Repairs « Keith's Electronics Blog

Archive for the ‘Repairs’ Category

Repairing a Soundcraft Spirit E6 Mixer Switching Power Supply

Sunday, April 19th, 2009

A few weeks ago, John mentioned to me that one of the audio mixers in the art and technology / Internet radio station lab had stopped powering on. I said I’d have a look at the power supply and see if I could fix it, and he sent it with me. Turns out we both got a little more than we bargained for — I in terms of effort required and he in terms of time without the mixer.

I didn’t know whether it’d be a linear or switching power supply, and it turned out to be switching. I figured it’d just have some baked electrolytic capacitors I could replace, and it turned out that was just the beginning.

I’ve got it mostly fixed now, and it’s been a long and interesting road.

(more…)

Posted in Circuits, Inside, Repairs | 154 Comments »

Fixing My Wife’s Curling Iron

Saturday, March 14th, 2009

When my wife leaves her curling iron on top of a note that says “Non-connected wire somewhere? goes in & out of power,” my first thought is, who taught you English?; and my second thought is, I better stop making fun of her long enough to get this fixed before she gets home from work.

My belated third thought is, I finally get to see how the infinitely-spinning power cord connection works . . . and I bet it’s the problem.

It’s tough always being right.

The power cord has a connector that looks a little like an RCA plug, except the barrel portion’s outer surface contacts the jack’s leaf instead of the inner surface contacting a barrel jack.

You can see the pitting on the leaf where the contacts had arced, probably at least in part due to oxidation of the surfaces. Also, the leaf was twisted so it was making contact only with the leading edge of the barrel instead of with the whole face, which exacerbated the problem by reducing the contact area to a very small point that became completely pitted.

After smoothing the pitted area and polishing the tip and ring leaves and the tip and barrel with 600-grit sandpaper, I reinstalled the power cord and carefully twisted the barrel leaf parallel to the barrel so they mate over a larger surface area.

Once the whole iron was reassembled, I plugged it in and watched its power lamp while spinning the cord around. No further problems that I can see. So it now, ah, has a connected wire somewhere and only goes in power.

Update 16-Mar-2009:

Turns out the power plug fit loosely in the bathroom light fixture receptacle and I just needed to bend the prongs out a bit. Oy vey.

Posted in Inside, Repairs | 5 Comments »

Fixing an LED Sign

Sunday, March 1st, 2009

My wife is working a couple of evenings a week for a tax preparer who used to work for her when she was an H&R Block office manager. Friday night he was taking down his $300 sign out of the window to throw it away because it had a few dark LEDs. She told him no promises, but I might be able to fix it because I do stuff like that every night.

And yeah, she was right.

I’m actually not sure I’ve seen all the failures the sign has to exhibit, but I’ve fixed two overt and two covert. The obvious ones were the dark LEDs in the white “M” and “E.”

The less obvious ones were that the pull-chain switch at the bottom doesn’t shut the sign off, and that the DC power plug pops out of the jack.

Opening It Up

The sign is made of two plastic sheets sandwiching a thicker plastic frame. The front must be glued on, but the back is screwed on for repairability. Actually, given what the inside looks like, I have my doubts that the manufacturer ever considered repair; I suspect screwing the back on was just the first thing that occurred to them.

I’m (mostly) not knocking the schematic — many parallel series chains of LEDs is the only reasonable way to design something like this. And making chains of three each blue and white LEDs but five red LEDs is also reasonable, given the respective voltage drops.

But I do take issue with stacking three LEDs with 3V drops on a 9V (nominal) unregulated power supply. The supply happens to run about 9.7V under the load of the sign, which leaves .7V across the 150Ω current-limiting resistors, hence just under 5mA LED current.

Leaving that low a voltage drop across the resistors makes the LED current (and brightness) incredibly susceptible to variation in the actual voltage of the unregulated power supply: a power supply change from 9.7V to 10.4V seems insignificant but would double the (white and blue) LED current. Worse, a drop from 9.7V to 9.35V would halve it.

