LG 50PG20 Series, Руководство по обучению

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Plasma Spring 2009 50PG20
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Power Supply Generic Troubleshooting Tips Power Supply Generic Troubleshooting Tips
Understanding the Power On Sequence when Troubleshooting a possible Power Supply Failure will
simplify the process of isolating which circuit board failed to operate properly. In this Section we will
investigate the Power on Sequence and examine ways to locate quickly where the failure occurred.
Check the Power On LED for Operation. A Red LED indicates a presence of 5V STB and AC-ON/DETECT.
Failure of the Power ON LED to light is an indication of loss of 5V STB or AC ON/ Detect remember the 5V STB
and AC-ON/DETECT are developed on the SMPS and sent to the Main Board.
Listen for Relay Click, the click of the Relay is an indication of RL-ON going high. RL-ON is sent from the
Main Board to the SMPS and when present the U701 controls the Relay Operation. RL-ON going High and
no Relay is a failure of the SMPS, RL-ON staying low is a failure of the Main Board.
Relay Operation means that the SMPS if working properly will output the 16V Supply to the Main Board.
This voltage will allow the Tuner, Audio and Video Circuits on the Main Board to function, and if connected to an
Antenna Input, Audio would be present. If the Relays closed and these supplies failed suspect a problem with the SMPS.
The next step of operation calls for the M5V_ON line from the Main Board to the SMPS to go high on P803 pin 21. A high
on the M5V_ON Line activates the 5V VCC line. Loss of 5V VCC results in no “Raster”, no Display Panel Reset, no Y, Z,
Control or X Board operation. Loss of 5V VCC and M5V_ON going high could be caused by any of these boards or
failure of the SMPS. M5V_ON staying low indicates a problem on the Main Board.
Remember if a voltage is missing check for proper resistance before proceeding
VS-ON is the last step of the Power Sequence and is responsible for bringing the VS and VA Voltages up.
The VS-ON signal pin 20 P803 is sent from the Main Board to the SMPS as a high, VS and VA and full operation of the
Display Panel are now enabled. Loss of VS-ON results in loss of VA and VS and no Raster, no Panel Display Reset
but Audio would be present. If VS-ON went high and VS and VA where missing the problem could be caused
by a failure on the SMPS or a circuit using these voltages. A Resistance check should narrow the possible
failures quickly.