Troubleshooting The Power Supply; A2 Display Pca Troubleshooting - Fluke 2640A Service Manual

Troubleshooting the Power Supply

To troubleshoot the power supply circuits, check the test points for each voltage,
proceeding from the raw dc supply through the 5V switcher and subsequent regulator
circuits. If one of the supplies is folded back due to excessive current draw, unplug the
ribbon cable at A3J10 on the A3 A/D Converter PCA to see if this unloads the power
supply. If this works, then troubleshoot the A3 A/D Converter PCA. When tracking
down power supply loads, use a sensitive voltmeter and look for resistive drops across
filter chokes, low value decoupling resistors, and circuit traces. Also check for devices
that are too warm. On the A3 A/D Converter PCA, all devices run cool except A3U5
microprocessor and A3U8 FPGA, which run warm, but not hot.

A2 Display PCA Troubleshooting

The following provides troubleshooting hints for the A2 Display PCA. Use this material
in conjunction with Chapter 2, "Theory of Operation." A Display Extender Cable is
available from Fluke (PN 867952) for use during troubleshooting.
To avoid electric shock, disconnect all channel inputs from the
instrument before performing any troubleshooting operations.
The Display Controller reads the DTEST* and LTE* inputs to determine how to
initialize the display memory. DTEST* and LTE* default to logic 1 and logic 0,
respectively, to cause all display segments to be initialized to "on". DTEST* is
connected to test points A2TP4, and LTE* is connected to A2TP5. Either test point can
be jumpered to VCC (A2TP6) or GND (A2TP3) to select other display initialization
patterns. Display Test Patterns #1 and #2 are a mixture of "on" and "off" segments with a
recognizable pattern to aid in troubleshooting. When either of the special display
patterns is selected, the beeper is also sounded for testing without interaction with the
Microprocessor. Table 5-13 indicates the display initialization possibilities.
A2TP4 DTEST*
1
1
0
0
Figures 5-1 and 5-2 show Display Test Patterns #1 and #2, respectively. Refer to the
Display Assembly schematic diagram in Chapter 7 for grid/anode assignments.
REVIEW
Table 5-13. A2 Display PCA Initialization Routines
A2TP5 LTE*
1
0
1
0
REM SCAN SET FUNC
mV
x1 k
Figure 5-1. Display Test Pattern #1
Diagnostic Testing and Troubleshooting
WARNING
Power-Up Display Initialization
All segments OFF
All segments ON (default)
Display Test Pattern #1
Display Test Pattern #2
Ω
1
Troubleshooting the Instrument
5-27.
5-28.
EXT TR
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