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Adjustments
Model 8902A
Adjustment 22-Battery
Backup
Reference
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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HP 345514
Procedure
1. Connect the voltmeter to A13TP10 (+5V). Measure and
record the dc voltage with respect
to
ground.
Voltage at A13TPlO
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.
y6
x
Voltage at A13TPlO
=
Vdc
yc,
x
Voltage at A13TP12
=
Vdc
4.
Make the following calculalation.
- 1
I
[ I '
I /
0.95
x
Lowest Voltage
of
Step 3
=
f0.05V of the voltage calculated in step
4.
Vdc
5. Connect the voltmeter to A13TP11 (VR). Adjust A13R12 (VR) until the voltmeter reads within
5-38
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