On Call Life is filled with random events, but The Register tries to make readers’ lives just a little more predictable by always using Friday morning to bring you a new instalment of On Call – the reader-contributed column that shares your tech support stories.
This week, meet a reader we’ll Regomize as “Benny” who in the 1990s worked for a large Australian telco and was sent to fix a recurring problem at a gardening shop – the sort of big box store that sells plants by the acre, and tools by the wheelbarrow-load.
This shop’s point of sale card reading terminals were failing several times a day and Benny was sent to investigate.
"They had a master terminal that had a line back to a Honeywell DPS6 at one of the local exchanges, and the other terminals were connected to the master terminal on an RS485 bus," he explained.
"We had switched to the backup modem at the exchange, run extended Bit Error rate tests on the line, replaced the master terminal, tested the RS485 cabling, and couldn't find anything wrong."
Benny therefore set up a protocol analyser on the RS485 bus and even rustled up a couple of differential probes he hooked up to an oscilloscope "to have a look at the data and clock lines."
With that rig in place, Benny settled in to watch the systems in the hope of spotting a bug.
"I sat there most of a day waiting for it to crash and of course it didn’t skip a beat," Benny told On Call.
He decided this was a classic case of "Technician Aura," the weird cosmic force that means bugs disappear when a tech support person arrives to fix them. Eventually he gave up trying to find the problem and started writing up a report about the mess.
As Benny picked up his pen, a colleague arrived to ask how the job was going and put his GSM phone next to the master terminal.
As the two bantered, the phone rang – and staff at the shop immediately complained of a crash.
"It turned out that the cashier usually placed her phone on the shelf next to the payment terminal," Benny explained. "When I hooked up my monitoring gear, she was forced to relocate to another cash register. When she worked at her usual station, whenever her phone rang, it caused enough interference to crash the payment system."
Have you suffered from "Technician Aura"? If so, try to suppress it long enough to click here and send On Call an email. The mailbag could use a little plumping at the moment, so don’t be shy! ®
Source: The register