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Tektronix 7854 Waveform Keyboard Rebuild

Posted on August 15th, by Shaun Merrigan in Electronics, Oscilloscopes, Tech. Comments Off on Tektronix 7854 Waveform Keyboard Rebuild

Tektronix 7854 Waveform Keyboard Rebuild

From the Tek Wiki:

The Tektronix 7854 Waveform Processing Oscilloscope, introduced in 1980, is a 400 MHz combined analog / digital mainframe in the 7000 series that takes two vertical and two horizontal 7000-series plug-ins. In addition to a conventional analog (real time) scope, it contains an equivalent-time sampling 10-bit digitizer and a programmable waveform processor with GPIB interface. The waveform processor can be programmed using a detachable calculator-style keyboard, using postfix operators (“reverse Polish notation” like HP calculators) that operate on entire waveforms, not just individual numbers.

Tek 7854 Mainframe #2 after cleaning

Tek 7854 Mainframe after cleaning


It is to the repair of the detachable keyboard that this post is devoted.  I purchased a keyboard for a reasonable price only to find that some keys were intermittent, and some did not work at all.

Opening up the keyboard showed that it was filled with debris:

Tektronix 7854 Case Dirt and debris

The membrane keypad likewise was contaminated:

Tektronix 7854 Keyboard Sand and dirt contamination

This keyboard must have been stored for 20 years in a desert warehouse somewhere in Arizona or New Mexico to accumulate all that sand.  The solution was to clean the keyboard thoroughly, which involved complete disassembly, repeated rinses with clean water, dirt removal with a soft toothbrush, and several rinses in methanol to carry away all the cleaning water.

Here is the cleaned and reassembled keypad (note the single unused pad):

I found that several of the polymer “return springs” were damaged or cracked.  Low surface energy epoxy repaired these otherwise unobtainable parts.

And the reassembled keyboard:

Tektronix 7854 Waveform Keyboard Rebuild

Testing the keyboard with my 7854 mainframe revealed that it functioned properly; all the keys worked and there were no issues.

Thanks for your interest.

Shaun Merrigan

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