Techie solved supposed software problem by waving his arms in the air
- Reference: 1746170952
- News link: https://www.theregister.co.uk/2025/05/02/on_call/
- Source link:
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.
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"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.
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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.
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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."
[5]Techie diagnosed hardware fault by checking customer's coffee
[6]Need a Linux admin? Ask a hair stylist to introduce you to a worried mother
[7]Users hated a new app – maybe so much they filed a fake support call
[8]How do you explain what magnetic fields do to monitors to people wearing bowling shoes?
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."
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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 – [10]click here to send us your slice-of-life story so we can use your sweet morsels of experience on a future Friday. ®
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[5] https://www.theregister.com/2025/04/25/on_call/
[6] https://www.theregister.com/2025/04/18/on_call/
[7] https://www.theregister.com/2025/04/11/on_call/
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Didn't they need to use a cereal cable instead?
Charlie seems like a down to earth kind of chap...
... in fact he came to be known as Able Baker Charlie.
Bonus points if you remember all the old phonetic alphabet.
Glider pilot here: Remember the phonetic alphabet? I USE it every day I go flying.
You use the Able Baker Charlie one? The glider pilots I knew (300 Hrs P1 till EASA demotivated me) were generally pretty old, but not that old.
The next one is "dog", do I get a prize?
Doughy
He certainly rose to the occassion after the first proof.
I just knew that the commentards would manage to jam in a loaf of buns
Chair on the floor tile
We had a problem that when someone sat in front of a computer, the screen had problems. It was due to a floor tile squashing a cable. When you wheeled the chair over the floor tile - the screen went funny. When people came round to fix it - they didn't use the chair, but stood around the floor tile, and so it worked.
We had a problem once with an airport-based customer complaining that when they were printing from our software (using Okidata dot matrix printers) it was fine a lot of the time, but was intermittently inserting garbage into the printouts.
They swapped out the PC, the printer, the cables, but still no joy, until we sent someone to site to diagnose it.
Turns out the serial cable from the PC they were using was running next to a baggage injection belt at a check-in desk - and if someone activated the injection belt while a print job was on the wire, that was the cause of the data corruption. Bought a network card for the printer and chucked the serial cable in the bin.
I was called in ...
... to fix a similar problem after a similar fix had been applied.
Burned out one of the network cards the instant the "ground strap" was connected. And then a second network card, which is when they called me.
The motherboard catching alight tipped the geniuses off that there might be an issue, or their may have been three dead cards. Or six.
Be very, very careful when tying equipment grounds together, even within the same building. Things are not always as simple as they seem.
Re: I was called in ...
Well, if the two machines are powered from different phases of a three phase supply... yeah... not good.
Yep
I guess they were using RS232, but it would have been better to use a differential signal with transceivers that can tolerate ground differences.
Re: I was called in ...
That sounds suspiciously like a ground loop.
Seen quite a few over the years.
Where can I get proper dwarf bread?
GNU PTerry.
You don't get Dwarf bread, you make it.
First, you fire up your favorite forge. Let us know when it's good and hot for further instructions.
Forging dwarf bread like mother did is so difficult, far away from the mountains. You just can't get the right ingredients. They so often end up too soft, without sufficient gravel, and they hardly last a year.
They didn’t know they were born!
We ‘ad the bake our own gravel.
It's a wise dwarf ...
" Forging dwarf bread like mother did is so difficult, "
That know which of their † parents is their mother if recall the dwarves' peculiar take on gender identity.
† bugger I've used the gender non specific 3p.sg. pronoun but suits the dwarf world view.
Dwarf bread? Gneiss!
No Surprise
This is a well known issue with any process that generates large amounts of dust with rapidly moving materials. Printing presses are very similar. People are often surprised at the amount of paper dust that is created. Quite substantial cross-bonding and a good earth is pretty much obligatory.
Oh, and you also get the double whammy of elevated fire risk, and breathing problems for the workforce.
sometimes a zero or a one was read wrong at the other end
This, kiddies, is why you never shove important data down a wire without some form of active flow control - even if it's something as simple as breaking the information into 128 byte blocks (or whatever is convenient) and then sending a checksum.
Smarter protocols may combine that with some degree of built in error correction, but whatever, assuming that what goes in matches what comes out is a rookie error.
CAN
Yep, which is where things like CAN bus come in handy - it can handle ground differences and all transfers are validated and re-tried if there are any errors (so the receiving end only ever gets valid data*).
* Nearly - it is theoretically possible for the CRC check to pass a bad frame, but it's so unlikely that only a few system need to worry about it.
Were there any currents in the pastries?