Thursday, January 12, 2017

Samsung Plasma Television – How to troubleshooting Y sustain board – Y buffer board

Y Board Configuration
“Y” PCB configurations will vary depending on screen size. The replaceable buffer PCB style will be separate.Y Main and one piece upper and lower buffer PCB. The non replaceable buffer styles will require the Y Main to be replaced in the event the buffer circuit fails.
Y Board Circuit
This Y Main board maintains the sustain voltage waveform, the initialize waveform and generates the Y rising/falling ramp waveforms. The wave shape that is output to the respective Y electrodes varies depending on luminance levels and whether that pixel is actually selected. Y board failures usually cause the entire panel to be dark. Y board failures can sometimes be verified by visual inspection of the IC and FETs.The Y board operates similarly to the X board with some variations. The Y board output signal is opposite in polarity to the X Board signal. The Y Board signal is specific for each pixel. Pixels that are off do not receive a signal. Pixel brightness is controlled by varying the number of sustain pulses. Because the Y board signal is more detailed than the X board signal is output to a pair of multiplexing boards. The upper and lower Y buffers divide the screen in half vertically. The Y Buffer Boards apply the address waveform to the Y terminals of the panel. The Y Board signal varies depending on the input video. Each Y electrode gets a unique signal; this means that the Y signal is applied through an upper and lower buffer board.
The Y Main is responsible for the Address pulse to determine which sub pixel will be used.
The Y main is responsible for lighting the selected sub pixel to a specific illumination by using the sustain pulses.
Y Board Sustain Pulse
Only the X and Y boards are responsible for the sustain pulses. As the number of pulses increase to the individule sub-pixels, the brightness and color saturation increases as well
The Y Main is responsible to initialize or erase the charge from the sub pixel and prime it for use again.
Y Board Troubleshooting
The Y board is responsible for the address, sustain and initialize functions. Y board failures can cause the entire panel to be off. This is because the Y electrodes are not being addressed properly. Y board failures can sometimes be verified by visual inspection of the IC and FETs. Additionally inspect the green fusible resistors looking for a brown or burned component. Y board failures are much more common than X board failures. A shorted component on the Y board may load down the Vs, Vset and Vscan voltages. If the Vset is low or missing the panel will not initialize creating image retention. If the Vscan voltage is low the pixels cannot be selected creating a black screen. And finally if the Vs voltage is missing or low the panel cannot be sustained creating a dark picture. If the Vs, Vset or Vscan voltages are low or missing verify the Y board is not loading down the line. Measure the resistance of Vs, Vscan and Vset connections reference to circuit ground. A dead short or low resistance on any of these connections is an indication of a shorted component. Another symptom is a picture defect running horizontally across the screen. This is because the Y electrodes run across the screen. A bar or picture defective that is localized to the top or bottom of the screen.
To troubleshoot the Y board verify the positive Vs voltage, the negative Vs voltage and the Vsc voltage. The voltage should match the value printed on the panel.
If any of the voltages are low or missing, unplug the Y board to see if the Y board is loading down the power supply.
Another test procedure is to unplug the unit and measure the resistance of Vsc, +Vs and –Vs SMPS inputs referenced to ground, Low or zero resistance indicates a shorted FET.
As with the X board, the fast switching and high current requirements can cause the FET’s to explode or crack, visual inspection can often show this type of damage
Y Board Failure Examples
Notice how each error contains a horizontal line
These examples show Y board errors, because the Y electrodes run horizontally, errors can often be seen across the screen.
Another Y board error can be an entirely black screen.
The Y Buffer Board time shares the Y drive signal to all the Y electrodes. Y buffer failures can cause horizontal line errors or in some cases the entire panel to stay dark.
On older style Plasma TV’s the upper and lower buffer can be replaced separately. With the introduction of a one piece buffer both upper and lower are replaced as an assembly. In the case of the Y Main with built in buffer circuits, the entire Y Main is replaced.
Y Buffer Connection Errors
If the connection from the Y buffer board to the panel is not installed properly the panel might show thin parallel lines. This is NOT a panel or a board error .
The connection between the buffer and the panel can cause these types of problems. The connections can be cleaned and reseated but make sure the power is removed before attempting.