Tag: Repairs

If it used to work, it can work again

MGE Ellipse 1200 Battery Arrangement

The SLA batteries in the MGE Ellipse 1200 UPS finally gave out. This picture shows how they’re arranged inside the box:

MGE Ellipse 1200 UPS – battery arrangement

They’re 12 V 5 Ah batteries that are about 12 mm thinner than the garden variety 7 Ah batteries you can get everywhere; they’re not the same size as the generic 5 Ah batteries you might think would work. Of course, there’s not enough room inside the stylin’ case for the larger ones, either. I’m thinking of using fatter batteries anyway and putting a belly band around the gap. Maybe an external battery box with a chunky cable burrowing through a hole in the UPS case?

For what it’s worth, APC absorbed MGE a while ago (so the MGE website redirects to APC), got Borged by Schneider, then spat out MGE’s consumer grade UPS units to Eaton. You won’t find any of that documented anywhere, but here’s the response from APC after I didn’t find this UPS on their list:

I do apologize; when APC was acquired by Schneider Electric, the single phase UPS line that MGE once offered was sold to Eaton. Eaton now provides support for the MGE single-phase products. We do not sell batteries for these models. You will actually need to contact Eaton for further assistance regarding the MGE Ellipse units. You may click on the link below to go to Eaton’s website:

http://powerquality.eaton.com/Default.asp

The Eaton website does have a battery replacement for this one, but sporting the dreaded “Contact us for price” notation. Given that I got the UPS cheap-after-rebate, I’m thinking maybe this isn’t worth the effort.

2011-07-22

Thing-O-Matic: Broken G0 Semantics in RepG 25

I upgraded to ReplicatorG 25 and the Thing-O-Matic promptly got weird: the initialization code slowed to a crawl. The motors ran fine, the motion was properly coordinated, but the thing moved at a minute fraction of its normal 100 mm/s.

This was most obvious on the first move to the center of the stage after homing the axes. If you peer into the source code, that instruction looks like this:

G0 X0 Y0 Z10	    (pause at center to build confidence)

The comment tells you exactly why I put that move in there when I first started tinkering with start.gcode: I long ago discovered that automation doesn’t always do what you want, so having a simple verification at the first opportunity sometimes pays off big.

Anyhow.

A bit of rummaging showed that RepG 25 has changed the semantics of G0, which is supposed to be a fast move to the programmed coordinates. Now G0 moves at the feed rate set by the most recent G1 and also accepts an F parameter, which it shouldn’t. I suspect somebody refactored the code and didn’t notice that G0 isn’t supposed to work exactly like G1.

There’s a RepG ticket for that.

