Why is the printer spouting nonsense... and who on earth tried to wire this plug?

A tale of entry-level electrical skills

On Call There's just one more day to get through before the weekend is upon us so burn a few minutes by chortling at the misfortune of others with On Call.

Today's tale from the telephones comes from "Steven" and concerns a mysteriously malfunctioning printer.

"I was called to look at an old Mannesmann Tally printer that was printing rubbish,"

For the younglings, Mannesmann Tally was a big a deal in the world of dot-matrix printers back in the last century. The company had even ventured into the world of inkjet printing before succumbing to the realities of the market as the century turned.

Back in the day the devices were not an uncommon sight, and Steven trotted over to inspect the machine. A print request was submitted and "sure enough, rubbish characters mixed in with the printout."

The printer was still under warranty, on a "return to vendor" basis, "so I duly packaged the printer up and sent it off."

"After about a fortnight, the printer came back: No fault found."

Steven returned the printer to the user, plugged it in and, being a conscientious soul, tried it out. The printer once more spewed garbage.

He tried a new printer cable. Still garbage.

He tried a different PC. Yup – garbage again.

After attempting more configurations, Steven returned the printer to the vendor once again. The machine boomeranged back to the office with another terse "No fault found" note.

The one thing Steven had yet to try was a different power cable. Regular readers will be unsurprised to note that this solved the problem – the printer worked perfectly.

At this point it is worth noting that all the power sockets in Steven's building had been replaced by ones with a T-shaped earth pin "in order to prevent people bringing in appliances from home". As such, all office devices had required a new plug. And, of course, the vendor (lacking its own T-shaped socket) had used a different cable.

"I removed the plug and had a look," Steven said.

"It turned out that some 'bright spark' had replaced the plug for this printer, and in doing so had wired the earth lead to the neutral pin and the neutral lead to the earth pin."

The corruption was the result of noise on the mains supply. Please use the comments section below to expand on the implications of wiring neutral to earth in this way.

Mystery solved! Steven reported the good news to the user, expecting to be showered with gratitude. Instead, "he went into a fit of swearing and cursing!"

What was the problem?

The user replied: "The same electrician who changed that plug rewired my house last week!"

Oops.

It's always DNS unless, of course, it's some ham-fisted wiring. Have you ever spent hours working a problem, only to find the simple solution ripped open a whole bag of angry monkeys? We certainly have, and On Call is happy to share your pain. ®