Y Board Configuration
“Y” PCB configurations will vary depending on screen size. The
replaceable buffer PCB style will be separately. 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 individual 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.
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
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.
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.
UPPER AND LOWER Y BUFFER BOARD ERROR
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.
