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8842A
Instruction Manual
6-63. Track/Hold Troubleshooting
If a problem is suspected in the Track/Hold (T/H) circuit, first check the power supply voltages of all active components. (See Table
Next, check the T/H output waveform at TP103 with an oscilloscope. Set the 8842A to the VDC function and 2V dc range, apply +1V dc across the HI and LO INPUT terminals, and trigger the scope from the falling edge of line
1.Short the HI and LO INPUT terminals, and select the 2V dc range.
2.Short
3.Connect
If the 8842A fails step 2 but not step 3, then U303 is bad. If the 8842A fails both steps 2 and 3, then the fault is in the A/D Converter or the T/H Amplifier. To tell which, lift the end of R318 closest to the front panel (connected to
6-64. Ohms Current Source Troubleshooting
Malfunctions in the ohms functions can be caused by a fault in the Precision Voltage Reference, Ohms Current Source, or Ohms Protection. Malfunctions can also be caused by a fault in the DC Scaling circuit which loads the Ohms Current Source.
First check the
To determine whether the Ohms Current Source is being loaded down by the DC Scaling circuit, select the VDC function and connect a 10 kΩ resistor between the collector of Q404 and ground (Reference Low). (Selecting the VDC function opens K401, and configures the Ohms Current Source in the 20 kΩ range.) If the voltage across the 10 kΩ resistor is 1V, then the Ohms Current Source is working (at least in the 20 kΩ range), and the problem is probably due to a defect in the DC Scaling circuit.