Mindray Passport 5-Lead, Руководство по обслуживанию

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Passport 5-Lead, 5L, LT, XG Service Manual 0070-00-0420 2 - 55
Theory of Operation Block Diagrams
On the secondary side, CR9 and C1 and C2 rectify and filter the 12 volt output. Likewise
CR10 and C3 rectify and filter the -23.5 volt output. L3, L4 and C4 provide additional
filtering. R1 and C5 damp energy in the 12 volt secondary leakage inductance. Likewise R2
and C6 damp energy in the -23.5 volt secondary leakage inductance. U3, R12 and R13
make up a linear regulator for the -23.5 volt output (input to the regulator is typically about 3
volts higher than the output). Q3, R14, Q4, R16 and R15 are used to gate power into the
linear regulator via a 5 volt logic control signal.
R11 senses the current in the 12 volt secondary. R17,C19,R8,R19, and C20 filter this signal
prior to sense by comparitor U2B. The 5 volt reference of U1, R8 and R19 offset the input of
the comparitor such that it will trip at approx. 1.9 amps. CR8 and C21 add hystersis and a
“hiccup” time constant to the comparitor. U2A buffers the output of U2B prior to resetting the
soft start circuit R24 and C23. Q2 functions as a follower which buffers the soft start RC prior
to pulling down the output of the pwm error amp (U1-1).
2.2.7 Planar EL Panel Board
Overview
The panel board locates physically the visible indicators in reference to the front panel of the
monitor. It contains the LED driving circuits and buffers for the EL data lines. Due to its
location in the assembly, it provides convenient means for interconnection between the CPU
board, the EL panel, the DC/DC converter, the front panel keyboard, and the speaker.
Functional Description
The LEDs provide two indicating functions: power on - green, alarm on - red.
When activated, the alarm LED is flashing at a 3 Hz rate and 50% duty cycle. The speaker
produces all the required tones (i.e. heart rate beeps, alarm and alert tones). The alarm LED
control and the speaker signals are generated on the CPU board.
A 40 lead ribbon cable from the CPU brings the required voltages and logic signals for the
EL panel, the indicators and the keyboard. Four lines control and provide data for the EL
panel. Eight output and four input lines interconnect the 8 by 4 keyboard matrix. Detailed
description of the signals and power leads is given in Chapter 3 on page 3. The DC/DC
converter generates the power for the EL panel.