Fluke 8842a instruction manual Input Voltage, Voltage AT TP801, Voltage AT TP802

8842A

Instruction Manual

f6-20.wmf

Figure 6-20. Option -09 Service Position

If the signal at the input to U801A (pin 5) is incorrect, U804 may be defective, or the switch codes may be wrong. If the latter problem is suspected, refer to Table 6-28 and test the control lines to U804 (U804-1, 8, 9, 16). If a logic error is found, it may be due to excessive loading or a faulty data latch (U803), or other cabling or main-board digital problems. High-frequency oscillation problems are usually caused by switches being on when they should be off, resulting in positive feedback loops being closed around portions of the scaling circuitry.

Table 6-27. AC Signal Tracing

RANGE

200mV

2V

20V

200V

700V

INPUT VOLTAGE (1

kHz)

100mV

1V

10V

10V

100V

VOLTAGE AT TP801

20mV

200mV

2V

20mV

200mV

VOLTAGE AT TP802

1V

1V 1V

100mV

100mV

If the signal at TP802 is incorrect, but U801-5 is OK, the digitally controlled filter section (U801A and U808) is probably defective.

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