Fbt Protection Circuit Operation Check; High Voltage Limiter Circuit; Side Pin Distortion Coarse Adjustment - Hitachi 35UX85B/CZ68 Service Manual

Adjustment Procedure
(1) Connect a 10kfi resistor between Q945 base and GND
and check that the picture disappears.
(2) Disconnect resistor immediately and the power cord.
(3) Discharge C905 as follows.
_L
2 (wire wound resistor)
= '=
2.2.2 +26V Audio Power Supply
Preparation for Adjustment
(1) CONTRAST to maximum, BRIGHTNESS to center.
Adjustment Procedure
(1) Connect a 10kfi resistor between Q963 base and GND
and check that the picture disappears.
(2) Disconnect resistor immediately and the power cord.
(3) Discharge C905 as foltows.
2.2.3 +12V Power Supply
Preparation for Adjustment
(1) CONTRAST to maximum, BRIGHTNESS to center,
Adjustment Procedure
(1) Connect a 1 OkM resistor between Q964 base and GND
and check that the picture disappears.
(2) Disconnect resistor immediately and the power cord.
(3) Discharge C905 as follows.
z (wire wound resistor)
=
2.2.4 +B Over Voltage
Preparation for Adjustment
(1) CONTRAST to maximum, BRIGHTNESS to center,
Adjustment Procedure
(1) Connect a 1Ofi resistor to both ends of R955 and
check that the +B voltage goes up and down.
2.3 FBT Protection Circuit Operation Check
Preparation for Adjustment
(1) Turn on the power of the set.
Adjustment Procedure
(1) Add lOK!Z! (1/16w-1/8w) resistor between Q713 base
and GND (/ENH2/ connector pin 0) and check the
operation.
(2) After checking, remove AC PLUG and the IOK resistor
to return the set to the previous state.
After about 15 seconds, discharge C906. Turn on the
power again, and check the set operates normally.
2.4 High Voltage Limiter Circuit Operation Check
Checking Preparation
(1)
Connect the assembly to a standard set.
(2) Connect a high voltage voltmeter between CPT anode
terminal (anode cap side) and the ground.
(3) Set AC input voltage to 120f3V.
(4) Receive a circle pattern or color bar signal and set
"BRIGHTNESS" and "CONTRAST" to maximum. Adjust
screen VR so that beam current is I&O. 1 mA. (The
voltage of ABL terminal -C741 both ends should be
12V or less.)
Adjustment Procedure
(5)
Check that the normal high voltage and +B voltage is
as below.
CHASSIS E HT
IB
+B
II
El
CPT
Adjustment Preparation
(6)
Set AC input voltage to 120?3V. Then, connect the
VR(lOOK-B) and Rl(27K) to R927 and ground side as
below.
Note: At that time the value of VR should be maximum.
Use a voltmeter of input impedance IOM ohm or
more with indication to the 1 st decimal place.
Adjustment Procedure
(7) Keep CONTRAST, BRIGHTNESS, and Screen VR as in
Item (4). Reduce the VR value gradually, and check
that the picture disappears when high voltage is El.
Immediately after checking that it disappears, turn off
the set switch. Remove the VR and high voltage
voltmeter. When connecting or removing high voltage
voltmeter to or from anode cap, be sure to turn off the
switch of the set. Also, be sure to perform it after the
chassis discharge or residual high voltage, because
the high voltage of CPT anode may be left.
2.5 Side Pin Distortion Coarse Adjustment
Adjustment Preparation
(1) Receive a circle pattern signal or cross-hatch signal.
(2) Set the AC input power supply to 120+1V.
(3)
For picture controls, set the BRIGHTNESS to center
and set the other controls to their standard conditions.
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