Power Circuit - Fluke 43B Service Manual

43B
Service Manual
This prevents that at each next acquisition the trace is sampled at the same time
positions, and that the displayed trace misses samples at some places on the LCD.
The D-ASIC supplies control data and display data to the LCD module. The LCD
module is connected to the main board via connector X453. It consists of the LCD, LCD
drivers, and a fluorescent back light lamp. As the module is not repairable, no detailed
description and diagrams are provided. The back light supply voltage is generated by the
back light converter on the POWER part.
The keys of the keyboard are arranged in a matrix. The D-ASIC drives the rows and
scans the matrix. The contact pads on the keyboard foil are connected to the main board
via connector X452. The ON-OFF key is not included in the matrix, but is sensed by a
logic circuit in the D-ASIC, that is active even when the test tool is turned off.
Via the PROBE-A and PROBE-B lines, connected to the Input 1 and Input 2 banana
shielding, the D-ASIC can detect if a probe is connected.
The D-ASIC sends commands to the C-ASICs and T-ASIC via the SCLK and SDAT
serial control lines, e.g. to select the required trigger source.
Various I/O lines are provided, e.g. to control the BUZZER and the Slow-ADC (via the
SADC bus).

3.2.4 Power Circuit

The test tool can be powered via the power adapter, or by the battery pack.
If the power adapter is connected, it powers the test tool and charges the battery via the
CHARGER-CONVERTER circuit. The battery charge current is sensed by sense
resistor Rs (signal IBAT). It is controlled by changing the output current of the
CHARGER-CONVERTER (control signal CHAGATE).
If no power adapter is connected, the battery pack supplies the VBAT voltage. The
VBAT voltage powers the P-ASIC, and is also supplied to the FLY BACK
CONVERTER (switched mode power supply).
If the test tool is turned on, the FLY BACK CONVERTER generates supply voltages for
various test tool circuits.
The +3V3GAR supply voltage powers the D-ASIC, RAM and ROM. If the test tool is
turned off, the battery supplies the +3V3GAR voltage via transistor V569. This
transistor is controlled by the P-ASIC. So when the test tool is turned off, the D-ASIC
can still control the battery charging process (CHARCURR signal), the real time clock,
the on/off key, and the serial RS232 interface (to turn the test tool on).
To monitor and control the battery charging process, the P-ASIC senses and buffers
battery signals as temperature (TEMP), voltage (BATVOLT), current (IBAT).
Via the SLOW ADC various analog signals can be measured by the D-ASIC. Involved
signals are: battery voltage (BATVOLT), battery type (IDENT), battery temperature
(TEMP), battery current (BATCUR) LCD temperature (LCDTEMP, from LCD unit),
and 3 test output pins of the C-ASIC's, and the T-ASIC (DACTEST). The signals are
used for control and test purposes.
The BACK LIGHT CONVERTER generates the 400V ! supply voltage for the LCD
fluorescent back light lamp. If the lamp is defective a 1.5 kV voltage can be present for
0.2 second maximum. The brightness is controlled by the BACKBRIG signal supplied
by the D-ASIC.
Serial communication with a PC or printer is possible via the RS232 optically isolated
interface. The P-ASIC buffers the received data line (RXDA) and supplies the buffered
data (RXD) to the D-ASIC. The transmit data line TXD is directly connected to the
D-ASIC.
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