I see nothing other than a cap on the backplane. The part no. is 691-PCB1-0B1 Rev B. This is in a circa 2001 Atlas SD35.
It had:
DCDR, R2LC07, and RS3 board (sticker says RS25D25.
I installed:
Cruse Commander M, and a Lionel 691R2LCC08 (R2LC / RADIO RECEIVER (C08 CODE)). RailSounds and RS Power board unchanged.