I'm trying to use an op-amp in an amplifier circuit (the LM324N), but it doesn't seem to be working properly. From a 5V power supply, I measured the non-inverting input at 2.5V, the inverting input at 0.8V and the output at 3.9V. Shouldn't the output be at the full 5V? I haven't used op-amps much, so it might just be a simple mistake with the circuit, which I'll attach later.