Fluke ScopeMeter 123 Service Manual page 120

123
Service Manual
2. Press
3. Apply a 1 kHz square wave to Input A and Input B, and change the test tool
4. Check TP154 (ADC-A) and TP254 (ADC-B) for the signal shown below:
5. Check TP156 (TRIGA) and TP256 (TRIGB). The TRIGA and TRIGB signals must
6. Check the supply voltages +3V3A (+3.3V), -3V3A (-3.3V), and +5VA (+5V).
7. Check TP151 (POS-A) and TP251 (POS-B) for about +1.1V (trace at mid-screen),
8. Check TP152 (OFFSET-A) and TP252 (OFFSET-B) for about +1.1V.
9. Check TP303 (REFN) for -1.2V.
10. Check TP153 (DACTESTA) and TP253 (DACTESTB) for 0V. If TP153 is +1.7V,
11. Check TP155 (MIDADCA) and TP255 (MIDADCB) for about +0.9V.
12. Press
7-12
to open the
SCOPE INPUTS
Press to open the
I
SCOPE MODE: ROLL MODE | WAVEFORM MODE:
sensitivity (V/div) to make the complete square wave visible.
Input positive.
Input zero.
Input negative
A trace amplitude of 1 division results in an 150 mV voltage on TP154/255
Moving the trace position, with a zero input signal, results in a TP154/254 voltage of
about +0.3V (bottom) to +1.4V (top).
If the voltages are not correct, do steps 6 to 16; if these steps are correct, then replace
the C-ASIC.
If the voltages are correct, the error is most probably caused by the ADC, or ADC
control: continue at step 16.
be the inverted input signals, with an amplitude of 50 mV per division trace
amplitude.
Moving the trace position, with a zero input signal, results in a TP156/256 voltage of
about +0.4V (bottom) to -0.4V (top).
If the voltages are not correct, do steps 6 to 16; if these steps are correct, then replace
the C-ASIC.
If not correct trace to the Fly Back converter on the Power part.
+0.4V (trace at top of screen), +1.8V (trace at bottom of screen).
If not correct check the PWM circuit (in the Digital Circuit).
the C-ASIC is in the reset state (200 mV/div fixed sensitivity); check SDAT and
SCLK, see step 15.
to open the
SCOPE INPUTS
Press to open the
I
SCOPE MODE: NORMAL | WAVEFORM MODE:
Select a time base of 20 ms/div.
menu.
menu, and select:
SCOPE OPTIONS ...
0.3 to 1.4V
menu.
menu, and select:
SCOPE OPTIONS ...
I
NORMAL.
}
150 mV/div
I
NORMAL.