jim rozen wrote:

In article , Jeff Wisnia says...

Robert Swinney wrote:

So Jim, what are the electronics for? I sorta figured the new LEDs used
(only) appropriate dropping resistors like older conventional LEDs.


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.


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



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

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"