Can someone tell me what kind of diode this is?
Hello biuro,
It is RS1K, Fast Recovery Diodes, 800V, 1A, SMA/DO-214AC
RS1A-RS1K.pdf (81,8 КБ)
Thank you very much Adam7 
Hi biuro,
Based on the size differential of the part you ordered and the part on the board, it looks like the part on the board is an SMC (DO-214AB) package.
Therefore, your part is likely the RS3K-E3/9AT.
From the RS3K datasheet:
If you find that your part is not as large as the SMC package, then it would likely be an SMB (DO-214AA) package, and the part would then likely be the RS2K-E3/52T
