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AvMap EPF IV GPS - 12V power - trying to identify damaged diodes (?)


Jan 23, 2018
Jan 23, 2018
Please be gentle first time here.

Hands up stupid, who whilst distracted reversed the supply polarity on a aviation GPS unit (me raises hand)
The result was that smell we all know well of semiconductors frying. The unit remains operational but on battery power only (6xNiMH AA) It will not function power-up on 12V.

The usual supply is external 10-36V DC. The unit is also designed to trickle charge the back-up NiMHs

Image attached>IMG_20180121_151425559.jpg

To components to the right of the power plug below the screw are heat damaged. They are both 2 pin semi conductors with the following markings
(ON) 621 36B
(ON) 620 939B

I believe the first one (621) is a Schottky Diode like this
Maybe the second is another Schottky but I can't find any meaningful references to the number despite lots of searching.
Any ideas or help here appreciated.?

The group of black wires (centre photo) comes from the battery NiMH back looks like 7 supply/charge connections and a common. It sound like the schottkys purpose is to allow isolation between the 12V external and internal battery supplies. I also wonder if I could simply jumper-out my two damaged components and remove the batteries which I don't really need. Thoughts here appreciated also?

Thank you all.