On 25-Nov-10 13:24, David Duffy (AVD) wrote:
> ivp wrote:
>>> 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
>>>
>>
>> How about disconnecting the receiver until the PIC has stabilised,
>> or something like that. Might help identify where the problem really
>> is
>>
> I'll give that a go tomorrow. The receiver output is full of random
> 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
> 1N4007, into a 78L05 with a 100uF on the input.
>
> What's really odd about this is that replacing the chip fixed the
> problem on the first faulty unit. Apart from those two units, all the
> others work well.
>
> I'd bet money that replacing the PIC will solve the problem, but I'd
> really like to know why before I do that. Since it is a TQFP package,
> swapping them back and forth not an option.
>
> I do have brown-out detect enabled IIRC. The only other idea I have is
> that the power-up timer is bad on some chips. Seems unlikely though.
> David...
>

Are you clearing all registers at the beginning of the program? The bad=20
PICs could power up with some inconvenient RAM value that you forgot to=20
initialize.

If not that, try to connect the PIC TX line to a PC and transmit back=20
all what you receive. If you don't get good data, use the PC for both TX=20
and RX try again.

Djula
--=20
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