I got this two days ago also.

Here are my stats:

PIC18F242 in SOIC-28 config
20mHz operation

2 regulators, 7812 feeding 7805.  7812 used for op-amp configuration
with TC7660 to make -12VDC supply also.

Current draw when chip operates correctly (entire board) 48mA (about 30
mA when PIC removed).
Current draw when chip is "torched"... 0.78A (at 24VDC input).

I can't think that I did too much to it.  I did have some external
inputs connected to the board (through opto-isolation chips) without
power connected to PIC for a short time.  Everything was on static mat,
but I was rushing this design through though.

This seemed VERY strange to me, I've never destroyed a chip before
either.  I replaced the chip and everything works fine.

Anyone know if this happens "in the field" as it were?  These are being
used in a hydraulic man-lift and I don't want to be replacing these
every week.

DD

On Sat, 2003-12-13 at 10:52, John J. McDonough wrote:
> Last night I was working on the PIC-EL board
> (http://www.amqrp.org/elmer160/board) and rather suddenly I could no longer
> program the PIC.  Now, I had been soldering/desoldering and generally
> mangling things, so I suspected perhaps I got something unglued.  In poking
> around, I burned myself on the regulator.
>
> OK, this experiment I've run before.  7805's will valiantly try to pump out
> 5 volts into a direct short, getting astonishingly hot in the process, but
> the programming LED would still light, so I had some 5 volts there. More
> poking around and I realized the PIC was getting pretty hot, too.  Pulled
> out the PIC, board draws reasonable current and nothing gets hot.  Well,
> maybe I somehow dislodged the short.
>
> Put the PIC back in, everything still gets hot.  Put the scope on the
> crystal lines, and no oscillation.  OK, pull the PIC back out, check the
> voltages at each pin, they all make sense.  Put the scope on each pin, too,
> in case something else on the board is oscillating, but they all draw
> straight lines.
>
> In desparation, I plug in another PIC, everything works just dandy.  Put the
> old one back in and nothing but heat.  I've abused a lot of PICs, many much
> worse than this one, and was never able to damage one.  Not sure what
> happened to this one, but now it's able to draw a bunch of current and get
> quite toasty in the process.  Quite a surprise.
>
> One more for the experience log, and very glad that the parts drawer is
> relatively deep in PICs.
>
> 72/73 de WB8RCR    http://www.qsl.net/wb8rcr
> didileydadidah     QRP-L #1446 Code Warriors #35
>
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--
Dan Devine

"Serving the public since....well, never"

dannyboy259@comcast.net

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