Mainly, though, it strikes me odd that the sign is wired with leftover four-pair UTP (network cable). Was this thing built in some guy’s garage with stuff he pulled out of the dumpster at work? (Wait, did I build this thing??? )

Fixing the Power Connection

First things first — I started with the power connection so I wasn’t fighting it the whole time I was testing and repairing the rest of the sign.

The jack is recessed into the frame. The manufacturer made some effort to get it close to the outside and minimize the amount of recess; but the correct recess for this jack is zero. The plug is designed to make good mechanical contact when it’s sunk completely into the jack; before that point, the springiness of the jack’s outer contact pushes the plug back out of the jack, which is exactly what was happening.

The solution, or I should say hack, was to remove a corresponding amount of rubber from the plug’s molded barrel insulation, so it could once again fit the depth of the jack properly. No further problems.

Dead LEDs

Next I tackled the dead LEDs. A series string of three was dark in the M, leading me to supect one LED burned out and open. Measuring the voltage drop across each, I found the entire ~9V drop across the uppermost LED, so it appeared to be open.

After jumpering across the suspect LED, the other two in the string lit (of course, too brightly relative to their peers), so it was indeed open and the problem.

The right fix would be to replace the broken LED, but I don’t have any white 10mm LEDs on hand, it would take a while to order, frosted 10mm LEDs seem to be more difficult to find (or to find clearly specified as such), and I’d have to wade through long lists of nearly-identical products searching for the one that was actually right.

Immediately I thought of a way I could fix it using materials I had on hand — drill a hole into the back of the 10mm LED and sink a white 5mm LED into it. This idea made me cackle with glee, so you can imagine my disappointment upon realizing I don’t in fact have any white 5mm LEDs here. I need to get me some so I can go back and try that yet.

Really, this hack is just as good, though. (Ah, I realize I’m using the word “good” in a perhaps somewhat nontraditional sense.) The SMT LED soldered across the dead 10mm LED’s pins diffused nicely through the 10mm LED lens.

There was also one lonely dark LED in the “E.” Turned out when it failed, it didn’t open, so it was still passing current through for its friends.

I used the same hack on this one, although I did clip one lead off so that the dead LED wouldn’t pull the voltage drop too low for my SMT LED.

I was surprised at how well the hacked LED in the “M” matched the brightness and color of the other white LEDs, given how different its physical construction is. The one in the “E” is a little more noticeable (picture down below), but probably not objectionable if you’re not specifically looking for it. And I’d say a replacement 10mm LED has fairly good odds of being a little off in color or brightness, too.

At 5mA I should have nothing to worry about; but I watched the first SMT LED with my infrared thermometer for a minute with the power on, and it didn’t get above ambient temperature. Should last a good long time.

“Fixing” the Power Switch

I got the pull-chain switch out of its housing and couldn’t see why it didn’t work. Since my wife said the owner leaves the sign on all the time anyway, I don’t reckon it’s worth replacing the switch, so I removed it and soldered in a bypass wire.

Because the switch was broken in the “on” setting, I could have left it installed and the sign would be on. But the switch is already broken, and who knows when it’ll further break “off” instead of “on.” Under the circumstances, I’d rather bypass it now than have to go back and reopen the case to replace the switch later.

There’s a sizeable cutout in the bottom edge of the back cover for the switch, so it wasn’t really an option to leave the switch cover off. It does look a little odd having the cover on there with no switch protruding, but it’s not awful.

Putting It All Together

And thar she be, in all her working glory. For the moment, anyway.

Shortly after taking that picture, I moved the sign and a couple of blue LEDs on the border went out; then one of them came back on. Half an hour later, both (all) were back on. I’m not sure I’ve seen the end of this yet, and I may have a sizeable job cleaning leads and resoldering cold joints sometime in my future.

Physical Construction

One last thing: the frame and skin construction of the sign forms a rudimentary torsion box. The plastic face and back are quite flimsy by themselves, and even the face with frame glued on was flexing as I was moving it. But the moment I got the back skin screwed on, the entire assembly was quite rigid and immune to flexing and racking. Pretty impressive for such a simple technique.

