Power Failure Circuit - Sanyo DP50741 Service Manual

Internal sub_CPU on main IC 5500 is programmed so the
set will go to standby mode when there is circuit failure as
described below. (Refer to"Block Diagram Power Lines".)
This unit is equipped with a Power Failure Detector function
included in the sub_CPU which checks for an abnormal
condition in the chassis power supplies.
If, while the power is on, a failure is caused by any of the fol-
lowing that results in a low voltage supply, the sub_CPU will
turn the unit off in 1.5 seconds to prevent further damage:
•
Failure within the power supply circuits.
•
A short circuit in the load side from the supply.
Power Failure: Detected voltage failure for circuit.
(Connected to IC5500 pin W7.)
(Normal: High; Failure: Low)
If, while the power is off, the power is switched on and any
of these failures remains uncorrected, the sub_CPU will
shut off the power within three seconds.
Power Board

POWER FAILURE CIRCUIT

IC5500
K8B
1 Power On
AA5
Check the following if the unit is turned off by the power
failure detector.
1. Disconnect the AC power cord (120V AC line) for a short
time.
2. Connect a DC Voltmeter to the circuits shown below.
3. Press the Power key and check for the proper voltage
supplies.
4. If any of these voltages is low, the power failure detec-
tor should turn the unit off within three seconds.
5. Check all circuits shown below.
Note: If power failure is detected 3 times in 15 minutes,
the set will enter the standby mode and cannot be
switched On.To reset the operating programs of the
sub_CPU it is necessary to disconnect the AC cord
for a short time.
Main
Power Fail
W7
– 5 –
D1641
D1621
T_Con Pow
D1668
Audio Pow
12V
D6702
3.3V
9V
5V