LED flashlight failure report

My underwater kinetics 2AAA flashlight died. I had it on my keychain, and it took a pretty hard knock I guess when I dropped
the keys the other day.
The SMT inductor broke off its solder pads, and a tiny widget busted off the top of one of the transistors.
I soldered the inductor back on, and after a bit of head scratching I decided that the tall, dark colored, grainy cylidrical thing that was epoxied to the SMT transitor was probably a heatsink. So I simply used 5 minute epoxy to glue it back together at the break.
I also gussied the other SMT devices up with a few dabs of epoxy as well, because the original dabs were a bit on the spare side.
Jim
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So Jim, what are the electronics for? I sorta figured the new LEDs used (only) appropriate dropping resistors like older conventional LEDs.
Bob Swinney

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Robert Swinney wrote:

Likely it's a dc to dc converter of some sort, much more efficient than wasting power in a dropping resistor. I'm amazed at the kind of efficiencies I see claimed in chip manufacturer's ads these days.
Jim just confirmed what I've been saying for the last ten years or so, repair of consumer electronics has become more of a mechanical job than an electronic troubleshooting one. The parts themselves hardly ever fail these days, it's mainly "loose disconnections" that keep the parts from doing their intended tasks.
Jeff
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The electronics are two transistors, a couple of resistors, and a flyback inductor, to boost the voltage so that a white LED that takes four volts to turn on, can be run off of two AAA batteries that only make three volts.
Now if I only could have found the loose connection that made my daughter's cell phone stop working - not that I didn't inspect every bit of the board under a microscope for an hour or so!
Jim
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jim rozen wrote:

Deja vu all over again Jim. My youngest (17 year old) son sat on or whacked the stuubby little antenna on his two month old Motorola camera phone (which I'd just bought him to replace the previous phone which he lost somewhere.) and it twisted over in the plastic threads of the housing so that it's inside end scrubbed several tiny surface mount parts right off the board.
Because our cellphone carrier (Cingular) is no longer doing any service work on phones at their stores here in Taxachusetts, sick phones have to be mailed in for repair, so I figured there was no chance I could FTF sweet talk a local repair guy into doing me a favor and fixing it on the sly. The mail-in service operation wanted $150 to exchange a "damaged" phone. (Yeah, I know, I should have sprung for the "all risk" insurance Cingular wanted to sell me, but I must have been projecting my cautious experience and not thinking about the kid's, so I declined it.)
I couldn't Google up anything in the way of a print for the phone, and I figured I'd go nuts trying to reverse engineer it and then obtain the components it needed, so I just pulled the SIM card out of it, chucked the phone in the trash, and bought the kid a rugged, non-flip, internal antenna ex-Cingular Nokia complete with wall and car chargers for $30 on eBay.
Stuck the SIM card into it, made a quick phone call to Conversent so they could plug the phone's ID numbers into their computer, and he was on the air again. He can bloody well live with a plebian phone until he's on his own - Ha!
(It's times like this when I think children are G-d's punishment for having sex.)
Jeff
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On Mon, 06 Dec 2004 13:02:53 -0500, Jeff Wisnia

You had some doubts??????
Gunner
"To be civilized is to restrain the ability to commit mayhem. To be incapable of committing mayhem is not the mark of the civilized, merely the domesticated." - Trefor Thomas
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Yep! Like Jeff said, some sort of a DC to DC thingie. Comments regarding mechanical repair to modern electronics reminds me: RCA Colortrack TV receiver - mid '80s model. Modularized; a problem tracked down to the tuner control module - opened up tuner control module and found a note under the shield that the "new" set had already been serviced before it was sold to me. The pecker tracks therein must have been the first fix for an "intermittent" in the module because it came clear (again) when I reinstalled it.
Some time later, when the problem reappeared I was able to fix it with a popsicle stick propped under the rear of the tuner control module. Now this was "really cool" - complex electronic problem fixed with a popsicle stick!
Over the years, the module would exhibit the same problem which was handily repaired via the popsicle stick fix. Ultimately, a stack of popsicle sticks failed to clear the problem - like it was still intermittent, over a cycle of months, or sometimes years.
Optovisor (finally) to the rescue revealed a tiny PCB crack around an edge card connector on the front of the module. This was 4 or 5 years ago. After soldering over the crack, the old RCA has given trouble-free service as a bedroom set ever since.
Bob Swinney
Jeff Wisnia says...

