Variations In The Display; A3 A/D Converter Pca Troubleshooting - Fluke 2640A Service Manual

8. If a segment under each of several (or all) grids fails to be turned on (or off)
properly, one of the anode drive signals may not be connected properly from A2U1
to A2DS1. When an anode signal is at Vcc, and a grid signal is at Vcc, the
corresponding segment on the display is illuminated.
9. If the Microprocessor has difficulty recognizing front-panel button presses, the
switch scanning signals SWR1 through SWR6 should be checked. When no switch
contacts are being closed, the switch scanning lines should have about 20 kΩ of
resistance between each other (through two 10 kΩ pull-up resistors to Vcc). Unless
one of the switches is closed, none of the switch scanning lines should be shorted
directly to GND at any time.

Variations in the Display

Under normal operation, the display presents various combinations of brightly and dimly
lit annunciators and digits. However, you may encounter other, random irregularities
across different areas of the display under the following circumstances:
•
After prolonged periods of displaying the same information.
•
If the display has not been used for a prolonged period.
This phenomenon can be cleared by activating the entire display and leaving it on
overnight (or at least for several hours). Use the following procedure to keep the display
fully lit:
1. With power OFF, press and hold the left arrow key, then press power ON.
2. Wait a moment for the instrument to beep, then release the key. The entire display
will now stay on until you are ready to deactivate it.
3. At the end of the activation period, press any button on the front panel; the
instrument resumes the mode in effect prior to the power interruption (Active or
Inactive.)

A3 A/D Converter PCA Troubleshooting

The following paragraphs provide troubleshooting hints for the A3 A/D Converter PCA.
Use this material in conjunction with Chapter 2, "Theory of Operation."
To avoid electric shock, disconnect all channel inputs from the
instrument before performing any troubleshooting operations.
Diagnostic Testing and Troubleshooting
WARNING
Troubleshooting the Instrument
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