Fluke ScopeMeter 123 Service Manual page 36

123
Service Manual
As described in Section 3.2.5, the test tool operating mode depends on the connected
power source.
The voltage VBAT is supplied either by the power adapter via V506/L501, or by the
battery pack. It powers a part of the P-ASIC via R503 to pin 60 (VBATSUP). If the test
tool is off, the Fly Back Converter is off, and VBAT powers the D-ASIC via transistor
V569 (+3V3GAR). This +3V3GAR voltage is controlled and sensed by the P-ASIC. If it
is NOT OK (<3.05V), the output VGARVAL (pin 64) is low. The VGARVAL line is
connected to the D-ASIC, and if the line is low, the D-ASIC is inactive: the test tool is in
the Idle mode. A low VGARVAL line operates as a reset for the D-ASIC.
If VGARVAL is high (+3V3GAR > 3.05V), the D-ASIC becomes active, and the Off
mode is entered. The D-ASIC monitors the P-ASIC output pin 12 MAINVAL, and the
test tool ON/OFF status. By pressing the ON/OFF key, a bit in the D-ASIC, indicating
the test tool ON/OFF status is toggled. If neither a correct power adapter voltage is
supplied (MAINVAL is low), or the test tool is turned on, the Off mode will be
maintained.
If a correct power adapter voltage is supplied (MAINVAL high), or if the test tool is
turned on, the mask software starts up. The mask software checks if valid instrument
software is present. If not, e.g. no instrument firmware is loaded, the mask software will
keep running, and the test tool is not operative: the test tool is in the Mask active state.
For test purposes the mask active mode can also be entered by pressing the ^ and > key
when the test tool is turned on.
If valid software is present, one of the three modes Operational, Operational &
Charge or Charge will become active. The Charger/Converter circuit is active in the
Operational & Charge and in the Charge mode. The Fly back converter is active in the
Operational and in the Operational & Charge mode.
Charger/Converter (See Also Figure 3-3.)
The power adapter powers the Charge Control circuit in the P-ASIC via an internal linear
regulator. The power adapter voltage is applied to R501. The Charger/Converter circuit
controls the battery charge current. If a charged battery pack is installed, VBAT is
approximately +4.8V. If no battery pack is installed, VBAT is approximately +15V.
The voltage VBAT is supplied to the battery pack, to the P-ASIC, to the Fly Back
Converter, and to transistor V569. The FET control signal CHAGATE is a 100 kHz
square wave voltage with a variable duty cycle , supplied by the P-ASIC Control circuit.
The duty cycle determines the amount of energy loaded into L501/C503. By controlling
the voltage VBAT, the battery charge current can be controlled. The various test tool
circuits are supplied by the Fly Back Converter, and/or V569.
Required power adapter voltage
The P-ASIC supplies a current to reference resistor R516 (VADALOW pin 8). It
compares the voltage on R516 to the power adapter voltage VADAPTER on pin 20
(supplied via R502, and attenuated in the P-ASIC). If the power adapter voltage is below
10V, the P-ASIC output pin 12, and the line MAINVAL, are low. This signal on pin 12
is also supplied to the P-ASIC internal control circuit, which then makes the CHAGATE
signal high. As a result FET V506 becomes non-conductive, and the Charger/Converter
is off.
Battery charge current control
The actual charge current is sensed via resistors R504-R506-507, and filter R509-C509,
on pin 9 of the P-ASIC (IBATP). The sense voltage is supplied to the control circuit.
The required charge current information is supplied by the D-ASIC via the CHARCUR
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