[SOLVED]Help with PIC18F2550 soldered (sometimes it work, sometime it doesn't)

Thread Starter


Joined Jan 15, 2010
I would really appreciate if you can tell me any idea you get by the following situation. (I really need help :( )

I have soldered a socket to a board, and put a 18F2550 in it. I have also soldered a circuit in it in which I use pin RB0~RB4. I also soldered RB6,7 to connect to the programmer. I have soldered other necessary components.

The program I wrote basically gives 1s or 0s to pins B0 to B4. nothing else.

I have successfully program the PIC.

Then when I power the PIC sometimes it works, sometimes it doesn't. If it works it keeps working good until turn off (there is no unstability)

When it doesnt, a small push in the side of the PIC makes it work. Investigating more, when it does not work a touch with a metal to the PIN B5 makes it work. if it is working it makes it not work again!!!

Now I suspect about the soldering. however here is the strange and bewildering fact:

I used a oscilloscope to test the PINs directly.(Not the soldered connections) Pin Vdd is receiving 5V successfully. However Pins B0 to B4 are not outputing anything!
If I touch B5 they start.
So It is not the soldering or the connections!!!

What is happening here? Any idea?
I have run out of possible solutions! :(
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Thread Starter


Joined Jan 15, 2010
Is the /MCLR pin connected or floating?
it is pull up.

I ve read that the problem might be pin B5 connected to nothing and me not disabling LVP in the code.
I ll try this today.

EDIT: I tried this on a breadboard and the same thing happens. So it is not a matter of soldering...

When I connect a LED resistor circuit to B5, it does not work of course (as I post in my other thread) but the problem of this thread does not happen.
So it is a B5 pin problem...sigh

EDIT2 :It was never a matter of soldering. it turns put that B5 sometimes causes this behavior (reset). So you have to explicitly disable LVP in your code.

In my case

#pragma config LVP = OFF
and voila! problem solved
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