Help identifying diode

Trying to repair display/electronics card in Miele microwave oven,
cirka 1990 (it's custom built into kitchen panel, so I prefer keeping
it if it's possible).

I have this shorted diode, it's part of the power supply to the card:

http://www.lindell.se/diode1.jpg
http://www.lindell.se/diode2.jpg
http://www.lindell.se/diode3.jpg

It has plastic body, 5 mm length.

The label: A12 J 9H
And the "J" is 50% larger than the other characters.

I have spent hours on google trying to identify it and/or finding an
equivalent, but no luck.
No circuit diagram, and I'm not skilled enough to determine it's
function, could be a Zener diode.

So please, any tips on how to identify it are welcome!

Regards,
Jonatan Lindell

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