Electronic – How to go about debugging PCB Power Supply Circuits to ensure correct output voltage

I've decided that breadboarding ahead of time is a waste of time unless there are aspects of a part's performance that you need to measure yourself.

I even think building the board in pieces is a waste of time. The initial hardware debug just takes a day or two. Any subtle issues won't show up until software integration anyway. I'd rather debug one circuit (the complete one) than several ad-hoc reductions of the circuit.

Just build the thing! Assemble the whole board and power it up. Look at the supply voltage. How many mA does it draw? Which part is burning hot? Which part is warm? Then try to burn firmware on to whatever microcontroller is on the board. Then start writing firmware. Get the clock going and toggle a pin. Get serial (or whatever) communication up. Now write test programs for each peripheral. Then build the production test fixture and start writing the "real" firmware.

Edit:

On finding stuck rails

If a supply rail is stuck to ground, (measures 0 ohms with an ohmmeter), power it up on a bench supply. Set the voltage normally and the current limit to a few hundred mA. Print out the PCB design on paper, and find a DMM that measures microvolts. Measure microvolts starting at the supply terminals, and write down the voltage drops on the PCB printout. By looking at microvolt differences, you can trace exactly where the current is going without depopulating or chopping up the PCB. This technique is a better than using an ohmmeter because you can pump a lot of current through the circuit, more than any normal ohmmeter will supply.

A similar technique works for finding shorted traces on an otherwise populated board. Run the board a use a scope to find "digital" traces that are in an in-between voltage range.

There are trade-offs, as always. Having a regulator on the board board gives you some flexibility in choosing the power source for the circuit, clean regulated voltage, which are good. But it is an additional cost, size, power loss and heating, which are bad.