Ground voltage problem

[gsg]

Hi

I'm using a 7805 to power a dsPIC33 controller PCB. I've built the 7805 circuit separately on a breadboard. It gives an exact 5v o/p on the breadboard but when i connect ground pin of the controller PCB to it the output goes to around 3.5v and then starts reducing slowly. It means that the ground pin is giving some voltage.

I have checked the PIC board for connectivity and changed all the capacitors. How can I debug this circuit?

PS- the PIC board contains a 3.3v regulator (LE33CD),and rs232 port, two MAX3096 ICs and four isocoupler ICs.

Please help.

 

[karesz]

Hi,
I think you have not only the GND from your breadbord connected to the DSPIC system, but the 5V out to the 3.3V PIC supplying too.
Check it pls, it must have some (maybe "illegal" connection, and so exists eventually a "back(or over)powering" ...
If yopu have only(!) GND connection these effect is inpossible to have.
K.

 

[bobcat1]

Hi

It is look like a current consumption problem (probably a short some ware) or a up-said down connected capacitor (be aware it can blow...)


All the best

Bobi