LCD DV
32LH30
27
Spring 2009
Power Supply (SMPS) PWB Operational Troubleshooting
Power Supply (SMPS) PWB Operational Troubleshooting
Power Supply Troubleshooting
Ac voltage is supplied to the Power Supply at Connector SC100. This set does not use AC Detect.
The AC input generates a Hot Ground primary power supply that runs in two states, Stand-By (168) and
Run (380V) measured at Fuse F501. This primary voltage develops all other voltages that are output
from the power supply. During Stand-By, the 5 Volt Standby should be present at connector P201, Pins
7,8,9 or 10. If Missing remove AC Power and unplug Connector P201, apply AC Power and recheck for
presence of 5 Volt Standby. Loss of 5 Volt Standby would be a Power Supply Failure. Presence of 5 Volt
Standby would be an indication of a failure on the Main Board or possibly the Front PWB (IR) assembly.
Suspect a possible short circuit loading the supply.
Remember to observe the Front Power Indicating
LED this may save some time. A lit LED indicates the Stand-By 5V voltage is present!
The Main Board sends two commands to the Power Supply Board one being PWR the other is INV ON.
These two voltages are used to control the power on turn on sequence. First via PWR (Pin 2) also known
as POWER ON, activates the Ballast voltage 24V and the 17 Volt and 12 Volt lines to the Main board. The
2
nd
command is INV ON (P201 pin 20). It is the Lamp Lighting Command Signal.
If either command (PWR-ON or INV-ON) is missing it will result in a no picture symptom, as the backlights
will not turn on.
These voltages can easily be checked with the volt meter! Remove AC Power, unplug the Connector to the
Ballast P203. Reapply AC Power and press the ON-OFF Button on either the Remote Control or Power
Button on the Unit. Watch for the Power ON LED to change color from red to blue. This is an indication the
PWR Signal was created on the the Main board. Check P700 or P201 pin 2 for the PWR-ON command
(4.9V) to the Power Supply. Check P201 for 24V (Pins 17 or 18) and 12V (Pins 13 or 14). Confirm Pin 20 of
P201 went to 3.3V. This is the INV ON signal needed to light the Lamps.
Problems with either voltage can be easily solved by following the simple steps on the next page.
