CM151
3-1
CA - SERVICING
HIGH VOLTAGE AND X-RADIATION PROTECTION
A potential source of x-rays is the picture tube, if the
high voltage (HV) is out of specification . When the HV
is operating properly, there is no x-radiation . For the
CA chassis family, the HV has no adjustments . A HV
shutdown circuit is used to prevent excessive HV and
x-ray emissions.
THEORY OF OPERATION (SHUTDOWN CIRCUIT)
This circuit basically monitors the sweep pulse voltage
derived from the sweep transformer TX3204 pins 5 & 6.
This voltage is rectified, and applied to a 12V zener
diode ZDX3004. When the HV reaches its maximum
allowed ,value (see drawing) the zener diode conducts,
the voltage on pin 29 of the video processor (ICX2200)
increases until it reaches the threshold voltage of 3.5
VDC, and shuts down the TV
If the shutdown circuit has operated, the
microcontroller will prevent the TV from being turned
on again, without first having to unplug the AC cord to
reset the microcontroller.
SERVICING
SECTION 3
TIP:
Make a momentary short between the OUTPUT and
GND of the IC6002 (RESET CIRCUIT) this will reset the
microcontroller IC6000.
Apply signal through the video generator or tune the
TV color receiver to crosshatch pattern. Connect an
accurate HV meter between the picture tube anode and
chassis ground. Access Video Menu and adjust
Brightness and Contrast controls for minimum screen
luminance . Wait until, the Video Menu or display
disappear. Read HV meter.
SCREEN
B+ VDC
HV NOM HV MAX
SIZE
(0 BEAM)
KV
KV
25
124.0 +/- 2%
28
29
27
124.0 +/- 2%
27
29
32
128.5 +/- 2%
30
31.5
36
128.5 +/- 2%
30
31.5
MODULE LEVEL REPAIR ONLY
COMPONENT LEVEL REPAIR
CA CHASSIS
SHUT DOWN CIRCUIT
Video Processor
ICX2200
RL2
RIN
P29
C
GND
ZDX3004
DX3005
RL1
