Troubleshooting sampling scopes

Sampling scopes are quite different from regular analog scopes. When something is wrong with a sampling scope, the instrument is often completely unusable, which makes repairing it more difficult. Following these steps can make the repair process more manageable. These step apply to Tektronix modular sampling scopes such as the 661, 567, and the other 560-series scopes fitted with sampling vertical and horizontal plug-ins.

First, make sure the power supply is working properly. Power up the scope with the plug-ins installed and check all of the power supply voltages for DC voltage and for ripple. If there is ripple, there is a good chance that the power supply electrolytic capacitors need replacing. You can attach another equivalent in parallel with the suspect capacitor. If that fixes the ripple, replace the capacitor. If not, there are other problems. Don't connect capacitors while the scope is on. Be careful of polarity an voltage ratings. Be safe and think before turning on the power. When all of the power supply voltages meet the DC voltage and ripple specifications given in the manual, this first step is complete.

The second step is to get the timing (horizontal) unit working. The best technique here is to apply a pulse train waveform to the external trigger input of the timing unit while observing its output on a second oscilloscope.