Power Supply And Protection - Sony KDL-26S3000 Training Manual

Chapter 1 - Features and Circuit Descriptions
Protection
would be no diagnostics indication from the power LED.
Several circuits on the WAX3 chassis are utilized to monitor voltage and
current conditions. Should a problem develop in any of these monitored
circuits the unit will shut down in most cases and blink the power LED red
in varying sets of sequences in order indicate what is likely causing the
failure. Protect circuits are located on the power supply, BU1 board and
the back light inverters.

Power Supply and Protection

3 different power supplies are used in the WAX3 chassis and these are
shown in Figures 1-8, 1-9, and 1-10. The 26" units use a G1D board, the
32" a G1H board and the 40/46" models use the G3 board. The G1D and
G1H boards are very similar in design with current capacity being their
primary difference and the presence of a PFC circuit on the G1H while
one is not used on the G1D. They both generate 24VDC to supply the
inverter circuits on the panel.
The G3 board uses the PFC circuit to directly drive the D1 and D2 inverter
boards for the 40 and 46" panels. All 3 power supplies contain over-
voltage, under-voltage and over-current monitoring. The D3 power supply
contains additiona circuits to monitor the temperature of the PFC switching
transistors and the in-rush current limit resistor R6009 as shown in figure
1-10. If either of these circuits is activated the power supply will be turned
off. The Main Micro located on the BU1 board monitors the regulated 12
volt line generated by all 3 boards. If this voltage is no longer generated
the Main Micro will flash the power LED in sequences of 2 assuming the
standby power supply is still operating.
In figure 1-9, note the PFC detection line consisting of PH6301 and Q6403
which is unique to the 40/46" models. If the PFC circuit were to cease
operating the DC voltage, which is normally around 390 volts, would drop
to less than half (rectified AC only). This would put a strain on the D1 and
D2 boards since they would attempt to keep the lamps lit but would require
extra current due to the drastic voltage drop. In this event Q6403 will pull
the control signal (which is normally high) low, turning off the inverter(s).
The symptom would be a unit that has no backlights operating but there
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