Sorry if this topic has been beaten to death, the forums on this appear to be closed.
I have a UP 1983 SD70ACe (6-28262) I purchased last December (new in the box). The Engine was fine for about 2 weeks then the sound went out. It started to crackle and pop while underway. I have checked the connections, re-seated the RS boards and replaced the RS power board (universal). After replacing the RS power board, all seemed well and the sound was great. This only lasted for about 30 min and then the distortion started up again. There seems to be something going on that is heat related. When the engine sits for awhile, the RS work normal again for a brief period of time. Today I messed around with it and found that only the diesel sounds are going in and out. The sound is still there, but sounds like an AM radio station not quite set on the exact frequency. The horn, bell and crew talk still work fine when the diesel sound go out. What's my next step? Any help most appreciated!
