Originally posted in June, 2022

The Tektronix TM50n is an “n”bay (where n = 1 to 6, the number of bays) mainframe which can host and power TM500 plug-ins. It was available in 1 through 6 bay versions and was the predecessor to the TM5000 mainframe: See my post here about the TM5000 mainframes. Tektronix themselves had dozens of plug-ins available which comprised power supplies, signal generators, oscilloscopes, multimeters, test oscillators, calibrators, attenuators, filters, logic analyzers, frequency counters, audio analyzers and more. It is important to note that while TM500 plug-ins can be used in the TM5000 mainframe, the reverse is not true: TM5000 plug-ins cannot be used in a TM500 mainframe.

Part of the repair/refresh process of any TM500 mainframe requires the use of a Power Module Tester which (in conjunction with some basic test equipment and appropriate load resistors) can check the following:

• +-33.5V dc supplies (loaded and unloaded) for voltage, current capacity, and ripple
• Pass transistors (NPN and PNP) for shorts, leakage, and gain
• 25Vac floating supply loaded and unloaded for voltage, ripple, and phase
• +12V dc supply for voltage

Tektronix used the Module Tester when mainframes needed to be checked or required service. The Tester was never sold publicly; it was built and distributed internally by Tektronix. The original design dates back to at least 1977. As originally built, it used a double-sided circuit board with point-to-point wiring connections to the front panel.

Recently, one of members of the Tekscopes newsgroup (Jared Cabot) updated the board/switch design to eliminate the point-to-point wiring and use currently available components. He also designed a custom front panel using PCB material and made the entire project available to anyone who would like to build one. Of course, I ordered the necessary parts and built one using a scrapped TM500 plug-in:

3D printed the sub-panel and drilled holes to match the front panel

I will not go into the details of using this module to test and check each compartment in a TM500 mainframe. That information is covered in the updated documentation that Jared has provided (also see link above). However, the tester has proven itself especially useful since I found a couple of weak pass transistors (tested under load) in a couple of different mainframes. After purchasing a mainframe on the used market, or after servicing a mainframe, I can now quickly check each compartment for proper voltages and functionality.