4-18
P/N 9-500-0255
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
5. Connect an Oscilloscope 10 x 1 probe to TP33 (AEC) on the Host Microprocessor board,
connect the probe ground to TP25 (AGND). Set the oscilloscope as follows:
•
Sweep Time = 10 msec per division
•
Vertical Sensitivity = 2 V per division
•
Trigger Mode = Normal, with positive-going edge trigger
6. Initiate an exposure and record the voltage at 25 msec after the trigger point on the oscil-
loscope. If the recorded voltage is between 9.2 to 9.8 VDC, the unit has passed and you
can proceed with AEC Calibration. If the unit fails, adjust the AEC Detector board resis-
tor R1 as per Section 5.2.
5.2
AEC Detect Board—R1 Adjustment
The value of the R1 currently installed on the AEC Detect board is used to calculate the
correct value for the replacement resistor. Perform the R1 resistor value calculation as
follows:
1. Note the result of the voltage check in Step 6 of Section 5.1 above.
2. Remove the AEC Detector Assembly as per Chapter 6, Section 3.4.2.
3. Set the assembly on its side with the sensor windows on the top plate facing forward.
Remove the 6 screws securing the AEC Cover to the detector assembly.
4. Remove the cover and set aside, taking care not to touch the film covering the sensors.
5. Remove the 2 screws securing the D-sub connector to the end of the AEC Detector
Assembly. Remove connector.
6. Remove the 4 screws securing the AEC Detect board to the AEC Detector Assembly.
Remove the board.
7. Measure the resistance across R1 and calculate the replacement value using the follow-
ing formula:
9.50
÷
(result noted in Step 1) x value of current R1 = replacement resistor
value
example
: 9.50
÷
11.0 VDC x 1.4 k
Ω
= 1.2 k
Ω
Note…
The replacement resistor value typically falls within the 1.0 k
Ω
to 1.7 k
Ω
range.
8. Replace R1 on the AEC Detect board with a 1/4 Watt, metal film, 1% resistor with the
value determined in Step 7 above.
9. Reverse Steps 2 through 6 to install the AEC Detector Assembly.
5.3
Initial Calibration—Large Focal Spot (Mo)
This procedure will make Gain and Offset adjustments to the automatic exposure control
system for large focal spot exposures. Exposures used to adjust the Offset must be taken
between 240 mAs and 350 mAs, and exposures used to adjust the Gain must be taken
between 40 and 80 mAs. Always take sample exposures, then adjust the amount of
attenuation to achieve the proper mAs before making Gain or Offset adjustments.
1. Go to Step 3 for units with no HTC Bucky, units with HTC Bucky, go to Step 2.
Note…
For large focal spot calibration with an HTC Bucky, the unit must be in 100
mA mode. Ensure the HTC Threshold is low enough to remain in this mode.
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