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Adjustment Procedures
5–20
AM700 Audio Measurement Set Service Manual
LCD Driver Board Adjustment (for LCD flat panel display)
The following adjustment steps set up the offset and gain for the red, green, and
blue analog to digital converters; and adjust the brightness level of the LCD
panel backlighting.
The following test equipment is needed:
H Test oscilloscope with probes
H Adjustment tool
1. On the LCD Driver board, set the Offset potentiometers, R37, R39 and R41,
to fully clockwise (CW). (Note: these adjustment may be absent from your
circuit board.)
2. Center the settings all the Gain potentiometers (R6, R7 and R9).
3. Center the BRT potentiometer (R24).
4. Disconnect the cable from J8 (VGA cable).
5. Turn on the AM700. The AM700 initializes and starts the FFT application.
1. Set the test oscilloscope
Vert Mode CH 1 On
CH 1 Volts/Div 1 V
CH 1 Input Coupling DC
A Sec/Div 400 ns
A Trig Mode Auto Lvl
A Trig Source CH 1
Slope + (plus)
Vertical Position Trace on center horizontal graticule
2. Touch View Setup in the FFT application.
3. Touch Spectrogram in the View Types choices.
4. Touch Accept Changes
5. Connect the oscilloscope probe tip to the MSB of the Red ADC at TP6. See
Figure 5–5 for test point and adjustment locations.
6. Adjust the Red Gain potentiometer, R6, until the trace goes high with pulse
trains.
7. Back off the adjustment of R6 to the point the trace stays at a constant low
level. (Voltage at TP2 will be ≈ +1.4 V).
Test Equipment Needed
Preparation for the LCD
Driver Adjustments
Adjust ADC Gain