LM2671: Trouble with no output

At first glance I do not see anything wrong with the schematic.

I assume you checked the 12Vout and got zero volts.

The waveform at the SW pin should be monitored with a 'scope to see if any switching action is going on.

Check to be sure you have the correct components in the correct place.

Send us a snapshot of you pcb layout.

I'll grab an oscope capture in the morning and reply again.

I cannot find any evidence of switching with a 300MHz oscilloscope.

Although your layout is not optimal, it should not prevent the regulator for functioning.

I assume that there is a ground plane connected all of the grounds.

I would try to pull up the EN to VIN with a 10k resistor and see if the regulator starts.

If not, then I would try replacing the regulator.

Thanks for the advice so far. I replaced U16 and started to see switching. Now the output is too low ~2.75 VDC instead of 12VDC. I attached a plot of VSW for your review. The input power is 24VDC at 11mA.

I am curious about the FB resistors. I verified that they match the design, but when connected to Pin 8, the 909 ohms measures 854 Ohms and the 8.25k Ohms measures 1680 Ohms. This is with no power applied. Could this be why the output is low?

I think that measureing the resistor in circuit is not accurate.  You will have to remove them to be sure.

Be sure that your output cap is rated fo 12V.  And the Schottky diode is rated for the full input voltage.

Check to be sure that there is no unexpected heavy load on the output that could drag down Vout.

As I mentioned your layout needs improvement.  Specifically the grounds of the input caps, diode and output caps

need to be as close as possible together.  This may be upsetting the operation.  Try to follow the layout example in the

data sheet as closely as possible.

I would try using heavy wire to connect the grounds of the above mentioned components.

And connecting the bottom FB resistor to near the ground of the IC.  And see if that helps.