Diagnostic Testing and Troubleshooting (2620A/2625A)

5

Display Assembly Troubleshooting

5-18. Display Assembly Troubleshooting

The following discussion is helpful if it has been determined that the Display Assembly is faulty. Refer to Figure 5-8 for Display PCA test points. This initial determination may not be arrived at easily, since an improperly operating display may be the result of a hardware or software problem that is not a direct functional part of the Display Assembly. Consult the General Troubleshooting Procedures found earlier in this section for procedures to isolate the fault to the Display Assembly. Use the following discussion of display software operation when troubleshooting problems within a known faulty Display Assembly. A Display Extender Cable (PN 867952) is available for use during troubleshooting. Note that this cable must be twisted to mate correctly to the connectors on Display and Main PCAs.

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 problems involving individual display segments. When either of the special display patterns is selected, the beeper is also sounded for testing without interaction with the Microprocessor. Table 5-8 indicates the display initialization possibilities.

A2TP4 DTEST*

1

1

0

0

 

Table 5-8. Display Initialization

 

 

 

A2TP5 LTE*

 

POWER-UP DISPLAY INITIALIZATION

 

 

 

1

 

All Segments OFF

0

 

All Segments ON (default)

1

 

Display Test Pattern #1

0

 

Display Test Pattern #2

 

 

 

Figure 5-9 shows the timing of communications between the Microprocessor and the Display Controller. Figures 5-10 and 5-11 show Display Test Patterns #1 and #2, respectively. Refer to the Display Assembly schematic diagram in Section 8 for information on grid and anode assignments.

DSCLK

 

 

 

 

 

 

 

 

 

DISTX

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

 

DISRX

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

 

 

CLEAR TO

 

 

 

 

 

 

HOLD OFF

CLEAR TO

 

RECEIVE

 

 

 

 

 

 

 

RECEIVE

 

26 ∝s

 

 

 

 

 

 

 

26 ∝s

 

 

 

 

 

 

 

 

 

s40f.eps

Figure 5-9. Display Controller to Microprocessor Signals

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Fluke 2625A, 2635A service manual Display Assembly Troubleshooting
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2635A, 2625A specifications

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