I have an old (11 years, to be precise) Konica-Minolta magicolor 2450 laser printer, with the duplexer option.
The quality of this printer’s output is superb, but mechanically, it was never perfect. Just a few weeks after I purchased it, it stopped printing. Faced with the prospect of having to return a 20+ kilo monster, I figured I’d take my chances and look for the cause; after partially disassembling the printer and re-seating some internal mechanical parts, it started printing again.
It worked for many years, but it was becoming rather unreliable. Sometimes, the output was shifted down from the top margin. Paper jams became frequent. It started to fail in mysterious ways, such as complaining that a toner cartridge was missing. Eventually, it stopped printing altogether; every attempt resulted in a paper jam, as the last set of rollers, responsible for pulling the paper out of the printer, no longer worked.
I bought another printer in the meantime, so I retired the mc2450. But I loathed the idea of turning it into e-waste or sending it to a landfill. Today, I decided to take one final look at this fine machine, to figure out what could possible be wrong with its mechanism.
Eventually, I stumbled upon a set of YouTube videos, which offered advice about cleaning some solenoids. Say again?
Solenoids are used in some internal actuators that turn on and off specific parts of the printer’s mechanism. These events are timed with precision. And as it turns out, little plastic pads that are used, I presume, to eliminate clicking sounds and perhaps reduce mechanical wear in the metal parts that are actuated by the solenoids became sticky over time. Just a teeny bit sticky. But that teeny bit is enough for the actuator to become a little lazy. Move a little too slowly. Not much… a few ten milliseconds. But when the paper moves through the printer at, say, 20 cm/s, 50 milliseconds amounts to a centimeter… more than enough for timings to be off and for the mechanism to fail.
Still, it sounded like a stretch. After all, the stickiness was just barely noticeable. Nonetheless… I followed the video’s advice (except that instead of removing/replacing the plastic pad in question, I covered them with kaptonthread seal* tape.) After I reassembled and fired up the printer (and fixed a paper weight adjustment that I managed to set incorrectly), presto: it was printing test pages flawlessly!
Yippie. My old printer was working again. I put it fully back together, and decided to give it another test, this time with its duplexer installed. A huge disappointment: as the paper was feeding through the duplexer, it acquired a nasty fold, very consistently, each and every page. What could possibly cause this?
By this time, I downloaded the service manual for this printer, and studied the diagram of the duplexer a little. It looks deceptively simple, just like an extra back cover for the printer, but it hides complex machinery inside. And guess what… a solenoid actuator, too. And when I disassembled the duplexer and looked at the bit in question, sure enough, its plastic pad was sticky. Ever so slightly sticky, but the stickiness was (just barely) noticeable.
Another few square millimeters of thread seal tape later, after reassembly, my old printer is now printing double-sided documents again flawlessly.
This exercise was not just satisfying but also very educational. That such a tiny flaw can cause all these symptoms. And symptoms that I attributed to (possibly) bad sensors, misaligned or failing mechanical bits, or aging plastic were all caused by actuators that were slowed down, by no more than a few ten milliseconds, tops, by a bit of sticky plastic. Amazing.
*Someone told me it was kapton tape. No, it’s really teflon. My mistake.