Ac Input And Switching B; Overview; Ac Input; B+ Rectifier - Sony TVP-08 Training Manual

AC Input and Switching B+

Overview

The AC Input and Switching B+ circuit is used to filter the AC line voltage
and generate the DC voltage necessaary to run the switching supply.

AC Input

AC enters the G board at CN6004 when the unit is plugged in. It then
passes through F6001 and L6001 and L6002 Line Filters. L6002/3 is
the High side of the AC line and splits off to two places. It is used to
power the Standby +5V supply and is connected to one of the contacts
of RY6001 Power Relay.
There are a few protection components in place in addition to F6001
Fuse. There are two spark gaps across the AC line at CN6004 AC Input.
There is also one across the AC line after F6001 Fuse. Two capacitors,
C6001 and C6002, are present on either side of L6001 Line Filter. VD6001
is a VDR across the L6002/1 and 3 for spike protection.
Troubleshooting
Problems in this area are usually the result of line spikes or lightning. If
you have a dead set and suspect lightning damage, you should remove
the G board by removing one screw and pulling it out. A quick visual
check can be performed by looking on both sides of the board for burnt
traces or components. If F6001 is open, be sure to check for any burnt
components. If everything looks OK, then check the voltage across
VD6001. If the line voltage is not present there, continue to work your
way back checking across the AC line until you find an open component.
9

B+ Rectifier

When power is turned ON, the AC line voltage is applied across D602
Bridge Rectifier because RY6001 Power Relay is closed. D602/3 + out-
puts 130 volts which is filtered by C6008, C6010 and L6003. This volt-
age is used as the B+ for the switching power supply converter circuit
and is fused by F6002. D602/4 is connected to ground through R6010
In-Rush Current Limiter at initial power ON. When the secondary sup-
plies begin to run, RY6002 will be closed which connects D602/4 - to Hot
ground.
Switching B+ Low Voltage Protect
Both outputs of the D602 Bridge Rectifier are monitored to cause shut-
down of the set. D602/3 + has a sample voltage sent to the Soft Start
circuit to monitor for under voltage. If the voltage at this point is too low,
the Soft Start circuit will raise the frequency of the switching supply, thereby
lowering the secondary output voltages and disabling regulation. The
lowering of the secondary voltages will also cause RY6002 to open or
may shut the set down. Due to the fact that the power supply voltages
will be lowered, the set will indicate an AKB shutdown by flashing the
Timer LED five times, pausing, and then repeating. This action will be
discussed in greater detail in the Soft Start section.
In-Rush Current Limiter Protect
D602/4 is monitored to ensure that the R6010 In-Rush Current Limiter
has been switched out of the circuit by RY6002. If it has not, a voltage
will be developed across it that is rectified and sent to the base of Q6004
AC Protect. If Q6004 AC Protect is turned on, IC6003 Oscillator will be
shut down. This will cause no output from the switching supply. Keep in
mind that there will be 150 volts present at F6002 since the power relay
is still turned ON. In addition, the Timer LED will flash twice, pause and
repeat. You will not be able to shut the set OFF using the remote or the
front panel switch. The set will have to be unplugged to attempt to re-
start the set.