Troubleshooting The Lcd Display Module - Fluke 39 Service Manual

39/41B
Service Manual

5-11. Troubleshooting the LCD Display Module

To isolate a problem when the LCD display appears dead, do the following:
1. First, verify that the display module is properly connected to the main circuit board.
2. Verify that the CS_LCD, and the LCD_E signals from U3 are correct. If the timing
A0-A15, DS*, PS*, X/Y*
3. If the signals CS_LCD and LCD_E are not correct, verify that they are produced
Vertical lines across the LCD screen will most likely be due to a misalignment of the
LCD glass with its elastomeric connector. Replace the LCD display module to fix this
problem.
To isolate a problem where the LCD display contrast does not adjust correctly, proceed
as follows:
1. Press the arrow keys to verify that when entering contrast, the WIPER on the
5-12
Make certain that the flex cable is not twisted or at an angle as it enters the molex
connector of either the LCD module or the main circuit board.
is correct, the problem may be with the contrast. If there are no connection problems,
the timing waveforms are correct, and the contrast adjustment is not the problem
(see "Starting with a Dead Tester" on page 1-3), there may be a problem with the
LCD module.
0 ns
CLOCK
6.20 Min/Max
15 Min/Max
10
CS_BOOTROM
Min
41 Min/
67 Max
5.05 Min/Max
5.05 Min/Max
AD
DATA
correctly by U3. When attempting to read and write to the display, the observed
timing should match the LCD timing diagrams. If the inputs to U3 (A15, A14, A5,
A4, RD, WR, XY, PS) are all present, there may be a problem with U3.
EEPOT (U8-5) can be moved between the top wiper voltage (U8-3) of ≈3.3V and the
bottom wiper voltage (U8-6) of ≈0V. The right arrow moves the wiper toward the
top wiper voltage or increases the contrast, and the left arrow moves the wiper
toward the bottom wiper position or decreases the contrast. The newly selected value
of contrast does not get saved unless you specifically exit the contrast feature by
pressing C. For example, if the Tester is in the contrast mode and you turn the
power off, the contrast setting will not be saved as the new contrast of the display. If
moving the WIPER through its range of values does not change the contrast of the
display, there may be a problem with the analog contrast circuit or a problem with
the LCD module.
100 ns 200 ns
210.52 Min/Max
Address Bus, DS, PS, XY
150 Min
130 Min
232.84 Min/Max
229.34 Min/Max
300 ns
15 Min/Max
15 Min/Max
0
0 Min/90 Max
t21i.eps