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CT-S1390Y
X-RADIATION
WARNING:1.
The potential source of X-Ray Radiation in moni
tor set is the High Voltage section and picture
tube.
2. When using a picture tube test jig for service,
make sure that the jig is capable of handling
26.0kV without causing X-Ray Radiation.
It is important to use an accurate, periodically
calibrated high voltage meter.
NOTE:
High Voltage Check
1. Set the line voltage to 120 V AC and turn the unit on after
connecting high voltage meter to the unit.
2. Select the Video Line A input and receive monoscope pattern.
3. Adjust Sub-Bright and Sub-Contrast until the picture is black.
4. Measure the High Voltage. The meter (electrostatic type)
reading should indicate 24.5kV + 1.5kV.
Ifthe meter
indication is out of tolerance, immediate service and
correction is required to prevent the possiblity
of
premature component
failure.
5. To prevent an X-Radiation possibility, it is essential to use the
specified picture tube.
Radiation Safety Circuit Test
This test must be made
as a final check before the set is
returned to the customer.
(1) Connect DC amperemeter to TPD1 (+) and TPD2 (—).
(2) Connect
Electrostatic high voltage meter between
the
CRT
anode
and
chassis
ground
for measuring
high
voltage.
(3) Set AC line to 120V/60Hz,
and apply a monoscope
pattern at the line B, adjust BRIGHT
and CONTRAST
customer
controls to obtain 700
X 100pA
indication on
DC amperemeter.
(4) Turn chassis off, and short R802 with a short jumper.
(b) Set AC line to about 80 volts, and turn chassis on.
Slowly increase the AC line voltage until the start point
of lose of H-SYNC on the picture and check that the
beam current and the high voltage is A or B in Table 1
at the point.
(6) Turn chassis off and remove a short jumper.
Table 1
MEN
Beam Current (HA)
High Voltage (kV)
400--600
not exceeding 28
EN
601—800
not exceeding 27.6
Circuit Explanation
HORIZONTAL OSCILATOR DISABLE CIRCUIT
To monitor the high voltage, the positive DC voltage from
the cathode of D531
is applied through zener diode D571
and D572 and divided by R532 and R533 to pin 49 of IC301,
which is the input terminal of the X-Ray Protection Circuit.
Under
normal
conditions,
this
voltage
is insufficient
to
activate the X-Ray Protection Circuit.
If the high voltage increase over the specified voltage, the
voltage at the pin 49 of IC301
increases
and causes
the
X-Ray
Protection
Circuit to activate.
Then
it causes
the
horizontal oscillator frequency to increase, loss of holizontal
synchronization and lowering of the high voltage.
In the process described above, the voltage at the pin 49
of IC301
is compared
with the voltage at pin 51 of IC301
which
is basically a constant voltage fed from the zener
diode D532, divided by R539 and R535.
If excessive beam
current
is drawn, the lowered voltage is fed to pin 51 of
(301 through zener diode D570 and R534 to aid operation
of the X-Radiation Protection Circuit.
R531
PING
47
R533
D571
D572
MA4051L
MA4051L
9v
р
ЕВТ
СБА
0556
MA4062L
ЧИ)
маазвон
Fig. 2
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