Posts Tagged Repairs

HP 7475A Plotter: Inmac Ball-point Pen

Just for a change, I punched a new-old-stock Inmac pen from its sealed blister pack, only to find that it left a spotty trail. These being easy to refill, I popped the top, flipped the fiber reservoir, added ten drops of HP2000C black (i.e., not the crappiest ink I’ve ever used), and scribbled a few feet to get it started again. It left a good-enough trace, so I ran an A-size plot with the ball pen, two liquid ink pens, and a refilled ceramic pen:

HP 7475A - Inmac ball - liquid - ceramic - pens

HP 7475A – Inmac ball – liquid – ceramic – pens

It’s a bit pallid compared with the black ceramic pen. The line is continuous and, in comparison with all the other plotter pens in the collection, very very very fine.

Turns out that it’s a miniature ball-point pen:

Inmac ball pen tip

Inmac ball pen tip

I’m certain that water-based inkjet juice isn’t the right stuff for a ball-point pen, which may account for the lack of color. It’d be most appropriate for a document with fine text details, not that I must plot any of those at the moment.

There’s a bag with a dozen more of ’em in various cheerful colors, so, if I could just think of something that needed stubby ballpoint pens, I’d be all set.

It might be intended for a different HP plotter that applies more downforce to give the ball more encouragement. We’ll never know…

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3D Printer Platform Alignment: Details Matter

Being that type of guy, I measure the single-layer skirt threads to keep track of the platform alignment. Most of the time, nothing happens, because the M2 has a remarkably stable platform, but some of the objects I’d done in early August showed more than the usual variation and, worryingly, no discernible trend.

Successive sets of thinwall hollow boxes showed the instability:

M2 Alignment measurements - 2015-08-09 - 1

M2 Alignment measurements – 2015-08-09 – 1

Adjusting the platform alignment between each of those sets produced no consistent effect, which is most unusual. The X in the bottom set shows where that thinwall box came unstuck from the platform, indicating that the clearance was considerably more than the nominal 0.25 mm layer height.

Peering under platform revealed something else that was quite unusual:

M3 washer - bad seating

M3 washer – bad seating

That washer should be flat against the spider mounting plate. My first thought was a burr on the plate, but that didn’t make any sense, as the plate was clean & smooth when I installed the platform; I’d enlarged those holes with a fine file and would have checked for burrs as part of that operation.

Removing the screw nut and extracting the washer revealed the true problem:

M3 washer with burrs

M3 washer with burrs

It’s a bad washer!

Tossing that one in the trash and installing a good washer put everything in order:

M3 washer - proper seating

M3 washer – proper seating

Well, that’s after re-doing the alignment to un-do the previous flailing around, of course.

As nearly as I can tell, that washer sat there without causing any trouble since I installed the hotrod platform. or, more likely, when I repaired a failed screw. In late July I poked the platform to measure how much it moved under pressure, which apparently dislodged the washer and put the burr in play.

That’s how sensitive a 3D printer is to mechanical problems…



HP 7475A Plotter: Zombie Pens

Following madbodger’s recommendation, but finding no local sources, a bottle of Koh-I-Noor Rapido-EZE Pen Cleaner solvent arrived. It’s billed as a solvent & cleaner for drafting ink, not plotter ink, which seems like an unnatural restriction.

I’d previously tried refilling some fossilized pens, only to find that the ink simply won’t flow through a nib filled with dried ink. So the pens you’ll see here have refilled reservoirs atop nibs that don’t write.

Dismantling the Koh-I-Noor black pen produced this unsightly mess:

HP 7475A - Koh-i-Noor black pen parts

HP 7475A – Koh-i-Noor black pen parts

I pushed the nib out of the shell using a pin punch, pretty thoroughly crushing the tip in the process. The ink reservoir looks like some sort of fluff inside a plastic sleeve, with a hole left by the butt end of the nib and a crust left by the evaporating ink. I scraped off the crust, put the nib in a cylinder filled with solvent, and let it sit for a few days, after which most of the black ink had vanished.

I reassembled the pen with the blunted end of the nib inside the body and the reservoir flipped end-for-end, in the hope that would work better.

Trying a different tactic with a Staedtler green pen, I removed the reservoir, filled the body with solvent, and dunked the tip in a solvent bath:

HP 7475A - Staedtler pen - nib soaking

HP 7475A – Staedtler pen – nib soaking

After a few days, the body was still mostly full of solvent, so it’s not flowing freely through the nib. Perhaps leaving the nib in air would encourage the fluid to move outward, at the risk of drying the nib even more.

Refilling them with inkjet printer ink produced this:

HP 7475A - Koh-I-Noor 2 - Staedtler 3 - zombie pens

HP 7475A – Koh-I-Noor 2 – Staedtler 3 – zombie pens

Pen 2, the gray K-I-N trace, seems a bit pallid, likely due to using cheap black inkjet ink. Apart from that, it’s continuous and presentable.

Pen 3, the green Staedtler, remains in the land of the undead; its ink flows better than before, but not enough to be worthwhile. The demo routine writes the annotation first and those characters came out well enouigh.

