Channel A Ohms And Capacitance Measurements - Fluke ScopeMeter 123 Service Manual

13. Check TP258 (TRACEROT supplied by T-ASIC N301) for the signals shown below
(typical example at 20 ms/div.).
+0.8V
-0.8V
≈100 ms
If not correct check:
TP432 (RAMPCLK) for 3V, 200 ns pulses.
TP332 (RAMPCLK) for 0.6V, 200 ns pulses.
TP331 (RSTRAMP) for +3V pulses, with varying pulse with and repetition rate.
All pulses are supplied by D-ASIC-D471.
14. Check TP310 (REFATT) for alternating +1.2V and -1.2V pulses. The repetition
frequency depends on the time base, and is for example 500 ms at 20 ms/div.
15. Check the SCLK and SDAT lines for +3.3V pulse bursts (C-ASIC pin 25 and 26).
16. Check TP437 (Sample clock) for a 5 MHz (time base ≥ 10 ms/div) or 25 MHz clock
signal (3.3V).
17. Check TP301 (REFADCT) for +1.62V, and TP302 (REFADCB) for +0.12V
18. Check the ADC supply voltages VDDAA ,VDDDA, VDDBB, VDDDB, and VDD0
for+3.3V
19. Check TP401 and TP451 for 0V.

7.5.7 Channel A Ohms and Capacitance Measurements

1. Press
Connect a current meter between Input A and the COM input. Select the various
Ohms ranges, and verify that the current approximately matches the values listed in
the table below.
If not correct, the protection circuit or the current source in the T-ASIC (N301) may
be defective.
If the current is correct, and the Volt function is correct (so ADC is correct), then the
Ohms part in the C-ASIC is defective: replace N101.
Range
Current
1)
50 Ω range for CONTINUITY only.
and select
MEASURE on A:
1)
50 Ω 500 Ω
5 kΩ
500 µA 500 µA 50 µA
≈5 ms
I
OHMΩ Ω Ω Ω .
50 kΩ 500 kΩ
5 µA 0.5 µA
Corrective Maintenance
7.5 Miscellaneous Functions
5 MΩ 30 MΩ
50 nA 50 nA
7
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