Theory of Operation
Power Supply
2
2-7
Power Supply Signals
2-7.
Table 2-3. Power Supply Signals
Signal Name
Description
BACKLIGHT_ON*
Control signal generated by U25. In Model 867B, this signal toggles the backlight
power levels.
BATT_LVL
Monitors an attenuated (0 to 5V) version of the raw battery voltage. This signal is
monitored by the U25 microprocessor A/D Converter. The attenuation factor is
0.0909:1 with an output impedance of approximately 91 k
Ω.
BATT_TYPE
Monitors an attenuation level of the battery charging voltage. The attenuation ratio is
0.0901:1 with an output impedance of approximately 91 k
Ω.
=
If the measured voltage
is greater than 11 volts, the battery is assumed to be an alkaline cell. Voltages 10.5
volts and below indicate that a Fluke BP7217 battery pack has been installed.
BATT_ELIM
This is a contact on the battery eliminator input receptacle. It is pulled to LINE with 5
k
Ω
and tied to GND4 through
=
475Ω,
=
forming a 10.51:1 divider. If open (voltage
>1.0V), a line-powered battery eliminator has been installed. If closed (shorted to
ground), the battery eliminator is not plugged-in or is not powered
.
CONTRAST
PWM signal from U25. The frequency is set at U25_SYSCLK/(CLOCK_DIVIDER x
COUNTER_LIMIT), yielding 4.8 MHz/(4 x 4096), equaling 293 Hz. The PWM signal
has 12-bit resolution, which can vary the duty cycle from 0 to 100%.
IBL+
Current source generated by power supply used to run the LCD backlight. Current
source is controlled by the BACKLIGHT_ON* control signal. Typical current level is
80 mA. This is the sourcing node derived from unregulated DC, typ6.0V
(5.8V minimum.)
IBL-
Current return for IBL+, with approximately 1V burden.
POWER_DOWN
Powers down the GMM. Signal is generated by U25. This signal shuts the GMM off
completely. Pulled-down to GND with 20 k
Ω
.
PWR_RESET*
Signal generated by the power supply when the VCC power supply drops below 3.0
volts. The reset lasts 100 milliseconds minimum. If the selector is left in the OFF
position or the GMM is powered down, the PWR-RESET* signal restarts the 100 ms
time-out period. This signal is pulled up to VCC by 10 k
Ω
.
VEE_ON
Control signal generated by U25. Turns the VEE power supply on and off. Pulled
down to ground by 100 k
Ω
.
WAKEUP*
This signal is generated by both the rotary selector switch and the WAKEUP button.
Upon going LOW, followed by a return to HIGH, the GMM powers up. In the OFF
position, this feature is overridden by the OFF switch.
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 ...