Sep 122017
 

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.

 Posted by at 11:40 pm
Sep 272012
 

Once again, I was doing something dangerous: despite being a programmer, I chose to carry not just a screwdriver but also some power tools.

Two weeks ago, I had a plumbing crew remove our old bathtub. It was way overdue:

It took them no more than a couple of hours to reduce the bathtub to this:

And by mid-afternoon, they were done. The new bathtub was installed. Actually, let me emphasize: ONLY the new bathtub was installed:

From this point on, I was on my own. It was by choice: I dislike having workmen in my house and in any case, these are skills that, I think, are well worth learning.

Having never done tiles (or for that matter, sheet rock) before, I was taking things slowly. (Hey, I am also just a few months shy of fifty, somewhat overweight, and I usually spend my days in an armchair sitting in front of a computer.) Even so, a few days later, I was done with all the preliminary work: notably, the installation of tile backer drywall:

The plastic sheets were put in there so that we could use the bathroom even while it was still under construction.

Next came the tiles. The tricky bit (for me anyway) was to cut tiles around the faucet and other fixtures. I was able to cut pretty decent holes using a tile cutter bit in my “Roto-ZIP” tool:

And thus it came to be that a little less than two weeks after the plumbers left, the tiling was done:

There was, of course, still more work to do. First, I had to wait a few days for the adhesive to set before grouting the tiles. Once I completed the grouting successfully, I had to wait another few days before I could spray the new grout with sealant. It was only at this point, namely today, that I sealed the edges of the tile using silicone. Finally, once the fixtures were reattached, the job was at last done:

Needless to say, I am mighty proud of myself. In fact, I’ll probably be insufferably proud for the next few days (that is, unless the tiles start popping off, in which case my insufferable pride will rapidly turn into an overwhelming sense of embarrassment.) There is still a little bit of cleaning up to do, and eventually, repaired bits of wall around the tiles will need to be repainted. I may apply a bit of paint for protection, but the real paintjob will have to wait; I am considering replacing the vanity (the sink definitely needs to be replaced) and I am also considering replacing the floor tiles, which are old and have developed a few minor cracks over the years.

But not this year. For now, I prefer to return to my regularly scheduled programming job and put down my screwdriver.

Phew!

 Posted by at 5:32 pm
Oct 302010
 

I am 47 years old, but up until last week, I never ever painted a room. I knew more about how paints behave on spacecraft surfaces than on drywall.

Well, this is no longer true. I just finished the walls, window, door, and floor in our small bedroom:

Yes, I am proud of my handiwork. Our cats appear to be satisfied, too:

But no, I am not planning to give up my day job.

 Posted by at 5:51 pm
Sep 262009
 

I was a very brave person today… I peed in a toilet that I just finished installing.

So far, no sign of leaks below.

 Posted by at 1:05 am
Sep 252009
 

I’m most pleased with myself tonight. Maybe I have an aptitude for the experimental side of physics, too, as it appears that I was able to repair successfully my subfloor around the leaky toilet. I took some pictures:

Next task is to finish the floor and put the new toilet in. Maybe tomorrow, maybe not… I’m rather tired, so I might skip a day. But then again, I seem to be on a roll…

 Posted by at 2:18 am
Sep 242009
 

There are certain areas of life where decades of computer expertise are quite useless, and even a reasonably thorough knowledge of theoretical physics is only of marginal use. Replacing the rotted subfloor around a leaky toilet is one such area.

Yet this is what I am presently engaged in. So far so good… using some rather evil, foul-sounding power tools, I managed to cut out much of a square hole around the drainpipe, I’m only having trouble with some corners where the power tools don’t reach. Unfortunately, I found out that the subfloor in this bathroom is actually an inch thick, as opposed to the standard, 5/8″ board that I already bought… oh well, it wasn’t a big expense anyway, and perhaps I can use that board for some other purpose later on.

For now, it’s back to Home Depot to get a piece of inch-thick wood and also some advice on cutting out those nasty corners. Maybe they can suggest a method that would be slightly more efficient than the hammer-and-chisel approach which I attempted, with¬† some limited success.

While I’m at it, I shall also inquire as to whether it is possible for them to cut my boards to shape to fit around the drainpipe, so that I wouldn’t have to attempt such precision cutting using my fairly limited skills and perhaps less-than-adequate set of tools. Not to mention that I value my fingers, and prefer to have all ten of them in the right place and in full working order after I’m done with all this…

But for now, it’s rest time. I have this nasty tensor algebra program to tackle, but no matter how difficult it is, I sweat a lot less doing it than when I’m cutting a subfloor with a circular saw.

 Posted by at 3:30 pm