Replace TR51
Mike
AM mod regulator failure is very common especially with power mics and high power in AM.
I'm using BD250C as replacement. It will last forever.
Sorry for wrong TR number. I could not find schematic for your radio, but I see you figure it out.
Good luck, Mike
A 2SB827 would actually be better than a 2SB817 for the 2985DX, if you can find one, they should be readily available thru RFParts and/or other similar websites. The 2SB827 is slightly higher gain, if memory serves me right.
And yes, it's a direct drop-in. remove the old one, put heat sink compound on the new one, install, solder in, and you might have to re-adjust your AM carrier on your high side down a little. Other than that, it's plug 'n' play.
Cheers!