Tektronix 2236 Repair

The Tektronix 2236 two channel 100MHz oscilloscope, circa 1985, has an interesting multi-function display and built-in multimeter. The display is a nine-digit vacuum fluorescent tube that is used to display AC and DC voltage, resistance, diode check, temperature, frequency and period values as well as the timebase B delay setting and more. It’s a cool thing to have built into a piece of gear like this and not have to give up any more bench space.

But this VFD is aging, and has grown very dim. With the room lights on it is impossible to read. I was inspired by Todd Harrison’s recent video, in which he troubleshoots and repairs the radio in his Jeep. It too has a VFD and had gone out completely. So it was time to do something about this problem and stop squinting and working in the dark. The process led me to a suspect CD4027 J-K flip flop as the culprit, and not having one on hand to replace it

I had the idea of programming a TI MSP430 microcontroller to emulate the behavior of this chip. I did so, and was able to trigger it from the clock pulse on the suspect chip. Then I lifted a few components out of the scope’s display circuit and injected my own flip flop output from the MSP430 back into the scope to drive the VFD.

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