Troubleshooting Oscilloscope Plug-Ins

A quick way of checking the vertical amplifier input of your oscilloscope is with a vertical preamplifier plug-in unit. After you’ve isolated a problem to a specific plug-in unit, a plug-in circuit board can further isolate the problem and, once you’ve traced the problem to a specific block, you may be able to pinpoint the issue with a close visual inspection. Troubleshooting can often be hastened by spotting loose leads or burned components.

Another way to speed up troubleshooting is with the substitution method, which can be used for many levels of oscilloscope troubleshooting. When servicing an oscilloscope with a plug-in module, you can isolate faulty subsystems by replacing questionable plug-ins with plug-ins you know work. If you’re troubleshooting an oscilloscope with a plug-in board, you can replace the questionable board with a functional one. You can also substitute plug-in components to quickly troubleshoot a suspect stage, but there are some rules you’ll need to follow.

First, ensure that you use the same part number when substituting components. Make sure your oscilloscope is powered off when substituting so that you don’t damage the oscilloscope or the component. Carefully remove/replace components in order to avoid physical or mechanical damage to the components. You’ll want to keep variables to a minimum, which is to say you should only substitute one component at a time and, if the new component doesn’t correct the fault, restore the original component before moving on.

While several components in a circuit will have the same part number, you must avoid component swaps within the circuit: if you fail to return the components to their original place you may have to recalibrate the entire circuit. Lastly, when components are properly replaced the circuit in your digital storage oscilloscope may require a simple performance check and spot calibration after the repair is finished. Once you successfully troubleshoot the problem return the components to their original positions in order to prevent recalibrating the whole circuit.

After completing your USB oscilloscope repair, double check that the correct replacement components were used; if the part number’s suffix is incorrect, the oscilloscope may function, but it may not calibrate correctly. In cases when you can calibrate the oscilloscope, failure or irregular operation may occur when you use your oscilloscope in the future, because another parameter of the oscilloscope might have been selected for operation.


George Leger has a Masters in Electrical Engineering from Stanford University, worked in private industry pioneering surface-mount technology and in government research labs for twenty years, published several papers on surface-mount technology, co-authored papers published in national symposiums on accelerator technology, was past president of SMTA and an adjunct professor at the community college level, holds a patent, and is a certified microchip design partner, serving as a consultant to many companies developing electronic circuits.

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