The current start.gcode, just for future reference…

(---- start.gcode begins ----)
(MakerBot Thing-O-Matic with aluminum HBP and Z-min platform switch)
(Tweaked for TOM 286 - Ruttmeister MK5 stepper extruder mod)
(Ed Nisley - KE4ZNU - May 2011)
(- set initial conditions -)
G21		(set units to mm)
G90		(set positioning to absolute)
(- begin heating -)
M104 S210 T0	(extruder head)
M109 S110 T0	(HBP)
(- coarse home axes -)
G162 Z F1000	(home Z to get nozzle out of danger zone)
G161 Y F4000	(retract Y to get X out of front opening)
G161 X F4000	(now safe to home X)
G92 X-53.0 Y-59.0 Z117.0	(set XYZ coordinate zeros)
(- fine home axes)
G0 X-51 Y-57 Z115 F400	(back off switches)
G161 Y F200
G161 X F200
G162 Z F200
G92 X-53.0 Y-59.0 Z117.0	(re-set XYZ coordinate zeros)
(- manual nozzle wipe)
G0 X0 Y0 Z10	    (pause at center to build confidence)
G4 P500
G0 X40 Y-57.0 Z10	(move to front, avoid wiper blade)
G0 X56            (to wipe station)
G0 Z6.0           (down to wipe level)
M6 T0			        (wait for temperature settling)
G1 Y-45	F1000		  (slowly wipe nozzle)
(-----------------------------------------------)
(- Make sure the XY position matches the G92    )
(- home Z downward to platform switch)
G0 X56.4 Y7.6 Z3	    (get over build platform switch)
G161 Z0 F50	          (home downward very slowly)
G92 X56.4 Y7.6 Z1.50   (set Z height)
G0 Z6.0			          (back off switch to wipe level)
(-----------------------------------------------)
(- start extruder and re-wipe)
G0 X56 Y-45     (set up for wipe from rear)
G1 Y-57.0 F1000 (wipe to front)
M108 R2.0	      (set stepper extruder speed)
M101		        (Extruder on, forward)
G4 P4000  	    (take up slack, get pressure)
M103		        (Extruder off)
G4 P4000  	    (Wait for filament to stop oozing)
G1 Y-45	F1000		(slowly wipe nozzle again)
G0 X0           (get away from wiper blade)
(- manual splodge)
(G0 X0 Y-58)		  (to front center)
(G0 Z0.5) 		    (just over surface)
(M108 R2.0)	    (set stepper extruder speed)
(M101)           (start extruder)
(G4 P1500)       (build up a turd)
(- inhale filament blob)
(M108 R25)	      (set reversal extruder speed)
(M102)           (Extruder on, reverse)
(G4 P50)
(M103)		        (Extruder off)
(- build some pressure)
M108 R2.0	    (set stepper extruder speed)
M101           (start extruder)
G4 P50       (run for a bit)
(---- start.gcode ends ----)

I suppose I must add a feedrate parameter to each G0 as a workaround. Drat.

2011-07-11

Beard Trimmer: NiCd Rejuvenation

Strictly speaking, I do not have a beard: I simply do not shave (*). There being no money in selling Trimmers for the Non-shaving, a while back I bought a battery operated Beard Trimmer. The NiCd cells lasted for the predictable few years and recently gave up the ghost entirely: an overnight charged produced a weak buzz with no cutting action to speak of.

The case uses one-time snap-together latches, which makes dismantling it a challenge. Start by removing all the gimcrackery on the business end, then pry out the two latches holding the it-was-white-once cutting length adjustment ring. With that out of the way, undo the two latches inside the top and work your way down, prying the case halves apart in the way the overlap flange doesn’t like, so as to force the latches loose.

This picture shows the six latches, three on each side. The ones just to the right of the blue impeller require the most cursing:

Beard trimmer case and innards

The circuit board snaps out, with the two PCB contact areas clamped down by springy contacts leading to the motor.

Beard trimmer – battery charger PCB

The two NiCd cells boast of their High Energy, but they’re only 600 mAh. That’s actually too much for this high-drain, short-run application, as they don’t completely discharge. They’re held in place on the right end with a blob of hot melt glue:

Beard trimmer – NiCd cells

I unsoldered the cells and gave ’em a brute-force overnight charge at C/10 = 60 mA, then ran a discharge test (clicky for more dots):

Beard Trimmer – NiCd Discharge Test

Lookee that! The cells still deliver their rated capacity, even though they no longer worked with the stock charger. I repeated the slow-charge and discharge trick, which produced a perfectly overlapping trace.

Flushed with success, I unleashed the built-in charger overnight, then produced a third overlapping trace.

So they suffered from voltage depression, most likely due to never being completely discharged and then being overcharged far too often. That’s cured by a complete discharge and recharge, which worked perfectly.

I hack back the overgrowth when it gets bushy and recharge the trimmer when it seems to be getting weak, which used to take a week or two. That’s a bad way to maintain a NiCd battery, particularly as the PCB applies a very low load to keep its computronium running, but I have better things to do than babysit a beard trimmer. Honest.

Anyhow, assembly is in the reverse order and it’s perfectly happy again.

I probably won’t change my evil ways, so the next time I’m sure the battery will be really and truly dead.

(*) Not shaving adds about ten minutes a day to my life, which I regard as a fair tradeoff over the course of several decades. It also added a decade to my apparent age, Back In The Day when that mattered. Now it seems to knock off a decade, which isn’t entirely a Bad Thing.

