Adjusting inverter control in Tektronix 7104 oscilloscope power supply

Access to 109V test point

Access to 109V test point

In this short article I want to share a trick that I learned today while checking the power supply of my trusty Tektronix 7104 oscilloscope. Step A2 of calibration section of the manual calls for measuring/adjusting of pre-regulated 109V voltage on TP1326 test point. Typically, test point access for this step requires removing power supply cover which takes time and exposes high voltages. The test setup presented on a title picture( click on it to make it bigger) shows how to access this test point leaving power supply cover in place.

The power supply cover is at ground potential so don’t try to reach the test point with non-insulated probe. I used Tektronix Klip Chip IC probe threaded through nearby ventilation hole to grab the test point post. The post is clearly seen through a larger hole, through which an adjustment potentiometer R1293 is usually accessed. A flashlight is handy.

Next picture shows the closeup of the test connection. A test probe is supported by a “Third Hand” thingy – I wanted to observe voltage fluctuations in the course of two hours to make sure it stays within limits.

I’m hoping this trick will be useful for somebody dealing with similar power supply.