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[wxsig] RE: T238+ cpu fried?

William Beals will at beals5.com
Sat Jan 12 21:36:35 UTC 2008


(putting this on wxsig as it may be helpful to others)

Ouch!  I'm actually hopeful that your CPU isn't fried though.  They are
amazingly tough buggers and in all my years of playing with them, (and lots
of stupid moves to try and kill them), I have only "succeeded" a few times.

Getting the LCD backlight is a good sign for power being OK, but worth
checking some things a bit later, but first...

First best bet is to unplug everything from the boards except power.  This
minimizes the possibility something external (particularly the 1-wire stuff)
is causing the CPU to not power up correctly.  If, with nothing else plugged
in, you still get no LED flashing or LCD activity, then the problem is
definitely isolated to the board.  If things start working, then you should
be able to quickly isolate what cable is causing the problem.  If your
heartbeat LED is on the main board, having the LCD and button board
unplugged gets you down to bare minimums.

Assuming things are still dead, check the voltage on pins 1, 20, and 31 of
the CPU.  It should be very close to +5V.  If not, then you may have enough
voltage for the backlight, but not enough for the CPU to come up.  An oops
shorting VCC to GND on the CPU side can fry the reset switch as I instigate
a reset by removing power.

Have you messed with P3 at all?  For normal use it shouldn't be used.  If
you have any jumpers on it they can stop the CPU from starting.  Shorting
pins 7 and 8 in particular have the CPU come up in debug mode which looks
very dead unless you have a debugger hooked up.

Check pins 2 and 6 on the MAX232 chip (U1).  Are the roughly +9V and -9V
respectively?  Being off won't necessarily kill the CPU, but will give an
indication of the health of the power systems.

If none of those work, hopefully some of the data gathered above will help
determine some future steps.  Also, if you have an idea what got messed up,
that can give a hint as to what to try next.

If all these fail, the second-last resort is to try and use the debugger
tools to reprogram the CPU in case somehow the flash code got corrupted.
That's pretty involved, so will get to that later if needed. If that doesn't
work then I think I can scrounge up a CPU.  I use them for some other
projects as well, so buy a few extras.


-----Original Message-----
From: John Yost [mailto:k3yjp at yahoo.com] 
Sent: Saturday, January 12, 2008 9:26 AM
To: will at beals5.com
Subject: T238+ cpu


I believe I have cooked my cpu.  The T238 has been
working great for over a year now.  I was attempting
to add the x1w-1 and x1w-2 sensors to the system. 
Have problems getting the barometer to read properly
so have had in on and off many times recalibrating it,
still reads about 20mb high.  

The problem is that on one of the hookup attempts the
jumpers were not set properly and I believe feed some
power back to the t238, cuz the lcd went blank -
backlite with squares instead of text.

I've checked the components and all seem ok.  Just
attempted to reflash the cpu but it is just sitting
there, so no hope there.

So the question is, how much would a programmed cpu
cost, assuming they are still available, and are you
the right person to contact for one?

thanks for the project, wx has never been so much fun
or interesting...and I always liked messing with wx

john K3YJP

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