The 151 LEDs and the left flipper are both controlled by the node 8 board--as is a bunch of other stuff mostly on the lower playfield. Node 8 controls both lower flippers and both slings. A lot of stuff might behave unexpectedly if that board had an 'event'. The boards are black so it is harder to see burned parts but I would look there for evidence of the source of the burning smell.
Node 8 board is under the playfield next to the left flipper. It is a long-ish rectangular board with a bunch of connectors. You can't miss it.