867B,863
Service Manual
2-10
Boost Preregulator (B)
2-13.
The boost preregulator o15 volts from an input of +12 volts from the battery
eliminator or 5.5 to 10 volts from the battery.
U27 provides this boost in conjunction with L1, CR20, and C3. If U27 is not functioning,
the voltage at the positive of C3 is approximately 0.4 volts below the voltage on C90.
R114 provides peak current limiting to prevent rapid burnout of the boost circuit in the
event of an overload. Since R114 requires a functional U27, it does not provide complete
protection. R12 and R73 set the output voltage, while the other discrete components
provide timing and compensation for the regulator.
The output of this stage is delivered to the NiCd battery charger (C) and to the DC-DC
converter (D). R125 allows the charger and boost circuit to be tested independently of
the rest of the GMM. R125 is especially useful if a large load causes <15 volts at the
cathode of CR20.
Battery Charger (C)
2-14.
The battery charger consists of the following two sections:
•
Q22 and its associated components provide a linear current source of either 170 mA
or 40 mA to charge the NiCd battery. Transistors Q1, Q2, Q3, Q6, and Q11 provide
logic control of the charger state.
•
The other part of the circuit is U32 and its associated components, which provide a
timeout of at least 16 hours to prevent continuous overcharging of the battery. This
circuit is reset each time a battery eliminator is plugged in (via U34, R141, R140
and C91).
A full charge of approximately 170 mA can only be provided to the battery if Q1, Q2,
and Q6 are turned on, Q3 is off, and Q11 is off. These states correspond to the GMM
being connected to line but turned off and U32 not being timed out. U32 is inhibited
from advancing by CR5 when power is on.
VR1 prevents Q2 from turning on until the battery voltage rises above about 5.8 volts.
This prevents excessive power dissipation in Q22 with a dead battery or shorted cells.
Note
The Fluke battery pack (BP7217) uses an extra wire to allow charging
current to flow. If individual batteries are installed, no connection is made,
and no charging current can flow.
Summary of Contents for 863
Page 49: ...Maintenance Disassembly 3 3 5 OFF 1 6 Places 4 5 5 3 3 2 os5f eps Figure 3 1 Disassembly ...
Page 50: ...867B 863 Service Manual 3 6 os6f eps Figure 3 1 Disassembly cont ...
Page 52: ...867B 863 Service Manual 3 8 5 1 6 2 3 4 os30f eps Figure 3 2 Reassembly ...
Page 96: ...6 1 Chapter 6 Schematic Diagrams Title Page 6 1 A1 Main PCA Assembly 6 3 ...
Page 98: ...867B 863 Service Manual 6 4 FLUKE 867 1001 Sheet 2 of 5 Figure 6 1 A1 Main PCA cont ...
Page 99: ...Schematic Diagrams 6 6 5 FLUKE 867 1001 Sheet 3 of 5 Figure 6 1 A1 Main PCA cont ...
Page 100: ...867B 863 Service Manual 6 6 FLUKE 867 1001 Sheet 4 of 5 Figure 6 1 A1 Main PCA cont ...
Page 101: ...Schematic Diagrams 6 6 7 FLUKE 867 1001 Sheet 5 of 5 Figure 6 1 A1 Main PCA cont ...
