Just to give you an update, we found that the firing board was not operating correctly so we changed it out. We also replaced the wire that runs from the SCR firing board to the snubber circuit as this is the one that was discolored and burned from what seemed to be an overheating problem as well as the SCR's in that phase. There had been some current problems as the SCR's showed signs of pitting on the surfaces and this also was apparent on the heatsinks. We resurfaced the heatsinks and installed the new SCR's.
The contractor went to the jobsite and reported back the the contactor (bypass) looked fine and that the contacts are as new. We are going to the site tomorrow to do a start-up on the unit. I will report further about this.