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While prepping a V3 uBITX I had already built up to give to a friend of mine, all of a sudden the RF Power output went to ZERO. Thought for sure I'd somehow blown 1 or both of the IRF510's, but I learned (and taught) electronic equipment troubleshooting during the later years of my 20 year US Army career and one point I learned was that nothing is always as it seems.
First thing I checked was voltage to the drains of the IRF510's -- ZERO (yes it was hooked up and turned on). Tracing the voltage back, I had nothing on the supply ends of L8 OR L9. I checked continuity between those same points of L8 and L9 and had good connections there.
I found that I 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 -- poor plating through the hole. I put a piece of 30 gauge wire wrap wire through the via and soldered it on both sides. This brought the +12 back to the supply side of L8, L9 and subsequently the drains of the IRF-510's . Put it all back together and I now had full power again.
I've noticed in the past a few people having similar problems and not sure if they ever did find them. This might be the cause and is definitely worth checking as there will be no visible indication of anything bad between the PA Power pin on P1 and the rest of the PA circuit.
Hope this is helpful to some of you.
Jim Sheldon, W0EB