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Tandy CM-4 User Manual

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6.
High
Voltage Shut-down System
The
shut-down
circuit
prevents
the
high
voltage from
rising above a
preset
level.
Under normal
operating
conditions,
this circuit is
in-
active.
Operation
of
the
protector
circuit depends
upon
a heat-
er
pulse
which
appears at
pin
{3)
of
the horizontal out-
put
transformer
(T602).
It monitors
a
heater pulse
subjected
to
rectification by D603.
Being in
proportion
to
the
voltage of
that heater pulse,
if
the
incoming
high voltage
increases and exceeds its
limit,
the heat-
er pulse
voltage
also
increases. As
a
result,
there is
a
larger voltage
produced to
charge
C617
so
that
its
potential
will eventually
be higher
than
the
voltage
(
+ 22V) of
Zener
diode
(D605)
turning
it
ON.
With
D605
turned
ON,
the
X-ray
protector
(of
IC601
)
oper-
ates
to
stop
the
horizontal
oscillator circuit,
shutting
down the resultant
high
voltage.
FROM
PIN©
OF
T602
/ HEATER
\
\
pulse
;
>
R615
D603
-w
M—
D605
R618
^
VA-
R619?
±ZZC617
R6175
-^
77T
Figure
6. High
Voltage
Shut-Down
System
Circuit
R616
^
-AW-(V)
C607
7.
Power
Supply (Figs.
7
10)
The
entire
monitor
circuitry
is
protected
by
a
4.0A
fuse
(F701),
located
on the Main Chassis
Board (PCB-A)
that
is connected
to
the
hot side of
the
AC
line
input.
The
secondary
circuit
is
protected
by
a
1.5A
fuse
(F702),
mounted on
PCB-A.
AC
Line voltage
is applied
through
the Line
filter (L702)
to
the
power
ON-OFF
SWITCH
(SW701).
With SW701 set
in the ON position, AC
voltage
is ap-
plied
through
a
Bridge
Rectifier
circuit.
A
conventional type
Automatic Degaussing
circuit,
consisting
of
a
positive coefficient thermistor (PR701
)
in
series
with
the
degaussing coil assembly
(L701
),
is
used.
The
AC
input voltage
is rectified
by
the
Bridge
Rectifi-
er
circuit
(D701
,
D702,
D703,
D704) and then
applied
to the
Regulator
circuit.
A
switching
type
Regulator
cir-
cuit,
utilizing
a
silicon
controlled rectifier
(SCR701),
is
used to
maintain
a constant DC
voltage level
regard-
less
of
fluctuations \n the AC
input
voltage.
The negative
horizontal
pulses
that
are
produced
at
ter-
minal
@of
the
Horizontal Output
transformer
(T602)
are converted
into
a saw
tooth wave by
R713
and
C71 1 which
is
applied
to
the Phase
Detector
circuit
in
the
IC701 (Power Regulator
integrated
circuit)
via
pin
(5)
.
Output from the
Phase
Detector
circuit is
ap-
plied
internally
to
the
SCR
Drive stage
where
it is
am-
plified and
then
utilized as
the
SCR
gate
(timing)
pulse.
Gate
pulse timing is
determined by the
action
of the
Error Amplifier
stage
in
IC701
which is
controlled by
the setting of
the
+116V Adjust
control
(R707).
Filtered DC voltage
derived from the
pulses
produced
at terminals
@
and
@
of
T602
is
used to
turn
OFF
SCR701. If
the AC
input
voltage increases,
the
turn-
on time
of
SCR
701 decreases.
And
if the
AC
input
voltage decreases;
the turn-on
time
of SCR701
in-
creases.
The
+
5.
1
V,
+
1 2V
and
+
1
8V
supplies
are
produced
as
a
result
of rectification
through
D71
3
of the
pulses
developed
at
terminal @of
T602.

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Tandy CM-4 Specifications

General IconGeneral
BrandTandy
ModelCM-4
CategoryMonitor
LanguageEnglish

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