Prima LC-20S3 Service Manual page 20

2. Troubleshooting guide
This series models adopt built-in power. The power to the main board may be different when the
unit adopts different panels or whether the audio amplifier is located on the main board or not. The
following is the detailed power in different cases.
Model Audio amplifier
LC-20S25 AN5277, locates on
LC-20S15 power board,
Vcc=18V
LC-15S3 TPA1517, locates on
main board, Vcc=12V
LC-23S25 AN5277, single audio
amplifier, Vcc=18V
LC-20S3 AN5277, locates on
main board, Vcc=18V
2.1 No raster, no picture and no sound
When the main power is turned on, the unit's indicator lights up in red (red indicator is controlled by
+3.3VSTANDBY), use the remote control or the unit's STANDBY to lights up the blue indicator.
Whether the IR board's
red indicator lights up?
Whether
indicator
when
STANDBY button?
Whether
backlight lights up?
Whether Whether the backlight
power or PBIAS pin is
backlight power or
PBIAS pin is normal
Check power circuit or whether the
VCT4993I PBIAS signal is normal
Power
number
main board
X401
8 pin
X401
6 pin
X401
X702
N
Y
the blue
lights up
N
press the
Y
Y
the
N
the
Y
l
N
socket
Pins
on the
PWM: backlight brightness control
signal.)
1, 2: +12V
6: GND;
1, 2: GND
5: PBIAS
1, 2, 3: +20V;
7: STANDBY
1,2: +12V
7,8: GND
Power board's +3.3V
is abnormal
Confirm the IR
sensor and its power
supply is normal
Whether the voltage
of the panel is
normal?
Backlight board damage or protection.
Replace the backlight board
18
(PBIAS: backlight
3, 4: GND 5: +3.4V
7: PBIAS
3, 4: +12V
6: PWM
4, 5, 6: GND
8: +3.3V
3, 4: GND
9: PBIAS
Indicator damages or blue
Y
indicator +5V
abnormal (check +5V circuit)
Y
MST519 is abnormal without
signal output or the output
signal is abnormal
ENABLE,
8: PWM
5,6: +18V
10: PWM
power is