XE-50 Recorder Interface Board
Theory of Operation
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0070-10-0441
Passport 2®/Passport 2 LT™ Service Manual
2.9
XE-50 Recorder Interface Board
2.9.1
Cooling Fault
The Cooling Fault signal is driven by an FET (Q2), to the CPU to alert the CPU that a cooling
fault has occurred. A “Cooling Fan Failure” message will be displayed on the unit. The fault
can be cleared, if there is no obstruction in the fan, by cycling system power. In normal fan
operation, a pulse train is present at the SENSE pin. A missing pulse detector monitors this
pin during fan operation. A stalled, open or unconnected fan causes the TC646 to trigger its
startup timer once. If the fault persists, the FAULT output goes low, and the device is latched in
its shutdown mode. The Cooling Fault signal is also generated if there is an over-temperature
condition. That is, a temperature rise above the point where the fan's PWM control signal is
at 100%. A “Cooling Fan Failure” message will be displayed on the unit, but no action is
necessary if the temperature normalizes.
2.9.2
Fan-Fault Sense
The SENSE input (U2 pin 5) is connected to a resistor divider network (R5 & R30) to scale
down the tach pulses from the fan. During normal fan operation, a brief interruption in the
fan current generates pulses into the sense resistors network. If the device is not in Shutdown
mode, and pulses are not appearing at the SENSE input, a fault exists. The Sense Network
shall scale-down the pulses that will meet the requirements of the TC646 of 90mV minimum
at pin 5.
2.9.3
Power Filtering
Power filtering of the recorder logic 5VDC is provided by L1 together with C5 and C6. This
circuit provides a low pass filter to reduce noise introduced into the system power. Since the
load is digital logic, the current peaks are minimal. This board provides the power filtering
for the recorder motor and print head. It must suppress the high current peaks from affecting
the power supply and power distribution within the system. The suppression reduces these
peak loads to less than the recorder in-rush current with a maximum voltage ripple of
0.5VDC.
Capacitor C7 is for the purpose of reducing induced PWM switching noise. The value of this
capacitor depends on the fan current consumption. Therefore, this capacitor value may be
adjusted after lab measurements are analyzed. A provisional capacitor (C16) is included as
a placeholder with a different footprint to further aide in the elimination of the fan's
acoustical noise, if required.
2.9.4
XE-50 Interface
J4 Interfaces the XE-50 Recorder to this Module. Data is transferred serially to and from the
recorder when it gives the indication that it is ready to accept data. The signals SINEN* and
RDY* are ANDed together to produce the REC_CTS*, which is processed by the CPU for
data flow-control.