2011-07-09
Casio EX-Z850 Camera Button Failure

The Casio EX-Z850 camera living in my pocket finally developed a problem. Two buttons on the back select the Review and Camera modes; the former stopped working, which means I can’t see pictures after I take them. The Camera button may still work, but because I can’t display pix, that’s pretty much moot.

Taking the camera apart require a Philips 00 screwdriver bit and some care, but eventually you’re confronted with this:

Casio EX-Z850 camera – opened

The buttons and the mode selector dial all connect to the same flexible PCB substrate, which ends up in this connector. You should ease the black pressure bar (seen edge-on here) upward to release the flex PCB:

Casio EX-Z850 button connector

As it turns out, the two buttons have a common contact that’s the second trace from the top in the flat cable. Both buttons have good snap action, good conductivity, and seem to work fine. That puts the problem deeper inside the camera, where I don’t see much point in going; I can certainly make things much worse and likely not make them any better.

In fact, it turns out that the two buttons on the USB/charging cradle don’t work now, either, which implies that the camera buttons run in parallel with those. So there’s something blown in the camera’s guts, which is definitely Bad News.

Back in the Bad Old Days, you used to take a picture and wait a week or two to get the results back from the drug store. Perhaps it’s fashionably retro to have a digital camera without a Review mode?

2011-07-03
Monthly Aphorism: On Non-Economic Repairs
- The skills we acquire fixing stuff that we don’t care about serve us well when we have to fix something that actually matters
Courtesy of John Rehwinkel.

A long time ago, I read this in E. E. “Doc” Smith’s The Skylark of Space:

He could study safeblowing fifteen minutes and be top man in the field

Even back then, I knew knowledge didn’t work that way. If your fingers haven’t done it, you don’t know how to do it. The more you do it, the better you get.

Go fix something!
2011-06-30
Gas Grill Igniter: Design Failure Therein

The Judges at the Trinity College Home Firefighting Robot contest use butane grill igniters to light the candles in the arenas, but the gadgets seem to have terrible reliability problems: very often, they simply don’t work. I brought a few deaders back to the Basement Laboratory this April and finally got around to tearing them apart.

It seems they don’t ignite because the trigger’s safety interlock mechanism shears the plastic gas hose against the fuel tank’s brass outlet tube:

Grill igniter with sheared gas tube

I tried putting a small brass tube around the (shortened and re-seated) hose, but it turns out the trigger interlock slides into that space and depends on the hose bending out of the way:

Grill igniter with brass tubing

So there’s no easy way to fix these things.

It seems to me that a device using flammable gas should not abrade its gas hose, but what do I know?

2011-06-18
Roof Work: Vent Stack Gaskets and Shingle Fungus

Part of the spring ritual involves cleaning the maple seeds out of the gutters, which also gives me an opportunity to inspect things up there. This year brought a revolting discovery:

Rotted vent stack gasket

It seems the rubber (?) seals around all three vent stack pipes have disintegrated. Now, the contractor installed these as part of the re-roofing project late in the last millennium, so it’s not like they came with the house. They’re an exact match for what’s currently available at Home Depot and I have no reason to believe new ones will last any longer. Sheesh.

The correct fix involves removing the shingles around the existing aluminum plates, installing new plates, and then replacing the shingles. That seems unwarranted, seeing as how the aluminum remains nicely bonded to everything, so I slipped some solid polyethylene shields around the vent stacks, tucked them under the uphill shingles, and hope that’ll suffice.

The discoloration on the roof is getting worse, except downhill from the chimney’s copper flashing. You can see one of the ugly new black plastic vent seals over on the right:

Copper effect on roof discoloration

I suspect the copper ions kill off the fungus, so, invoking Science, I tucked a foot of copper wire under the ridge vent uphill from a patch of fungus:

Anti-fungal copper wire test

We’ll see if that makes any difference. I suppose the next time I’m up there I should tuck a strip of copper flashing under the shingle on the other side of the chimney to see if a bit more surface area will have more effect.

2011-06-16