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Chapter 3: Service
Troubleshooting and Repair
The frequency response of the probe is determined by the amplifier hybrid in
the probe and the probe cable. If the probe fails the bandwidth test, factory
repair is necessary. Also read "Incorrect Pulse Response" below.
Incorrect Pulse Response (flatness)
If the probe's pulse response shows a top that is not flat (incorrect ac gain), it
is most likely caused by an inaccurate 50-Ω load on the probe. The probe is
designed to work into a 50-Ω load that is accurate within 1.0% (±0.5 Ω).
Check the value of the load you are using before you suspect the probe. If the
load is accurate, the gain problem with the probe will have to be repaired by
the factory.
If the probe appears ac coupled at a high frequency, check for a loose probe
tip.
Incorrect dc Gain
The dc gain is a function of the values of internal parts. It is independent of
the load on the probe. Any failure of the accuracy of the dc gain requires
factory repair.
Incorrect Input Resistance
First, check that the probe tip is not loose. The input resistance is determined
in the amplifier hybrid in the probe and cannot be repaired in the field. The
probe must be returned to the factory for repair.
Incorrect Offset
Incorrect offset can be caused by a misadjusted offset zero (see "Offset Will
Not Zero" on the next page), lack of probe calibration with the oscilloscope, or
faulty offset drive current from the 1143A power module.
• If the probe is connected to an oscilloscope for probe power, the probe
should be calibrated with the plug-in and mainframe. See "Connecting the
Probe" in chapter 1 of this manual or the calibration information in your
oscilloscope manual. When the probe is calibrated with an 54700 series
oscilloscope, dc gain, offset zero, and offset errors should be calibrated to
specifications as long as the probe is working.
• If the probe is connected to an 1143A power module for probe power,
check the offset drive range of the power module (See, "To Troubleshoot
the Offset Circuitry" in chapter 2 of the 1143A User and Service Guide).
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