OEC 9800C-Arm, Service Manual

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Calibration
mA Null Adjustments
Note : When you boot the system for the first time after replacing the High Voltage Supply Regulator, the system may display
MA ON IN ERROR . This is a fatal message that shuts the system down. This may happen because the mA Null
adjustment described next needs to be done. The proper time to adjust the offsets is just after precharge completes
because no kV control voltage is applied before precharge, and the mA readings from the sensors are not valid.
Note : The system will display the MA ON IN ERROR message one more time after you perform the following adjustments.
This is because software reads the sensors before they are correctly nulled.
Note : It is critical that you adjust the voltages at TP39 and TP40 as closely as possible to 0.00 VDC. Any error greater than 5
millivolts is a failure that necessitates replacement of the High Voltage Supply Regulator PCB.
1. Configure the C-Arm to provide 40 kVp @ .20 mA.
2. Connect a digital voltmeter between TP39 on the HVSR (LO_MA_SEN) and TP44 (LO_MA_ SEN_REF).
3. Adjust R138 for 0.00 VDC + 1.5 millivolts.
4. Connect the digital voltmeter between TP40 (HI_MA_SEN) and TP49 (HI_MA_SEN_REF).
5. Adjust R126 for 0.00 VDC + 1.5 millivolts.
PWM Chip Sync Adjustment
CAUTION : Do not make an X-ray exposure at this point in the procedure.
1. Connect channel 1 of the oscilloscope to TP79 (HF_SYNC) and channel 2 to TP57 (RAMP). Trigger the oscilloscope on
channel 1.
2. Adjust R139 clockwise until the two signals come out of sync with each other as shown in the next illustration. Note the
position of the pot.
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Service Periodic Maintenance Contents Schematics Illustrated Parts Installation