Posted in Hacks, Inside, Repairs | 3 Comments »

Repairing Roomba Scheduler

Tuesday, January 20th, 2009

Over the holidays, I tried to fix my Roomba Scheduler. I ended up deciding not to try to trace from the battery connector to locate what part had shorted/burned when I connected a rebuilt battery with reverse polarity, I found an eBay seller with remanufactured main boards, and I ordered one for $20.

Yesterday I had time to swap it out and get Roomba working again.

Board Replacement

I had the new board completely mounted and half the connectors wired up when I noticed the first problem:

My Roomba has two dirt detectors, and J9 has two rows of pins, one row to each piezo assembly. The refurbed MB had a single-row J9, apparently from an earlier model with a single dirt detector.

I debated a bit about contacting the seller, but decided it was a waste of his time and mine to ask for a replacement board when I had everything I needed already at hand. I desoldered J9 from my original board (tedious heat-tug-heat-tug-heat-tug that demonstrates how good J9′s plastic is because it didn’t melt and how good the PCB is because the only thing I ruined was one of the test points), and had a much easier time desoldering the single-row J9 from the new board.

Then I got frustrated trying to get the solder out of the through holes. I had some success adding solder to the holes and applying solder wick, but there were three holes I just couldn’t get. Finally I gave up and pulled out the PCB drill bit set — a #68 bit spun gently by hand turns out to be just the ticket for cleaning the solder out of these holes. (Never again will I try to wick solder out of empty holes.)

I cleaned the two-row jack’s leads with a wire brush, soldered it in, took a picture from an angle that looks like I still have the single-row jack in the board, and reassembled Roomba.

Attempt #1

I was delighted to see it turn on when I pressed the power button. I knew that should be what would happen, but it was still gratifying to see it actually happen.

Prematurely. Gratifying.

I took it to the living room to vacuum, hit Clean, and it just burped. It burped when I hit any button. Grrrr.

Diagnostics and Cliff Sensors

The first page I found when searching for why it was “burping” was What is Roomba saying to me?, which says that the “eh” sound means there’s a faulty cliff sensor.

I relocated the Roomba Discovery models’ diagnostic tests page and ran through the individual sensor diagnostics. On test 2, outer cliff sensors, only the starboard-most sensor worked properly; the outer port sensor showed “cliff” all the time. On test 3, both inner sensors showed “cliff” all the time.

Gathering more test materials and retesting, I found that only the outer starboard sensor’s IR LED was lighting my infrared sensor card (apparently no longer sold at Radio Shack, but apparently formerly part number 276-099 and/or 276-1099), and the cliff-sensor IR LEDs were dark. Further, shining the virtual wall’s IR LED beacon into the cliff sensors caused the diagnostic LEDs to flicker, indicating that the cliff-sensor IR detectors (phototransistors or photodiodes) were working properly, so the problem definitely seemed to be in the LEDs.

All three of the dark LEDs individually checked good with the diode tester on my multimeter. Tracing the cliff sensors’ LEDs, I found that the three dark ones were all powered in a single series circuit, fed by the red (anode) and orange (cathode) wires in the top row of J24 at the port end of the main board.

My meter’s diode tester didn’t use a high enough voltage to overcome the forward voltage drop of the series string, so I hooked my bench power supply to a 1KΩ resistor and the series chain. All the LEDs now glowed on my IR sensor card, so the LEDs weren’t faulty (which I had assumed anyway) — the problem was with the driver.

Robot Reviews Forum and Q4 LED Driver

Searching online for advice, I quickly found this forum post titled “Cliff sensor failure apart from one” complaining of exactly the same problem. “Gordon,” a very knowledgeable contributor, indicated that the dark LEDs were all driven by the same transistor, Q4.

I found Q4 on the board and it was twisted, so I straightened it without particularly thinking. (This fact isn’t relevant yet. Just wait.)

