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Sorry for stupid questions, but are you using a series or AT cut crystal?
Proper loading caps?
Ray



On Sun, 7 Mar 2010 19:30:35 -0800 (PST), yamanoor sairam wrote:
>=A0Dear All,
>=A0I developed a basic board to help people learn PIC microcontroller
>=A0programming. The board is based on the PIC 16F877A microcontroller
>=A0and I have enclosed a picture of the board at the following page:
>=A0http://mechatronicscraze.wordpress.com/2010/02/08/the-board-has-
>=A0been-populated-and-it-is-ready/
>=A0The board was tested and the results were successful. I ordered for
>=A0another set of 10 boards and populated four of them. I faced a
>=A0weird problem with three boards. I identified that in one of the
>=A0boards, the board didn't work because of a low quality tact switch
>=A0that kept my MCLR pin low. I avoided soldering the tact switches in
>=A0the other two boards. In both these boards, I see that the MCLR pin
>=A0is high and the voltage is 5V between pin 11 and 12 of 16F877A.
>=A0However, both the boards were not functional. On replacement of the
>=A0crystals and capacitors, one of the board has started functioning.
>=A0The other board is not functional even after replacing three sets
>=A0of capacitors and crystals of both XT and HS frequencies. I have
>=A0taken care that I have set the correct fuse bit before I build my
>=A0program. (XT or HS at address 2007 and low voltage programming was
>=A0disabled)
>=A0The problem is that I don't have an access to oscilloscope and I am
>=A0not able to identify the problem behind the board. I am very sure
>=A0that someone might have faced this problem. I would be glad if
>=A0anyone could offer me assistance for the same.
>
>=A0Sairam





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