I'm on a university vehicle competition team, and we inherited a set of hardware that we didn't design. I've been trying to figure out what's wrong with a certain piece of the circuit, and I was hoping you guys could help me out.
We have an ATMega48 with some sensors attached, which use the analog-digital converter to measure voltage and current (via Hall Effect sensors). The problem is, the circuitry to provide the reference voltage isn't outputting nearly the correct voltage. It uses resistors and a Zener diode to step 3.3 volts down to 2.5; but the pin is only seeing about 0.7 volts. The schematic is attached. Sorry that it's a little messy, but the diode in question is U9.
I doubt the actual design of the circuitry is at fault, but I don't know what the most likely places it would fail are. I tried replacing the diode and checking the resistors; both seem to be okay. How likely is it that the diode was damaged when it was soldered?
The software, by the way, seems to confirm the fact that the voltage reference is too low -- the ADC maxes out at a much lower voltage than it should, and the current sensors are reading 0x03FF when they're only outputting 1.4 volts.
Any thoughts as to where the failure might be?