Gordon indicated which MB test points correspond to which Q4 pins, provided an apparently reverse-engineered and incredibly helpful schematic of the cliff-sensor LED drive system, and indicated that the Q4 and Q37 bases should have a 1kHz square wave on them, with a corresponding signal on the collectors.

I put the scope on Q4 and its base was oscillating nicely, but its collector stayed high. This made me suspect a faulty Q4, so I quickly and cleanly desoldered it and checked it in my out-of-circuit transistor tester. The tester said it was good with a β of about 220, which wasn’t what I wanted to see. I wanted it to be broken.

And then while I was straightening the leads and pondering what to do next, the emitter leg felt loose and I pulled it out with my fingers. Removed, it looked rather like a dessicated cricket leg you’d find in a corner.

I don’t have SS8050s on hand (that I know of), but they’re all over the MB and appear to be used as general-purpose transistors. I found a 2N3904 with the same pinout in my parts bin (if you think all TO-92 transistors with the same part number have the same pinout, you haven’t shopped enough different manufacturers), tested about the same β, installed it, and the IR LEDs all glowed.

I could have pulled an SS8050 from my original MB, but (1) I wanted to keep it intact, and (2) I wanted to demonstrate that another transistor would work. And so it did!

Sweet, Sweet Success

Roomba powered up again, but this time it didn’t burp (I mean “eh”) when I hit buttons, and it went straight into cleaning mode. Woo-hoo! I took it to the living room and let it clean, and it ran the course and picked up all the cat hair.

Today I emailed the eBay seller just to let him know what had happened. I wasn’t upset and I left him all positive feedback because the board he sold me fixed my problems within my abilities, plus I may have broken Q4 myself while straightening it, plus I had some fun tracing the problem. But I thought he should know what happened so he could check future boards more carefully for customers less fascinated by the process of repair.

He replied:

wow, yes you went above and beyond what I would expect. Thanks for helping out, i’m sorry you had to do so much.

sounds like the glass is half full with you.

There may be some truth to that.

Posted in Repairs, Roomba | 9 Comments »

Replacing a Dead Arduino FTDI USB-Serial Chip

Monday, January 19th, 2009

During the installation of “Organic Energy Cloud”, right after one of my fly wires turned bright red and dripped off the breadboard, I stopped being able to upload programs to the Arduino. As it was five minutes before the gallery opening, I didn’t want to take the time to replace the Arduino with a spare (that I’d had the foresight to bring along); and the Arduino was still operating with the last program I had loaded, which fortunately was sending a random twinkling pattern to the LEDs.

So I left it be and made a mental note to check it out later. Since the ATmega was still working but I had no communication with the board, I already had a guess that the FTDI FT232RL USB-serial chip was burned out. And I happened to have one on hand that I had ordered for testing LED puck USB control — which has been waiting for a year and can afford to wait a little longer.

Diagnostics

I hooked it up this morning and found that the TX and RX LEDs stay on solid (which my CoolPix doesn’t capture well) — not a good sign.

And the IDE’s serial port selection menu doesn’t list the USB serial connection as an option, further confirmation that the FTDI chip is toasty.

Removal

Removing SMT chips would be a great job for a hot air pencil. Since I don’t have one, I blobbed solder across all the leads on one side, then heated the solder mass with the iron while gently prying up that edge of the chip. It came up quickly and with little resistance, and I repeated the trick on the other side, then mopped up the excess solder with solder wick and brushed off the inevitable flux with rubbing alcohol.

I pulled the pads for pins 27 and 28 completely off the board, but they were unconnected and are for an optional 12MHz external oscillator not used in this design. I also noted the bridge between pads 25 and 26, but it appears to be by design — the pins are both tied to ground anyway, 25 being AGND and 26 being TEST that must be tied to ground for normal operation.

Replacement

I tried using the blob-and-drag method to solder the new chip in place, but ended up using the SparkFun blob-and-wick method instead.

After cleaning the flux again, the resulting board looks pretty reasonable (although I managed to get the chip on crooked, dang it). And the serial lights aren’t solid any more,

and the board now shows up in the list of connection, and I can download programs to it again. Hoo-rah!

