[SOLVED] Debugging a new µC PCB

[oyvdahl]

Hi

We have designed a pcb with an at91sam9xe chip from atmel.
There are two supply voltages: 1.8V and 3.3V. The problem is that the 3.3V supply somehow puts 2.3V on the 1.8V net.
I have disconnected the 1.8V voltage regulator so I am sure that it is not the LD1117AS18 (1.8V regulator) that is the problem.

My guess would be a soldering error somewhere, but I have inspected the board with a microscope and cannot find anything. The microcontroller is a 208-pin PQFP package, so it is too hard to isolate the problem by desoldering some of the pins.

I know this is a long shot and it is pretty much impossible for you guys to say anything about what the error is with so little information. But right now I am a little desperate and therefor I am wondering if anyone could make a wild guess to what is causing 2.4V on the 1.8V line? Or just some debugging approach that you have used with luck in the past?

Best Regards
Oyvind

 

[ckshivaram]

check if the 3.3v regulator shows 2.3v at power on or after some time.. If it is after some time means ,,,, touch all the IC's on the board and see which IC is getting heated up. There is some short in the pCB, or a damaged IC on board that is drawing more current at some stage and causing the voltage to drop.. check the polarity of all the IC mounted.