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Jim - know the direction of hit - then look at the massive object - how the gravity does stuff. Might be a break in the pcb due to a pull... Mechanical fit that isn't mated directly...
Martin
jim rozen wrote:

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Eastburn says...

Ah, it's a moot point now.
Last night I mentioned to my wife that I had fixed the flashlight.
"Oh, what went wrong with it?"
"Some of the parts had come off the circuit board, and I was eminently clever and managed to fix it. Damn I'm smart."
Or some other kind of preening to that effect.
I proceeded to unscrew the lens to show her what a great microelectronics handyman I really am.
The lens flipped out of my fingers as it screwed off the barrel of the light, and flipped across the room. Because I tracked it closely as it spun across the floor, I found it right away under the kitchen table.
The circuit board, with LED attached, had come loose and flew off in some other direction.
Correction: some other *dimension*. It's gone now, I can say that for sure after seaching for an hour. After looking high and low, I finally decided that it must have dropped down into the hole in the kitchen floor where there had been an old heating pipe at one time.
So I went down the basement and peered up onto the top of the beam that was right under the hole. Yep, there was something there. With the aid of an inspection mirror and a (different) flashlight I extracted the object.
Dumbfounded, I held an adapter that I had made years ago, to fit PR-style flashlight bulbs into antique navy battle lanterns, which take DC bayonette lamps. I'm sure I must have looked for *that* thing for a few hours, ten years ago.
Maybe in ten years I'll be looking for something else and find that LED on its board. In the meantime I think I'll plug that damn hole up.
Jim
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Martin H.

gravity
I was told to expect days like that, but no one warned me that they'd all be that way!
Harold
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"lost" items. Some found, some not. Was working on a 76 Chevy pickup of mine one time, rebuilding carb - disconnected the two throttle return springs (one inside the other) = *never* did find them. sigh. Ken.
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On Tue, 07 Dec 2004 22:27:43 GMT, Ken Sterling (Ken Sterling) wrote:

"As physicists now know, there is some nonzero probability that any object will, through quantum effects, tunnel from the workbench in your shop to Floyds Knobs, Indiana (unless your shop is already in Indiana, in which case the object will tunnel to Trotters, North Dakota). The smaller mass of the object, the higher the probability. Therefore, disassembled parts, particularly small ones, of machines disappear much faster than assembled machines." Greg Dermer: rec.crafts.metalworking
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Yep. That's exactly what happened. If any of you kind folk happen to find my LED flashlight innards, please give a holler.
Thank you.
Jim
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    Glad to -- if you will only post a link to an image of the innards, so we know what they look like. :-)
    Good Luck,         DoN.
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On 7 Dec 2004 20:27:58 -0500, snipped-for-privacy@d-and-d.com (DoN. Nichols) wrote:

So THAT's what went crunch when Icame down the cellar steps tonight. The little critter made it all the way to Waterloo Ontario (it was a tiny peice of PC board with a couple funny electronic parts on it - and the cat had been playing with it)
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wrote:

A LONG time ago (as will be seen) I dropped a small, irreplaceable part. As all fumble-fingers must do, I had trained myself to freeze and listen carefully at the first hint of dropping something: dead silence. I looked everywhere that might have muffled the sound of a small part landing and rolling away, but couldn't find it. Later, I found the part in my pant cuff. (When was the last time you wore trousers with permanent cuffs? For me it must have been late '50s or early '60s.)

Don't do that; you will never have the impetus of losing something else down the hole to cause you to find the LED.
-- --Pete
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snip----]
(When

Ha! I don't recall when that was. The first thing I did with work pants in "the good old days" was to remove the cuff. Those suckers can hold one hell of a lot of chips, not just irreplaceable parts!
H
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Thanx, Jeff! I shoulda known.
Bob Swinney

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Jeff Wisnia wrote:

More than likely it was a FET in a constant Current mode driver. So the 'resistance' of the FET constantly changes as the battery depletes giving the same light output until there is not enough control or battery.
One concern with the 5 minute - it might be to hot and hurt semiconductor.
Martin
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Resistors waste power. The best way to get a lot of light out of LEDs is to pulse them at a relatively high rate putting lots of current through them. I've designed a flashing red LED beacon for a client (it's used in an alarm system) that puts 250 mA through two strings of LEDs (0.5 A total) . They are pulsed at 35 kHz using a small, very cheap microcontroller (25c in quantity) with the power stored in an inductor being switched across them with a MOSFET. Current taken from the supply is < 10 mA. The whole thing is on a tiny 30 mm by 45 mm PCB using mostly surface mount parts.
Leon
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