Tx power dropped to 0.02W. SWR fine 1.5-1.8

[M7TAW]

I was using cat control over USB for 20m FT8, I also had a 12v power supply 1A. I was running the board for about an hour. Flicking between FT8 and WSPR, getting about 1.5W out registering on the board display with ~1.8swr when Txing.

I then noticed all of sudden that the board was showing 0.02W on Tx with 1.8SWR. I tried removing the power supply and running usb only but same power output.

I've seen suggestions of the MOSFETs being the issue but I took a look at them and no obvious signs of burning out. Would they be obviously damaged?

[LILO]

1.5W with 12V supply? That is too low. Looks like your rf board is out of tune. And that could be the cause of FETs death.

Damaged transistors can look like new wo visible damage. Use DMM to check.

[M7TAW]

Apologies it was actually a 9V plug. Does that sound more reasonable for original power output?

Excuse my novice electronics skills, but what should I be looking for with the fets specifically on the DMM? what mode and what pins etc?

[M7TAW]

So I think I'm supposed to be checking the drain pin versus the source. I think following a tutorial online they seem ok? Is the pinout DGS if you're facing the flat side for these BS170?

[LILO]

SD should look like diode. DS, GS, GD nothing.
And probably you have to desolder L15 to isolate transistors from the rest of the circuit.

And the first thing I'd do is to check output power with external equipment.