Electronic component identification and sourcing
It appears to be a SMCJ78CA Bidirectional Transient Suppression Diode, if that makes any sense for your board.  These parts are available from all the big distributors, approx £0.50/unit at 1-off.

Board shows D1, D2, D3 but no apparent polarity markings.

Datasheets below show same part numbers for right-looking package, labelled BGT, which are diodes which don't need polarity markings.  My guess is that "425" is the date code.


https://www.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_smcj_datasheet.pdf.pdf
https://www.diodes.com/assets/Datasheets/ds19003.pdf


Eg Littelfuse datasheet shows part numbers and marking for the unidirectional and bidirectional 78V diodes:


Don't follow my guess blindly!