Can you modify the code so that the heart beat section sends a byte out=20 the UART when it turns the LED on? That would allow you to confirm the=20 UART is initialized and at the correct baud rate. Are you using auto=20 baud detect? Kerry David Duffy (AVD) wrote: > ivp wrote: > =20 >>> I guess the only other thing I can try before replacing the PIC is >>> to add some debugging pin code, maybe to the UART ISR for >>> starters >>> =20 >>> =20 >> How about disconnecting the receiver until the PIC has stabilised, >> or something like that. Might help identify where the problem really >> is >> =20 >> =20 > I'll give that a go tomorrow. The receiver output is full of random=20 > noise when idle, but it is the same on all boards. > > As for power, there's not much to the circuit. A 12V battery via a=20 > 1N4007, into a 78L05 with a 100uF on the input. > > What's really odd about this is that replacing the chip fixed the=20 > problem on the first faulty unit. Apart from those two units, all the=20 > others work well. > > I'd bet money that replacing the PIC will solve the problem, but I'd=20 > really like to know why before I do that. Since it is a TQFP package,=20 > swapping them back and forth not an option. > > I do have brown-out detect enabled IIRC. The only other idea I have is=20 > that the power-up timer is bad on some chips. Seems unlikely though. > David... > > =20 --=20 Internal Virus Database is out-of-date. Checked by AVG Anti-Virus. Version: 7.0.289 / Virus Database: 267.11.13 - Release Date: 10/6/05 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .