Wednesday, January 11, 2017

Samsung plasma TV – Plasma TV Power supply Troubleshooting tips – Plasma television repair and service

SMPS
The SMPS power supply will vary slightly depending on the screen size. Both however will function identically.
Power supply removal requires the tech to remove either 6 or 8 screws be removed depending on the model and size of screen. After replacement of the SMPS make sure the voltages are adjusted according to the label posted on the panel.
The power supply provides switched and unswitched voltages for operation. The unswitched voltages are present as long as the unit is plugged into the wall. The +5VDC supply operates the main CPU on the digital board. The +33VDC supply is used by the tuner.
The other voltages are used by the panel drive circuits creating the Va,Vs,Vset and Ve voltages.
The Power Factor Control (PFC) circuit is used to save energy. Taking advantage of the capacitive effect of the pixel elements allows the power supply to operate at a reduced duty cycle. Using a large inductor and the capacitive effect of the panel allows energy to be stored and accessed as needed.
A separate transformer supplies the +5VDC Stand-By B+ to the Digital board. This voltage powers the Microprocessor (IC201) and enables the Key Matrix and the Remote IR Sensor. This turns on the relay activating the rest of the Power Supply PCB. If this supply is missing or low the unit will not turn on. If this signal is not present check the supply voltage for the micro.
Power Supply Troubleshooting
If the Ve voltage is low or missing disconnect the power supply cable from the X board. If the Ve voltage rises the X board is probably shorted. If the voltage stays low the SMPS board needs to be replaced. If the Vs voltage is low or missing it can be caused by a defective X or Y board. Check both boards for short circuits before replacing the SMPS board. If the Vs voltage is too high an effect called diffusion may occur. Diffusion is when the initialize voltage is too high. Excessive voltage causes unwanted pixel firing creating intermittent sub-pixel flashes. Power on-off cycling can be caused by a shorted component on the Logic board loading down the standby 5V.
Power Supply Failure Examples
One possible symptom is defects in the video such as herringbone noise
# Other symptoms would be similar to X or Y board failures as the SMPS board provides the power to these boards
# Before replacing an X or Y board be sure the Vs, Vsc and VE voltages are being provided by the SMPS board.
If the Ve voltage is low or missing disconnect the power supply cable from the X board. If the Ve voltage rises the X board is probably shorted. If the voltage stays low the SMPS board needs to be replaced. If the Vs voltage is low or missing it can be caused by a defective X or Y board. Check both boards for short circuits before replacing the SMPS board. If the Vs voltage is too high an effect called diffusion may occur. Diffusion is when the initialize voltage is too high. Excessive voltage causes unwanted pixel firing creating intermittent sub-pixel flashes. Power on-off cycling can be caused by a shorted component on the Logic board loading down the standby 5V
Power Supply Adjustments
Each plasma panel has a unique voltage setting required to display a picture properly and maintain long life. Incorrect adjustment of the power supply can create picture errors. Whenever a power supply board is replaced the new board must be adjusted to match the panel values shown on the sticker.
If a power supply board is replaced it is imperative that the new power supply be adjusted to match the existing panel settings. Incorrect adjustment can cause the picture to be too dark or too bright. Extreme misadjustment can greatly reduce panel life.
Locations of the test points and adjustments on a typical SMPS power supply. These adjustments must be performed when the SMPS or the panel is replaced.
Protection Circuits
Over Voltage Protection
The Power Supply PCB has an Over Voltage Protection circuit as well as a regulator circuit. It is designed so that when an Over Voltage condition occurs in any part of the power supply it does not affect another output stage. The following table shows the Over Voltage specifications. The unit must be unplugged to reset this error.
Intermittent shutdown may be caused by an over-voltage condition.
Item
Over Voltage Point
D3.3VDC
4.7VDC
D6VDC
8.2VDC
VA (typically 75VDC)
94VDC
Over Current Protection
If a short circuit occurs on either the VS, VA, 12V, 6V or 3.3V lines, the SMPS stops operating, but should not fail. When the short circuit is removed from the source line, the Power Supply will operate normally again.
Power Supply Diffusion
The diffusion problem can be seen using the sweeping test pattern located in the customer menu under the burn protection selection. Diffusion is caused by a power supply that is not properly matched to the panel.
Over diffusion is the most common symptom, this is where the SMPS is providing to much Vs voltage for the panel.
SMPS adjustments to eliminate the diffusion problem.
Allow the unit to warm up 15 to 20 minutes to stabilize the SMPS Operation
# Access the Customer Setup Menu, then Screen burn protection, then Signal Pattern
# Adjust the Vs voltage while monitoring the screen. Adjust the Vs voltage up or down, if the diffusion error is not diminished as the voltage change approaches 10 volts the panel needs to be replaced
# Do not adjust the Vs voltage more than 15VDC from
the value printed on the panel label.