Posted in Arduino, Repairs | 10 Comments »

Fixing a Buzzing Clock Radio

Wednesday, December 31st, 2008

I’ve been using this clock radio for at least twenty-three years, and I love being able to read its huge 2″ digits when I wake up during the night and my eyes are blurry and unfocused. It’s having a little trouble here competing with the sunlight streaming in the side window, but it’s nice and bright at night when I need it.

Lately it’s picked up an annoying habit of buzzing at, you guessed it, 60Hz. The intensity and timbre of the buzz vary, sometimes coming and going at the same time I can hear the furnace fan starting up and shutting down, sometimes apparently at random.

Listening carefully has led me to believe that the buzz isn’t coming from the speaker end of the clock, but rather from the power supply end. Speaker buzz would suggest bad filter capacitors (and one could certainly forgive twenty-five-year-old electrolytics for needing to be replaced); but power supply buzz makes me think of transformer windings coming loose and needing to be re-epoxied, metal brackets near the transformer working loose and needing to be tightened, and that sort of thing.

Today I had time to open it up and — I think — fix the problem.

Most of that is radio circuitry, and I don’t even use the radio. The clock part appears to be two ICs underneath the raised pushbutton circuit board. The transformer is in the “basement level” between the two posts to the left of the display’s ribbon cable.

Right away I could see something I suspected was at least part of the problem. The transformer’s forward mounting tab was bent at other than the proper 90° angle from the body, only one edge of the mounting screw’s head was in contact with the tab, and there was a lot of slack between the tab and the mounting boss.

After removing the main PCB to make room to get a screwdriver in there and straightening the mounting tab with pliers, I got the screw tightened down properly. I could tell that the screw hadn’t worked loose over time but had been assembled this way at the factory: I could feel that I was tapping new threads into the mounting boss as I turned. Expecting the plastic to be fairly brittle after twenty-plus years, I worked gingerly, and successfully tightened the screw without breaking the plastic.

While turning the screw, the entire end of the transformer’s cover was rocking from side to side, and a different angle revealed the reason and a second likely suspect for the buzzing sound (of which I carefully took this out-of-focus picture). The mounting cover had an edge bent out away from the laminated core and a loose tab.

After a little work tightening things with pliers and pressure, the cover seemed to be pretty well fastened. I checked the power supply electrolytics with my Capacitor Wizard since I had the clock open anyway, and they all tested good. I reassembled the clock, retesting for buzz several times along the way, and so far the buzz appears to have been banished.

The transformer problem was clearly a manufacturing defect; and it’s interesting to think that it took over twenty years to manifest itself. Here’s to the next twenty!

Posted in Inside, Repairs | 4 Comments »

Cleaning (and Cleaning . . . and Cleaning) Akai Headrush E2

Wednesday, December 31st, 2008

I just bought an Akai Headrush E2 delay and looping effects pedal. It’s the box that the amazing KT Tunstall uses in her solo performances of “Black Horse and the Cherry Tree” to lay down her own rhythm and backing vocals before playing guitar and singing, all by herself. It’s a really slick setup.

I got a great deal on eBay — they retail for ~$200 and typically run about $150 on eBay, but I picked mine up for $76 missing the 9V power supply. It turned out to be an even better deal than I imagined, because the seller forgot to mention that the pedal came with a generous helping of organic matter, lovingly applied all over the pedal. This picture is after a preliminary 3x cleaning with Goo-Gone.

Not only was the case unsightly, but the foot switch action was dodgy as well, and that’s not easily cleaned from the outside. To really get the case clean, I wanted to get the panel loose of the controls so I could give it a good soak; to fix the buttons, I wanted to spray them with contact cleaner. I figured I may as well show off the inside while I had it open anyway.

There’s the upper PC board. Note the filth that crept down onto the mode select pushbutton, and even the potentiometers:

I had already got the outside of the lower case fairly clean, but wanted to clean the inside as well, so I went ahead and took both boards out. Here’s the lower PCB, where all the magic happens:

I actually had a plan for dealing with the filth. Goo-Gone is great at softening and removing sticky adhesives like the remains of the world’s largest velcro strip the former owner had attached to the bottom of the pedal; but there’s no cleaner like Fantastik for removing the evils that men have done from arcade game control panels and (apparently) guitar/keyboard effects boxes.

