Fluke 123B/S Service Manual - Page 125

7 Corrective Maintenance 7.5 Miscellaneous Functions 13. Check N101/31, N201/31 (TRACEROT supplied by T-ASIC N301) for the signals shown below (typical example at 20 ms/div.). +0.8V -0.8V ≈100 ms ≈5 ms If not correct check: TP432 (RAMPCLK) for 3V, 200 ns pulses. TP332 (RAMPCLK) for 0.6V, 200 ns pulses. TP331 (RSTRAMP) for +0.6V 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). These signals can also be checked at TP471 (SCLK) and TP472 (SDAT). 16. Check SMPCLK_A (D401/15) and SMPCLK_B (D451/15) for a 5 MHz (time base ≥ 10 ms/div) or 25 MHz clock signal (3.3V). Check SMPCLK (N301/38) for a 5MHz or 25 MHz clock signal of 0.6V. 17. Check TP301 (REFADCT) for +2V, and TP302 (REFADCB) for +0.45V 18. Check the ADC supply voltages +3V3ADCA (D401/28, D451/28) and +3V3ADCD (D401/2, D451/2) for +3.3V. 7.5.7 Channel A Ohms and Capacitance Measurements 1. Press and select MEASURE on A: I OHMΩ. 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 50 Ω 1) 500 µA 500 Ω 500 µA 5 kΩ 50 µA 1) 50 Ω range for CONTINUITY only. 50 kΩ 5 µA 500 kΩ 0.5 µA 5 MΩ 50 nA 30 MΩ 50 nA 7-13