Jim Sheldon, W0EB, while prepping a V3 uBITX, he had already built up to give to a friend, all of a sudden observed the RF Power output went to ZERO.
He thought for sure that he’d somehow blown one or both of the IRF510’s, but nothing is always as it seems.
He checked voltage to the drains of the IRF510’s — ZERO (yes it was hooked up and turned on). Tracing the voltage back, he had nothing on the supply ends of L8 OR L9. He checked continuity between those same points of L8 and L9 and had good connections there.
He found that he had +12V on the PA Power pin of P1 but nothing on the supply end of L8 which gets connected by a short trace to a very small VIA through the board and a short trace to L8 on the underside. Looking at the underside, the trace was not burned but it turns out that tiny little VIA was open — possibly from poor plating through the hole.
He put a piece of 30 gauge wire wrap wire through the via and soldered it on both sides. This brought the +12v back to the supply side of L8, L9 and subsequently the drains of the IRF-510’s . After putting it all back together again he now had full power restored.
A few people have observed similar problems with loss of power. This might be the cause in these cases as well, and is definitely worth checking. There will be no visible indication of anything bad between the PA Power pin on P1 and the rest of the PA circuit.