Techie Solved Supposed Software Problem By Waving His Arms In The Air

On Call Welcome once again to On Call, The Register's reader-contributed column that each Friday serves up your stories of biting into half-baked tech support problems.

This week, meet a reader we'll Regomize as "Charlie" who once worked as field service engineer for a company he told us "installed computers for various large customers."

In this story, Charlie got the job of visiting a bread factory where two machines communicating over a serial cable were intermittently glitching. Charlie was told this was a software problem and sallied forth to fix it.

"I arrived about 10 am and started testing the software," he told On Call, but found nothing wrong. "All the software was installed properly and at the correct versions," he wrote.

Checking out the hardware seemed the obvious next step. Charlie tested the performance of all ports, probed cables to ensure they were in working order, and found all was shipshape.

Next: Checking DC output voltages. Again, all good.

Baffled, Charlie decided it was time for lunch. As you would when surrounded by the smells of bulk baking.

"While sitting there, listening to the many huge machines churning out various breads and pastries, I turned my multimeter to AC voltage and measured what my body was picking up from the air," he told On Call. Doing so involved "Opening and closing my arms to measure different distances using my body as an antenna."

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The client thought that was hilarious behavior and asked why Charlie was waving his arms about instead of enjoying my lunch.

The multimeter provided the answer as it picked up five volts AC when Charlie held the probes far apart.

"I re-measured the communication cable for AC," Charlie told On Call. His conclusion? "Even though the serial cable connecting the two computers was shielded, AC voltage was leaking in and changing the DC signal patterns just enough that sometimes a zero or a one was read wrong at the other end."

Which was why the computers were glitching.

Charlie's client found a nicely robust grounding strap. Charlie used it to tie the two computers together so they shared a common signal ground.

The glitches stopped.

"I had been sent to diagnose and solve a software problem," said Charlie as he concluded his tale. "The solution turned out to be hardware."

Charlie sent his contribution in response to our request for stories about tangential fixes for tech problems. If you have such a story – or have found yourself in a stranger place than a bakery to deliver tech support – click here to send us your slice-of-life story so we can use your sweet morsels of experience on a future Friday. ®