Maybe I played too much with the RF board?
Posted: 06 May 2023, 11:42
After about 30 years, I took the soldering iron back on an RF project. In recent years I have designed and implemented many electronic projects, but not in the RF field. I ordered the (tr)uSDX kit from Up Tech Store (Aliexpress) and started. I was very excited to make my first HF transceiver with my own hands. I followed Manuel's procedure for adjusting the notch filters using a nanoVNA with no problems. Everything worked, but I wasn't able to get more than 2.5W on each band. I tried to add or remove one or more turns from the toroids with no success. I suspected one or more of the mosfets was faulty and as I had some spare BS170, I replaced them all. I made a little progress - a maximum of 3.5W, and in one case almost 3W at 75% efficiency - but no more. It seemed enough to me, but since I was testing, I had soldered the mosfets with long leads. I decided to shorten them. From that moment on, I couldn't get the board to work again: all the mosfets gone, one way or another, especially Q1. Actually, even the very first mosfet mounted in Q1 position was getting very hot during TX tests, even when I pressed PTT for just one or two seconds. Tried to replace them multiple times, frying them each time. I consider myself pretty good at soldering, so I don't think I've broken mosfets with heat, at least not all the times. I also always used a good 50 ohm dummy load during tests. Yesterday I turned on the device one more time: never touched the PTT, but the two mosfets left on the board suddenly burst and smoke came out, presumably from the other side of the RF board. Is it possible that I damaged the PCB so much to make some short circuits between tracks near the mosfets? Or maybe I misplaced the fets? I'm giving up, but I'm still grateful for the time spent assembling the kit. I suppose I have a lesson to learn from this story, but what is it?
73 de Giuseppe
73 de Giuseppe