I gave the top case about a ten-minute soak in Fantastik — I had already soaked and scrubbed in Goo-Gone three times, mind — and after the soak it literally rinsed completely clean under the faucet, with the tiny exception of a little bit of gunk still in one of the potentiometer mounting recesses. The foot switches left behind a pool of brown liquid (and I had only sprayed the mounting threads), the potentiometer knobs had white inset lines again, and the washers that I’d had to pry loose of the case with my knife were clean and shiny.

I also used an “acid brush” (dry, no cleaner) to knock the accumulated dust and grit loose of the PC boards around the base of every component that penetrates the top cover and get the boards nice and clean again.

The pushbutton foot switches aren’t quite sealed, and I was pretty sure I could see in to the inside along the solder lugs. I sprayed with wiper cleaner/lubricant, worked the switches a bunch of times, and repeated the spray/work process twice more. Shiny!

Same pedal reassembled about an hour later, with towel lint added for your viewing pleasure.

And remember, folks, you can’t go around calling yourself anal-retentive if you don’t bother to align your fasteners.

The pedal now works perfectly — no more double-taps from switch bounce and missed taps from stickiness, etc.

It makes such a difference that before cleaning, I couldn’t understand the operating instructions (because the pedal didn’t seem to be doing what they seemed to be saying), and afterward they’re much more clear (although incomplete in failing to mention that it does not record while you’re tapping the tempo in delay mode, pity; and confusing, incomplete, and inaccurate in their description of looping mode operation; but who, bitter, me?).

Seriously, after an order of magnitude shorter time poking around than I had already done before cleaning, I feel pretty comfortable that I understand how to get it to do the things I want to do. Using the delay mode, I can now play a pretty passable rendition of the “Fly Like an Eagle” synthesizer intro. Wonder what to tackle next . . .

Posted in Equipment, Inside, Repairs | 41 Comments »

Trying to Repair Roomba Scheduler

Monday, December 29th, 2008

About two and a half years ago, I did something foolish in trusting the wiring instructions from a Roomba battery rebuild supplier and blew up my brand new Roomba Scheduler. Hasn’t worked since, because I wanted to see if I could find the problem and fix it myself before sending it back for factory service. Turns out I can’t (or at least haven’t), but the inside is interesting nevertheless.

Opening

Getting into the Scheduler is easier than getting into the first generation, mainly because it (almost) all comes apart with screws, instead of the (few) latching tabs in the original Roomba. These instructions on fixing the Roomba Discovery “Circle Dance” do a good job of showing the screw locations, although the site then goes on to describe processes specific to cleaning the wheels’ optical sensors that weren’t relevant to my problem.

The most important part that wasn’t obvious to me from the instructions is that the front bumper holds down the front edge of the top, so you must remove the bumper, even if you don’t need to work on the bumper area.

Guts and Wiring

Once the cover is off, the inside looks pretty tidy. As on the original Roomba, there’s one main board sandwiched between the battery compartment and the brush deck, and all the sensors and motors cable up to it.

I had to pull all the cables before I could get the board out, and most of the cables had only one place they’d logically plug back in, but I still took pictures to make sure I’d know how to put it back together again, shown here for the convenience of all the king’s horses and all the king’s men who might be trying this themselves at home.

Having removed all the cables, there’s still an optointerruptor at each end with a bumper lever latched into it. It took some prying to get those loose — port (left when in motion, right when facing it to work on it) side first, then pull the board itself loose of the starboard side.

Main Board

And here’s my main board, with nothing that I can see wrong. No scorched components,

no scorched traces. Foo. (The battery connector is J7 on the solder side, in case you want to trace out from there and try to debug this for me.)

