6-85
NOTE
POSITION GAIN
is
not an iterative calibration as the gain
is
directly calculated.
Position Gain is calculated at 50 mV per division only, using the stored Position Offset calibration con-
stant. The DAC counts corresponding to +4 divisions of Position Offset are added to the Position
Offset constant and an acquisition is made. After storing the results, a corresponding -4 division
acquisition is made, and the two values of acquisition memory are checked for eight divisions of
change in the calibration limits. The Position Gain constant is then calculated as a result of the data
taken and stored as a Position Gain calibration constant. A Position Gain constant more than 20%
different from the nominally expected value will cause the test to fail.
Testing Method:
Preamplifier Position Gain A1OU420and A1OU320(schematic diagram 9):8200
POSITION
GAIN
6. Swap Peak Detector hybrids between channels to see if the problem channel reverses. If so,
replace the faulty Peak Detector.
5. If the Preamp hybrid itself is suspected of being defective and the other channel is fully functional,
swap Preamp hybrids between channels to see if the problem moves to the other channel. If so,
replace the defective Preamp. If not, check the hybrid mount connections of the defective channel
for corrosion or contamination that may be causing a poor contact.
4. Check that the bypassing components in series with the power supplies are not open. Also check
that the dc bias voltages at the Preamp are approximately the levels indicated on the schematic
diagram in the service manual.
3. Use the SPECIAL menu choice of CAL PATH ON to determine whether the offset error is prior to
the Peak Detectors or after. Troubleshoot in the appropriate direction to locate the source of the
offset error.
2. Use the FORCE DAC test to determine if the CH1-PA-POS and/or CH2-PA-POS voltages are
being controlled by the DAC System. If not, troubleshoot the DAC System.
1. Check that the decoupling network, R420/C423 or R222/C222 is functional.
Troubleshooting Procedure (refer to test 8000 for more information):
The Position Offset is then calculated by acquiring a ground level signal and comparing the Acquisition
Memory value to what a ground acquisition should be (center screen is OOh).If the value is not within
1/2 DL for calibration or 1 DL for diagnostics, the position DAC outputs (CH1-PA-POS and/or CH2-
PA-POS) are adjusted to compensate. When the acquisition is within limits, the test result is set to
PASS. If the position offset cannot be adjusted to within specification, the acquisition count for an
abort is taken, and the test result is set to FAIL.
Position Offset is calculated at 50 mV per division only. Position offset must be performed for all four
acquisition modes to compensate for the common-mode offsets in the CCD arrays that are not
corrected by CCD centering. After the hardware is set up and the CCD constants set for the particular
mode of operation, the Preamplifier is balanced by executing the balance routine, but only changing the
DAC settings-not the cal constants. This assures an accurate position measurement.
Testing Method:
Acquisition System Position Offset:8100
POSITION
OFFSET
Table 6-6 (cont)
Maintenance-2430 Service
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