Tektronix TM5006 Power Frame Refresh
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.
In terms of cost, a basic 3-bay mainframe + signal generator + frequency counter + power supply would have cost USD 1240 (1972 dollars), or USD 8000 in 2021 dollars. A similar system purchased in 1995 would have cost USD 5200 (1995 dollars) or USD 9200 in 2021 dollars.
I have several of these power frames and I will document the restoration/refresh processes here.
The goal in repairing/refreshing these units is to return them to factory specifications and establish the best reliability possible. To that end I do a thorough visual inspection looking for problems, check and replace any out of specification carbon composition resistors and replace 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 test all the new capacitors I install for leakage (at rated voltage + 5%), ESR, and Q. Typically, the capacitors I use have higher voltage ratings than the ones they replace. They are always physically smaller and can be of different lead configuration so adapter boards are needed in some cases.
I also check the pass transistors for open/short condition and HFE (DC beta).
Once the suspect components are replaced and the unit has been thoroughly cleaned, it can be load tested. The factory manual has specific procedures and test fixtures for each power frame. 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 requires 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 are within specification for the TM5006. Further testing can 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 frame is ready to be put back into service.
Thanks for reading.