. If you measure 3.5VDC at CN9, the issue is cable connections between connect card and control on switch. If you do not measure 3.5VDC at CN9, use tiny probes to measure across the black and clear wires on the power supply enable cable at the motherboard. If you measure 3.5VDC there, then there is a cable or connector issue between the mother board and the control on switch. If you don’t measure 3.5VDC there, then the power supply or motherboard may be bad.
      • If you get 3.5VDC at the orange and red wires, press the Control On switch button: the voltage should drop to about 0V.
        • If the 3.5VDC does not drop to 0V, the switch is bad. (p/n 995​-12​-201)
        • If the 3.5VDC drops to 0V but the lower fan does not start (and there is still not 12VDC on the spare computer power supply connector), then the power supply or motherboard may be bad. Replace the power supply first: ATX power supply, part number 995​-16​-020. If replacing the power supply does not correct the issue replace the motherboard: Motherboard complete, G4, part number 995-17-015. You can order both of these components at the same time and return the one not needed.
Connections From Power Supply: If the lower fan is running, but the upper fan is not, there could be bad connection between power supply and connect card. The 12 volts is routed from the power supply, through the 5Ax and front panel connect cards to the connect card. The following steps describe each connector:
  1. CN304 on 5AX Card: First, check the CN304 connector, located at the top of the 5AX card, on the back-side. Verify that it is securely plugged in, then use volt meter to verify 12 volts DC between black and white wires.
  2. CN304 cable at power supply: If you do not read 12 volts DC between black and white wires, verify that the CN304 cable is connected to the power supply.
  3. CN403 on 5AX card: If you read 12 volts DC between black and white wires, locate CN403 on the inside edge of the 5AX card and verify that it is securely plugged in. Unplug and replug to verify connection. The other end of this CN403 ribbon cable is connected to front panel connect card. The 12 volt line is routed from the front panel connect card via CN1. These two connectors are not easily accessible without removing the front panel, but they can be seen through opening at the side of the control.
  4. CN1 on connect card: Locate CN1 connector on the connect card and verify that it is securely plugged in. This is the last connection in the 12 volt string from the computer power supply. If the lower fan is working but you don’t have upper fan or 2CR on connect card there may be a open trace on circuit card or bad cable.