Thanks to info from Leif, KC8RWR, about the purpose of the chip that was heating up on my Arduino board (an LM386 used to determine which socket was supplying voltage for the board) I decided to try just taking the hot chip off the board. This afternoon I fired up my reflow station and blew some 466 degree F air on that chip. It came right off and the Arduino appears to work just fine without it.
This was only a semi-satisfying repair. It would have been much better if I'd really known what I was doing, and if I'd really known what was going on with that chip.
The removed chip is up by the tip of the pen (TOO SMALL!). The transistor and the relay that keys the transmitter are on a piece of PC board above the Arduino.
That Arduino called CQ for me on 20 meters tonight -- Mel, K4JFF, in Georgia responded. Thanks Leif! And thanks again to Mark, K6HX, for the code.
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20
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Good doings. I got one on order. The CWTD sessions convinced me. Plus one of my choreographer colleagues uses them for shows (they call 'em "dance recitals" in the parlance)...
ReplyDeleteWithout that opamp you may have problems to power the board from USB, because it drives a FET switching the USB power to the board if the external power is not applied.
ReplyDeleteThe other half of the opamp is used to drive the indicator LED on the board - that's why you have lost that capability.
I think the chip just gave up the ghost and has a short internally.
You can find the schematics here:
Arduino Uno schematics
Alternatively, you may have a short on the output of that opamp, overloading it (therefore it gets hot). That would mean the FET is likely blown, the LED has 1k resistor in series, so it wouldn't cause issues.
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