The other two pens also carry refilled ink: Pen 1 = ceramic tip, Pen 4 = Staedtler fiber (which, judging from the cap color, started out as gray and has become much darker after the inkjet ink refill).

All in all, a modest success and I’ll try again later. Better, however, to refill each pen before it dries out, as with the two “good” pens.


Casio EX-Z850 Shutter Failure

After nine years, the shutter on my muchrepaired Casio EX-Z850 camera has failed, producing images with horizontal white lines:

Casio EX-Z850 Shutter Failure

Casio EX-Z850 Shutter Failure

That can also come from a sensor failure, but it takes perfectly good movies. That’s the differential diagnosis for shutter failure, because movies don’t use the shutter.

The shutter still functions, in that peering into the lens shows the shutter closing as it takes a picture, so I suspect it’s gotten a bit sticky and slow over the years. None of the various shutter-priority speeds have any effect, which means that the shutter isn’t responding properly.

A quick read of the service manual shows the Field Replaceable Unit for this situation is the entire lens assembly. Back in the day, a new lens assembly came with its own calibration constants on a floppy disk that you’d install with Casio’s service program (the latest version ran with Windows 98!) using a special USB communication mode triggered by a Vulcan Nerve Pinch on the camera. At this late date, none of that stuff remains available.

While I could take the camera apart and crack the lens capsule open, I doubt that would make it better and, in this case, ending up with a crappy camera doesn’t count for much. Extracting the lens assembly requires dismantling the entire thing, which, frankly, doesn’t seem worth the effort…

That image is number 7915: so it’s taken a bit over two images per day for the last nine years. I can’t swear the counter has never been reset, but that seems about right.

Sic transit gloria mundi, etc.


Kenmore 362.75581890 Stove: Weak Oven Igniter

The burner in our oven failed in December 2006, probably because the charred remains of an insect produced a hotspot:

Burned Oven Tube Overview

Burned Oven Tube Overview

That replacement burner came with its own igniter that failed after 8.5 years, with symptoms of slow oven ignition and the occasional smell of propane.

In normal operation, the igniter element glows yellow-hot for a minute or so before the valve opens, gas flows over the igniter, there’s a muffled whoomf, and the oven begins heating. The igniter remains powered as long as the oven is on, emitting a baleful yellow glare through the slots in the oven’s lower cover.

It consists of a ceramic base holding a stout resistance heater that apparently suffers from increasing resistance as it ages, reducing the current to the point where it won’t activate the gas valve.

I didn’t know that, either, but Google sees all, knows all, and tells most.

The gas valve label says it requires 3.3 to 3.6 A from the heater to turn on the gas:

Kenmore range oven gas valve - data plate

Kenmore range oven gas valve – data plate

But the old heater was good for barely 2.6 A (there’s a bit of parallax in this view):

Kenmore range oven gas valve - weak igniter current

Kenmore range oven gas valve – weak igniter current

Igniters range from $18 to upwards of $60 on Amazon, so I picked the cheapest one, waited two days, installed it, and measured 3.5 A at First Light, down to a bit over 3.0 A at running temperature. That’s on the low side of the valve’s spec, but it seems happier with an extra half amp.

We’ll see how long this igniter lasts; maybe next time I’ll double my spend…


HP 7475A Plotter: Ceramic Tip Pen Autopsy

It turns out that the ceramic-tip plotter pens don’t come apart at the top of the flange as I expected. Instead, there’s a snug-fitting plug with a tapered top and an invisible joint at the end of the body tube:

HP7475A Plotter - ceramic pen - disassembled

HP7475A Plotter – ceramic pen – disassembled

Refilling a pair of defunct black ceramic pens didn’t bring them back to life: an ample supply of fresh black ink never made it from the fluff to the nib. Soaking the nibs + fiber shafts in 10% ethanol for a day created an unappetizing black vodka shot that did nothing to get the ink where it needed to be.

The right time to refill those pens would have been, oh, probably a decade or two ago…

Some stuff, you just gotta throw out!


HP 7475A Plotter: Refilled Pen Performance

Squirting brightly colored CMY ink mixes into an assortment of not-quite-dead-yet plotter pens produced reasonable results:

CMYK Refilled Pens - plot overview

CMYK Refilled Pens – plot overview

The blotches on the legend in the lower left corner show that a refilled plotter pen can accumulate a droplet of ink around its nib, which should come as no surprise. I wiped off the excess immediately after refilling each pen, let the assortment sit for a few hours to (presumably) let the new ink reach the nib, and wiped them off before inserting them in the plotter’s pen carousel. All I can say is that I used up a bunch of paper towels in the process…

A closer look at the plot shows Pretty Good If You Ask Me results:

CMYK Refilled Pens - plot detail

CMYK Refilled Pens – plot detail

The two blue-ish pens have less flow than the others, resulting in dotted lines that should be continuous. As nearly as I can tell, that’s a function of how much OEM ink has solidified in the fiber nib and, most likely, the fiber rod that draws ink from the sponge reservoir inside the body.

And, of course, the colors produced by adding CMY printer ink to the surviving OEM ink aren’t found in any catalog. I’m also blithely ignoring the difference between the inks inside plotter pens intended for paper and those for overhead transparencies; at this late date, that’s defined to Not Matter.


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