Fluke 8842A Instruction Manual page 136

8842A
Instruction Manual
Check for the same waveforms at outputs U215-11 through U215-18. (However, the high
level should be approximately 30V.) If these waveforms are OK, then strobe decoder
U213 and display control U212 are OK in this regard.
6-51. 3-to-8 Strobe Decoder (U213)
Check for strobe waveforms 0-7 on U213-4, -5, -6, -7, -9, -10, -11, -12. Reference U213-
4 for STROBE ZERO. Check for strobe decoder inputs SL0, SL1, SL2 on U213-1, -2, -3
respectively.
6-52. 8-Bit Segment Driver (U217)
Check that U217-1 through U217-7 all look like the waveform DIGIT DATA. High level
is 3.8V to 4.3V.
Check that U217-12 through U217-18 all look like the waveform DIGIT DATA except
high level is approximately 30V.
6-53. 4-to-7 Segment Decoder (U216)
Check that U216-1, -2, -7 are low and U216-4, -6 and U216-9 through U216-15 look like
the DIGIT DATA waveform.
6-54. 8-Bit Digit Driver (U218)
Check that U218-1 through U218-4 all look like the waveform DIGIT DATA. High level
is 3.8V to 4.3V.
Check that U218-15 through U218-18 all look like the waveform DIGIT DATA, except
that the high level should be approximately 30V.
6-55. Hex Inverter (U203)
At this point the display should be "unfrozen" by pressing any button. The instrument
should then complete the power-up self-test and begin normal operation. Then do the
following:
1. Check that U203-9 is the same as STROBE ONE and that U203-10 is STROBE ONE
2. Check that U203-5 is the same as STROBE TWO and that U203-6 is STROBE TWO
3. Check that U203-11 shows positive pulses 50 us to 300 us while repeatedly pushing
4. Check that the waveform seen at U208-15 is the same at U203-13, -4 and inverted at
6-50
inverted.
inverted.
front panel buttons in normal mode and that U203-10 shows the inverse.
U203-3, -12.