While playing the other night, the upper (back end of pf) GI string went out. All GI fuses are fine (checked with multi-meter). I checked all TIP102s and none are shorted open. I tried unplugging and replugging the GI connectors. No luck. D25 and D27 are already hard wired with 18 gauge (diode removed) and the connection is good.

Obviously I must be missing something. Can anyone help?

Thanks guys. Ended up being the diode that Williams later figured out should be hardwired instead. Two of the GI strings (D25, D27) were already modded this way but one that wasn't had a cold solder joint. Hard wired it. Back in action.