Chapter 5: Troubleshooting
To check the backlight inverter voltages
84
To check the backlight inverter voltages
The backlight inverter board A5 is located in the front-left corner of the oscilloscope (as you face
the front panel).
• 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 are inserted into the flat panel display.
The output voltage is approximately 300-450 V
rms
, 40 kHz (measured differentially between the
two 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 A11.
Table 5-11
Backlight Inverter Board Input Voltages
Input Pin # 7 65432 1
Backlight OFF0 V 0 V0 V0 V0 V0 V0 V
Backlight ON 5 V 0 V 2.5 V 0 V 0 V 12 V 12 V
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