The STMicroelectronics SMAJ70A-TR is a unidirectional TRANSIL™ TVS diode in the SMAJ series, built for general-purpose transient suppression. It's a Zener-type device, not a signal diode — the scorch mark on a dead board tells you the clamping junction took the hit. The key numbers for fit: 70V reverse standoff (the rail it protects), 77.8V minimum breakdown (where it starts conducting), and 146V maximum clamping at Ipp (the voltage the downstream silicon sees). If your 70V rail sees transients that stay under 146V, this part keeps the rest of the board alive.
Package and temperature — where it lives on the board
Housed in a DO-214AC (SMA) package, surface-mount only. The SMA footprint is common and easy to rework with hot air — no underfill needed. No power line protection (it's unidirectional), so keep it on signal or low-voltage DC rails.