HP 8901B

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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HP 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