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Tektronix TM500 Power Frame Tester

Posted on June 25th, by Shaun Merrigan in Electronics, Test Equipment. Comments Off on Tektronix TM500 Power Frame Tester

Tektronix TM500 Power Frame Tester

The Tektronix TM50n is an “n”bay (where n = 1 to 6, the number of bays) power frame which can host and power TM500 plug-ins. It was available in 1 through 6 bay versions and was the predecessor to the TM5000 power frame: See my post here about the TM5000 power frames. 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 power frame, the inverse is not true: TM5000 plug-ins cannot be used in a TM500 power frame.

Part of the repair/refresh process of any TM500 power frame 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 power frames 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.

Tektronix 067-1201-99 Front Panel as originally built. Image courtesy TekWiki
Tektronix 067-1201-99 PCB and Components as originally built. Image courtesy TekWiki

Recently, one of members of the Tekscopes newsgroup (Jared Cabot) updated the board/switch design to eliminate the point-to-point wiring and use 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:

TM500 Tester Front Panel Assembly: Front Panel, sub-panel, Front Panel PCB, and Main Switch PCB

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

TM500 Module Tester 3D Printed and Drilled Front Sub-panel
TM500 Tester Assembled Main PCB
TM500 Module Tester 5v Regulator and PCB
TM500 Tester Front Panel and Switch (updated)
TM500 Module updated Front Panel and Switch Assembly: No point to point wires!
TM500 Module Tester assembled.

I will not go into the details of using this module to test and check each compartment in a TM500 power frame. 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 power frames. After purchasing a power frame on the used market, or after servicing a power frame, I can now quickly check each compartment for proper voltages and functionality.

Thanks for reading.

Shaun Merrigan

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