RADIOMETER TCM3 - Page 78

2. TCM3
TCM3 and TCM30 Service Manual
Power Supply PCB, Continued
Current
Limiter
This
function
is
performed
by
the
mono-stable
multi-vibrator
QA1c
and
QA1d.
If
and Battery
Control
DC Regulators
Serial Data
Circuit
Analog Output
Circuit
on 901-644
Analog Output
Circuit
on 901-832
the
instantaneous
current
in
Q1
exceeds
a
certain
value,
QA
Ic
will
be
triggered,
causing
QA1d,
pin
13
and
the
drive
signal
for
Ol
to
go
low.
To
prevent
any
adverse
regulator
effects
the
integral
regulator
is
reset
by
CR3
and
R31.
If the battery cassette voltage (+Vbat) drops to below 6 volts, the output of QA1
goes low and the generator signal is disabled.
Three integrated DC regulators QA50O (+5 V), QA52 (+8 V) and QA53
(-5 V), provide the power supply of the communication part. 」
The serial output signal can be measured at TP 1. It passes via Q51 and Q53. The
unloaded output at terminal 11 has an amplitude of 22 V (-14 to +8).
For test purposes, the monitor is fitted with a serial input terminal (14).
This description refers to TCM3 below RUN 22.
The control signal for the analog outputs is a pulse-width modulated square-wave
using the same input terminal (TP1) as the serial data TX signal.
Terminals 12 and 13 are short-circuited and the Flip-Flop QDS1 is released (pin 6
low). The pO, and pCO, pulses alternate, and the FF “directs” the pO, pulses to
QD50 pin 1 and the pCO, pulses to pin 13. The FF output is monitored by the
microcomputer via Q52.
The
signals are demodulated in two active low pass filters.
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Example of pulse width modulated signal for the analog outputs. TP 1.
This description refers to TCM3 of RUN 22 onwards and TCM30.
The control signal for the analog outputs is a pulse-width modulated square-wave
using the same input terminal (TP1) as the serial data TX signal.
Terminals 15 and 13 are short-circuited and the counter QD51 is released (pin 15
low). The pulses for the 4 analog outputs alternate, and the counter “directs” the
pulses to the filter in question.
The counter output is monitored by the microcomputer via Q54 and Q52.
The signals are demodulated in 4 active low pass filters.
Continued on next page