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Chapter 4: Troubleshooting
To check the backlight inverter voltages
To check the backlight inverter voltages
The backlight inverter board is accessed by opening the front chassis as described in the "Replacing
Assemblies" chapter. Below is a picture showing what the inverter board looks like (this picture is of
the back of the front chassis - the display is on the other side of this piece).
This is the backlight inverter
board
• There is an input connector at one side of the board.
• There are two output connectors on the other end of the board, that power the two backlights which
The output voltage is approximately 300-450 V
wires) when the backlight is illuminated. The voltage is approximately 1 kV before the backlight tube
is illuminated. A red LED on the backlight inverter board illuminates when the output voltage is present.
When the backlight goes off (when the oscilloscope's operating system switches to screen saver mode)
the voltage on pins 1 and 2 (with respect to ground) slowly decays to 0 V.
The outputs are controlled by the input. Notice that input pin 5 goes low to enable the output voltage.
These pins can be reached at J1 on the display board MP12.
Table 4-1
Backlight Inverter Board Input Voltages
Input Pin
#
Backlight
OFF
Backlight
ON
66
are inserted into the flat panel display.
7
6
0 V
0 V
5 V
0 V
, 40 kHz (measured differentially between the two
rms
5
4
3
2
0 V
0 V
0 V
0 V
2.5
0 V
0 V
12 V
V
1
0 V
12 V
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