ivp wrote:
>> The PIC has a 10K resistor from MCLR to Vdd, but no capacitor
>> to Vss. If I reset it by shorting to Vss, the unit works fine again.
>> It's only when the board is first powered up that the fault occurs
>>    =20
>
> If you change nothing else, a cap would ensure that Vdd gets up
> before /mclr, holding the chip in reset. However, PWRTE is meant
> to perform that task
>  =20

Only had time for two tests today.

The first was to add a 100n capacitor (also tried 10n & 1u) to the MCLR=20
line. Faulty unit still does not function correctly when powered-up. If=20
I shorted that cap (pulled MCLR low) momentarily, it did start working=20
correctly.

The second test was to remove the 47u capacitor on the 5V rail. Same as=20
above; still faulty operation on start-up.

For kicks, I checked the markings on the PIC chip from a good and bad=20
unit; they are from the same batch as far as I can tell.

I guess the only other thing I can try before replacing the PIC is to=20
add some debugging pin code, maybe to the UART ISR for starters.
David...

--=20
___________________________________________
David Duffy        Audio Visual Devices P/L
Unit 8, 10 Hook St, Capalaba 4157 Australia
Ph: +61 7 38235717      Fax: +61 7 38234717
Our Web Site: www.audiovisualdevices.com.au
___________________________________________

--=20
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