Tektronix TM500 Tester

This module is for testing all TM500 mainframes, it plugs into any slot in the mainframe. I have several TM506, and a TM504, all of which need testing, to verify voltages at the slot edge connector pins, transistors working properly, etc.. I have not seen such a tester on Ebay in over a year that i have been looking, so i decided it had to make one.

This one checks for transistor collector and emitter shorts to chassis, transistor go/no-go for dc operation, checks all five power supplies at no load and various loads (not the max loads). Click on the images to open a new tab with a much bigger pic.

The perfboard jig i assembled is laying in a blank module that Tektronix produced for people to prototype stuff in. I, instead, used a separate piece of cheap perfboard, saving the very rare and pricey original Tektronix board for something else.

Each one of the SPST relays (the black squares) lay a resistor (the long white things) across one of the power supplies in the mainframe. There's a 12vdc, +33vdc , -33vdc, two 25vac, and a 17vac that is shared with the (supplies power to) the +12vdc supply. Each of the small orange squares is a DPDT relay, which i use to lay the meter leads across the relay-resistor pairs. These are selected with the front panel rotary SP12T switch (not wired up yet).

There's two transistors per slot in the mainframe, and by the specs Tektronix gives for them, they must be pretty poor transistors. Power dissipation of only 7 watts?? Anyhow, i make up a + and - 17vdc from one of the 25vac lines, and current limit power to the collectors and emitters of each transistor with a 50 ohm resistor. One switch position applies power to the resistors but leaves the transistor bases off, in this way if any one LED lights then there is a collector or emitter shorted to ground (probably by swarf in the mounting holes), and if both LEDs are on for a transistor, it's shorted collector to emitter. The next test is to ground the base, causing the emitter to pull up to near gnd, and the collector to pull down nearly to gnd, if any idiot LED doesn't light, the transistor is open.

Here's the details, the rats-nest wiring. It's perfboard, it's not etched copperclad. I want to see the design work before i make a permanent etched board.

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