Sony KV-32HS500 Training Manual page 24

Standby 5V Power Supply
Reference Figure 3-6 during the following circuit description:
The Standby Power Supply (located on the A-board) is operational as long as the set is plugged into an AC outlet.
AC power is applied to T502 through fuse FH501, and chokes L510 and L511. T502 couples the AC across to
D503 rectifier block and filter capacitor C507 (AC is also coupled to Q503 this is part of the power-on switching
circuit which will be discussed next).
The Standby 5V power supply is a simple conventional full-wave (only two diodes in D503 are used) rectifier
circuit. The resulting DC voltage (13V) is applied to the input pin of IC501 (5V regulator), which then supplies
regulated 5V to the following components:
•
IC2300 System Control (M-board)
•
IC2302 NVM (M-board)
•
IC2305 3.3V Regulator (M-board)
•
Q2312 Remote Input Buffer
•
HA/HC boards (Key Input, LED, and Remote Sensor)
Power-ON Switching Circuit
Reference Figure 3-6 during the following circuit description:
In the Standby mode, System Control (IC2300) is partially powered (using STBY 5V and 3.3V), and waiting for an
ON command from either the Front Panel Controls (IC2300/pins 93 and 94) or the Remote Control (IC2300/pin
7) (circuit not shown).
Once the ON command is received, IC2300/pin 69 (AC_RLY) outputs a high, which is applied to the base of
Q6503, turning Q6503 ON. This completes the ground path for the AC Relay (RY6701) and for the base circuit
of Q503.
Q503 turns on and supplies the initial kick voltage and current through D508 to RY6701, closing the relay switch
and supplying AC power to the Main Power Supply through Inrush resistor R6705 and D6702. Once C513 in the
base circuit charges completely Q503 turns off; D508 reverse biases and D509 forward biases, supplying a hold
voltage (9V) to keep the relay switch closed in the ON mode.
At this point the Main Power supply is turning ON (operation will be discussed next). The initial AC power to the
Main Power Supply is through Inrush resistor R6705, which limits the high surge current that occurs momentarily
at turn ON. Once the secondary voltage UNREG 11V is developed on T6703 in the Main Power Supply, it is fed
back to the Inrush Relay (RY6702). RY6702 turns on and bypasses R6705 in the ON mode. R6705 is only in
the circuit during initial power-up of the set.
Troubleshooting Tip:
Obviously, if a failure occurs in the 5V Standby Power Supply the unit will not even attempt to turn ON. If this
condition occurs, check the following components:
1) FH501
2) 13V at IC501 Input Pin (I). If missing, suspect T502, D503, and/or C507
3) 5V at IC501 Output Pin (O). If missing, suspect a defective IC501.
4) NOTE: Q503 is used as a current source for the AC relay (RY6701). If the collector/emitter
junction of Q503 becomes an Open circuit, the set will still turn ON (using voltage through D509)
and function properly with sufficient AC power input. If the AC power input is weak (Low Voltage
~90VAC), the unit will have difficulty turning ON without Q503 functioning properly.
3. Power Supply (DA-4 & DA-4X Chassis)
22