I guess it's time, I purchased my PL400 new in 1972, build date 42nd week of 72, S/N 17, Edmonds, WA. It's been a faithful amp with only one problem about a year after I got it. Something failed and it trashed a set of Bose 901 speakers. I have to give it to PL as they repaired no charge as did Bose. So it's WOPL time, hope to get another 20 years out of it. Unfortunately my PL400 uses the Argonne meters not the later Jewell ones so I can't use the WO Light Board Kit. Here is a picture of my control board, it doesn't match any schematic I have found, must have been an early short run board.