Samsung TXJ2060, Service Manual

Page: 20 / 68

For the power system of K51A chassis, all
output voltages remain the same during
stand-by. So, to reduce power consumption, it
is necessary to cut the leakage current flowing
through FBT B
+ (130V) and tuner port V
T
(33V)
during stand-by (Picture OFF).
The power consumption reduction circuit cuts
leakage current. A P-channel MOSFET is used
as a switching element.
The operating principles are as follows:
1. In stand-by, the voltage of the power control
port (micom IC) becomes low (0V). During
power ON, however, it becomes high (over
4V).
2. The voltage between S-G (Q801 P-channel
MOSFET) should be over 3.5V, so that the S-D
current (Q801) can keep flowing.
3. When the voltage of the power control port
becomes low, the current flowing through
Q903 (R812) is cut.
4. When the voltages across R803 become less
than 3.5V, the S-D current (Q801) is cut.
5. DZ809 is required for protecting the G-port
(Q801).
3-3-13 Precautions when servicing
1. Q801 can sustain a continuous flow of 11ADC.
If Q801 is destroyed, the S-D is shorted.
But, the TV functions normally and only the
power consumption during stand-by increases
(2.5W
®
6W).
2. No Picture ON : Q903 is open or DZ809 is
shorted. At this time, check both Q903 and
DZ809. If the power-consumption reduction
circuit does not work normally after checking
both Q903 and DZ809, then short the S-D
ports of Q801.
Alignment and Adjustments
3-10 Samsung Electronics
3-3-12 Power Consumption Reduction
Circuit during Stand-by (Option)
OmA
R801
FBT B+
OmA
TUNER 33V
OmA
Q903
130 RECTIFIED
DZ809
Q801
SFP9640
R812
R910
10K
POWER
CONTROL