Analog Angle Article

Scotty or Geordi, please contact me immediately

Like many of you, I watched lots of the Star Trek series in its various versions. While I was impressed by the transporter and warp drive, they required new physics beyond our present knowledge. In contrast, what really amazed me was the skill of the engineering crew. Most impressive was when they came upon an alien, completely unknown relic or spacecraft, and were soon able to get it running, connect to it, and even transfer data and power. To me, that connectivity was even more impressive than anything else.

I was reminded of this recently, as I too faced the challenges of debugging the unknown. I acquired a discarded high-end bicycle-style exercise machine, with the caution that it “sort of worked.” Though there was no user manual, I wasn't worried about learning to operate it; I would figure that out through trial and error. But the lack of a shop repair manual, that was a different story

Yet diagnosing and fixing something you have little information on, that's the engineering fun part, right? Some basic web searching told me that this unit used an alternator to drive a resistive load, which you could vary from the front panel. (I also learned there were a lot of other people looking for the user manual, as well!). My further tests implied that the internal 9V battery was used solely for the initial start up of the display, and once you got the pedaling going, the alternator provided the display's actual operating power. But I still didn't know what the architecture of the design looked like.

So it was on to the intriguing engineering task of trying to determine what was inside, and what was working or not, by a combination of inspection, poking, probing, and collecting evidence of what might be inside. The machine worked occasionally, which was both a help and a hindrance. The next step was putting together some speculative hypotheses of what was happening, as well as some tests to verify these.

Perhaps there was a loose or intermittent connection? Was there a centrifugal switch that closed at a certain rpm, but wasn't working properly? Did the alternator's ac/dc converter have limited output-hold time, due to a marginal capacitor? All good ideas, but how to test them? Could I figure out how to bypass certain sections, or override them, to at least localize the problem or support/deny a theory, despite the lack of technical documentation?

I'm still working on it, unlike Scotty or Geordi. And if anyone out there has a repair or user manual for the LifeFitness LifeCycle 5500HR Upright Exercise Bicycle, let me know!

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