With the component spacing so tight on the board, and no obviously damaged components to investigate first, I didn’t feel like bothering to plug all the connections back in and trace battery voltage while the board was out of its little home. So I gave up (for now, anyway), contacted iRobot to ask about repair, and reassembled the Scheduler.

Reassembly

The most noteworthy thing about reassembly is getting the bumper’s port-end (I think) mounting bosses back into their mating holes. Do those first, then the starboard (I think) end of the bumper, then ease the rest of the port end the rest of the way on. Whichever end it is, do the posts first.

Dirt Sensors

The last thing to mention while we’re in here anyway is the dirt detectors. The second or third generation of Roomba introduced dirt detectors that are supposed to be able to tell when Roomba is actually picking up dirt, so it can spend more time vacuuming that area. I think my dirt typically has a fairly uniform distribution on my floor; but maybe some folks like to send Roomba out to clean up knocked-over flowerpots and whatnot.

Anyway, I’ve always wondered how it could tell when there was dirt — some fancy-schmancy optical sensor pointing at the floor??? — and here’s the answer.

Piezo sensors. Dead simple. Dirt hits them, ting-ting pting tang, and they translate the sound / force into an electrical signal that the Roomba interprets as the influx of dirt. Brilliant!

iRobot promises to respond to a customer inquiry within one business day of receipt, so . . . they’re late. But we’ll see what they say about repair service and cost. I understand they also sometimes have returns and refurbs available for purchase; and at the right price, that could get me a new Scheduler and leave me a spare for parts.

Hm, looks like entire used Schedulers are running ~$100 on eBay, and I just found someone selling the circuit boards for $20 plus shipping. I can’t imagine iRobot touching that price for a factory repair, so it looks like I may be able to do this myself after all. Maybe get a spare Scheduler just for the fun of it, too.

Posted in Inside, Repairs, Roomba | 6 Comments »

Fixed a USB Thumb Drive (Sort Of)

Friday, October 3rd, 2008

A couple of weeks ago, Matt from the desktop support group at work asked me for soldering advice / demonstration. Someone he supports kept all her data on a USB thumb drive with no backup, and it stopped working. When he opened it, he found the crystal had come off the board, and he wondered whether I could solder wires to it well enough to get the drive working and retrieve the data before discarding the drive.

It turns out the crystal was a through-hole design that had had its legs crimped into flat strips, then bent out sideways to surface-mount. (You can see the pads where it was originally mounted.) But that created stress points at the end of the crimped area where the leads were bent, and the owner treated the drive roughly enough (I think attached to her keychain that she dropped onto the counter every night) that both legs sheared clear off.

Didn’t leave me much to solder to, either, but I got it done. Matt’s too young to know wire wrap and didn’t have any on hand, but I found some stranded wire and used a single strand. It wasn’t an elegant job, but it was sturdy enough to survive some handling, and it actually worked. In spite of his professed faith in my abilities, Matt was amazed and delighted when he plugged in the drive and the contents popped right up on his computer.

And I get to keep the repaired drive as my reward. Which naturally means that I’ve already broken one of the wires.

Posted in Hacks, Repairs | 6 Comments »

Free UPS + Free Batteries == Hammond Organ

Saturday, September 27th, 2008

UPS that someone gave me because it didn’t work:

Minus its original batteries, apparently slightly past their prime, which I had to pry out of the case by levering with a big screwdriver:

Plus three-year-old unused batteries from the campus fire chief:

Equals I can play my “new” Hammond organ, which is temporarily in storage where there’s no electricity:

Worth noting:

Cold Start
When the UPS is off and there is no utility power, it is possible to cold start the UPS to power the loads from the UPS’s battery.
Note: Cold start is not a normal condition.
Press and hold the on/test button until the UPS begins beeping.
Release the on/test button during the beeping to start the UPS.

Addendum 29-Sep-2008:

Runtime with a 15W wall wart plugged in was about an hour. Runtime with the Hammond plugged in (after fully recharging) was about three minutes. I guess free batteries are worth what you pay for them . . . but I do now know that the UPS works and is worth replacing the batteries.

Posted in Hacks, Repairs | 3 Comments »

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