HP 8901B Operation And Calibration Manual page 428

Model 8901B Adjustments
Adjustment 22
BATTERY BACKUP
Service Sheet
24
Description
The battery backup circuit switches the supply for the internal RAM
to
an internal battery when
either the +12V or +5V supply drops. The two supplies are measured on the memory assembly and
the voltage
at
which the backup switches is adjusted
to
a level based on the measured supply voltages.
Equipment
Digital Voltmeter
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H P 3455A
Procedure
1. Connect the voltmeter to A13TPlO (+5V). Measure and record the dc voltage with respect to
ground.
Voltage at Al3TPlO Vdc
2. Connect the voltmeter to A13TP12 (+12V). Measure and record the dc voltage with respect to
ground.
Voltage at A13TP12
Vdc
3. Make the following calculations.
2/5 x
Voltage at Al3TPlO =
x
Voltage at A13TP12 =
Vdc
Vdc
4. Make the following calculation.
0.95
x
Lowest Voltage of Step 3 = Vdc
5. Connect the voltmeter to A13TP11 (VR). Adjust A13R12 (VR) until the voltmeter reads within
~t0.05V of the voltage calculated in step 4.
Adjustment
22 5-37