I have come to the conclusion that the RF board in the TS-850 is toast. After several repairs, it’s still deaf as a post. There has obviously been some damage to the components on the bottom of the board near the signal entry point from the antenna – at least. I don’t know what else might be damaged. I’ve looked for a replacement. I find a number of boards on eBay, but about 2/3 of them show the exact same sort of burns in the same area of the board, so I would expect them to be bad as well.
At this point I’m shelving the project. After an extended absence from ham radio I’m not even entirely sure I’ll want to get back on the air. From what I can tell, there doesn’t seem to be nearly the amount of non-contest CW traffic that there once was. I have no interest in contest style exchanges of nothing but call signs and bogus signal reports for POTA, SOTA, or whatever QSO party is going on. I haven’t seen any PSK31. RTTY might be interesting, but FT8 is of no interest to me. If I’m getting on the air, it’s to rag chew or at least have a little human to human interaction with the radio as the means, not the end, and preferably no computer required. I’ll get on the air with my FT-817ND and the old Heathkit HW-16 and see whether I want to pursue fixing the 850 or getting something more modern.