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4.7.3 Servo Controlled Oxygen Troubleshooting Tips

4.7.3.1 Check Supply Valves

Power up unit in service mode. Select Servo O2 on second page. Be sure O2 is connected. Open V1. You should

hear gas ow. Close V1, open V2. You should hear gas ow. Close V2, gas ow should stop.

If both valves are not opening, test the fuses and supply valves. Disconnect J83 at the Servo O2 board. Measure

the resistance on harness pin 1 to pin 2. It should be the supply valve resistance (50 to 100 ohms). If not, the

fuse is opened or the supply valve is defective. Repeat for the second supply valve with pins 3 to 4. If the valves

check OK, the Servo O2 board is defective.

NOTE: With one supply valve open the ow rate should me be a minimum of 35 L/min. With both supply valves

open, the minimum ow rate should be 40 L/min. If the ow rate is low, check that the regulator inlet screen is

not occluded.

4.7.3.2 Check Calibration Valve/Calibration Fan

The calibration valve is located beneath the chassis in the sensor housing. The calibration fan is mounted in

the sensor housing next to the calibration valve. Power up unit in service mode. Select Servo O2 on second

page. Open VC. This should open the calibrate valve and turn on the calibration fan. Verify the calibration fan

is running. If the fan is running then the Servo O2 board is OK and the calibration valve may be defective. If

the fan is not running check the control signal from the Servo O2 board to verify voltage is present when VC is

opened to determine if the fan or board is defective.

4.7.3.3 Check Cooling Fan

The cooling fan is mounted to the sensor housing door on the chassis cover. Power up unit in service mode.

Select Servo O2 on second page. The cooling fan should be running.

If fan is not running verify 10.0 - 13.2 Volts at J86-1 to J86-2. If voltage is present the fan is defective. If voltage

is not present the Servo O2 board is defective. Open VC, you should hear a click and the cooling fan should

stop. If the fan does not stop the Servo O2 board is defective.

Chapter 4: Troubleshooting

GE Giraffe Service Manual

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