Originally posted in June 2021
The Tektronix TM5006 is a 6-Bay power module which can host and power either TM5000 or TM500 plug-ins .
Tektronix themselves had about 130 different plug-ins available which comprised power supplies, signal generators, oscilloscopes, multimeters, test oscillators, calibrators, attenuators, filters, logic analyzers, frequency counters, audio analyzers and more. In addition, numerous third parties made plug-ins for the system. The total number of different plug-ins numbered at least 200. The system was introduced in 1972 and was available in some form through at least 1995. The system is remarkably interesting from a technology standpoint because it encompasses the move from discrete transistor circuitry in early equipment, evolving through microprocessor-controlled units in later equipment. The more modern TM5000 equipment also had network interface (GPIB) capability for control and data acquisition.
This post documents the restoration/refresh process as applicable to many of these modules.
The goal in repairing/refreshing these units was to return them to factory specifications and establish the best reliability possible. To that end I performed a thorough visual inspection, checked and replaced any out of specification carbon composition resistors and replaced any suspect electrolytic capacitors. Since the electrolytic capacitors must be removed from the circuit for valid leakage and ESR testing, that usually means replacing all of them with high quality modern equivalents. I tested all the new capacitors I installed for leakage (at rated voltage + 5%), ESR, and Q and D (Dissipation Factor). Typically, the capacitors I used had higher voltage ratings than the ones they replaced. They were always physically smaller and could be of different lead configuration so adapter boards were needed in some cases.
I also checked the pass transistors for open/short condition and HFE (DC beta).
Once the suspect components were replaced and the unit was thoroughly cleaned, it was load tested. The factory manual has specific procedures and test fixtures for each power module. The test/calibration procedure calls for fully loading each of the supply rails and checking for correct voltage regulation and ripple on the output. This required building a test jig consisting of various values of high wattage, low ohm resistors mounted on a large heatsink. As of this writing I am working on constructing this test jig. In the meantime, I used my electronic load to test each supply rail at least 6A DC:
- 8.2-volt rail: 8.109 volts at 12 A 25mV ripple
- 26-volt rail: 24.200 volts at 6A, 25mV ripple
- -26-volt rail: -24.030 volts at 6A, 25mV ripple
These results were within specification for the TM5006. Further testing could be done on each compartment using a special load tester; I am looking at a couple of options for this as well. However, for the moment, this TM5006 power module was put back into service.