heathyoung wrote:Ouch. LED's working (backlight) just means that there is current flowing through the voltage regulator. (prereg prior to the 5V reg)
V+ to 5V means you probably dumped your pack voltage (minus led drop) across the microcontroller. They short internally when you subject them to this kind of punishment, so the backlight will work just fine, just nothing else will.
Its probably screwed dude... If you are lucky, it just took out the 5V reg. Maybe.
heathyoung wrote:Yep its probably your 5V reg thats shorted to ground, when you remove it, you will get the pre-reg not running so hot (pre-reg is 12V IIRC?).
At least the micro (pic16f690) isn't dead.
You may also have killed the tantalum capacitor as well. They short and will show similar symptoms. Throw a multimeter across the tantalum and see if it is shorted.
The opamp (that scales the current) not sure where it gets its supply from, if it is using the preregulated (12V) output, is probably not getting the correct voltages and is having a brainfart - dunno if it is rail-rail or not (in which case it would be running off the +5V rail (thats how I designed mine).
dnmun wrote:what is the part number on the 3 terminal regulator that had the melting solder? your external supply is going through that and overheating it. you should replace that regulator i bet, but not sure.
heathyoung wrote:The black thing that is melting the solder isn't a regulator, its a power mosfet being used in its linear region as an amplifier for a zener regulator. Its being overloaded with a load on its output, which is most likely the 5V regulator. Tantalum measures fine at 800 ohms.
The 5V reg is a 3 terminal device (small) 7805 or something like that. Higher resolution photos would help a bit in identifying it, but it should be close (follow the tracks) to the positive side of the tantalum cap.
heathyoung wrote:Looking at the picture, I would say it is the component marked as U3. The 5 legged bugger next to the tantalum cap. The pinout fits (SOT23-5) exactly.
How much current were you drawing on the 5V rail? And on the Vbatt side?
Stupid conformal coating makes it hard to read component values. I like the sticker over the micro prior to conformal coating - beats sandng the chip numbers off I bet
Farnell (element 14) have them in stock for $0.70 each...
http://au.element14.com/micrel-semicond ... tt=MIC5205
dnmun wrote:you can just cut the 5V leg open on the op amp. no need to unsolder it to test it. you need sharp dikes that will be narrow enuff to get in there. cut it midway so you can solder the leg back together later if it is not the culprit.
or if you have a soldering iron now you can heat up the pad and leg until the solder melts and pull the leg up with a small pick.
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