They are the PV diodes and rated at 1 amp and probably susceptible to age failure. Make the DC for the various other Power Supplies on the board.
Way back I saved a few with getting out the one bad diode, but a real pain and not always successful. I also (once) separate boards and then reattached via jumper wires just to test, and it was not successful.
Under the rectifier you will find a rev code for the boards, you might want to work on the K, they were the last and best board. G