2120 HSS command will not engage forward or reverse

[Ford850]

Here's a link to some of the Hitachi diode marking codes. Scroll down a little and the blue markings with dots are shown. Maybe that will help ID the specs on the diode and the part number. The diameter measurement should determine the final part, but it looks like its either U17E or V17E if the lines are blue and the dots are black). HITACHI(2) - MARKING CODE @wiki - アットウィキ
https://img.atwikiimg.com/www21.atwiki.jp/mcmaster/attach/349/710/U17E_01.jpg
https://img.atwikiimg.com/www21.atwiki.jp/mcmaster/attach/349/711/V17E_01.jpg

 

[grcutter]

I think that the diode may be the Hitachi V19E. The U17E and V17E diodes mentioned above are Avalanche Diodes that are designed to limit the voltage in the 400v range. I don't think that anything on this control board reaches that voltage.

Here is the datasheet for the V19E: http://www.hitachi-power-semiconductor-device.co.jp/en/products/diode/pdf/pde-v19-2.pdf

Here is a list of places that may stock it: V19E Hitachi datasheet C1S3172338524 | Octopart

 

[grcutter]

A very late update to this thread: The V19E that I mentioned in the post above is not correct and is too small.
I think that Ford850 is correct, the original diode is the Hitachi U17E.
The U17E is now obsolete and is quite difficult to obtain. There are places that sell it for ~$10 each but they have a 10 piece minimum order or more.
I had ordered the the U19E which is about $2 each with a 5 piece minimum and tried it in my controller and found that it works as well.
The diode is the first component in the path from the power lead. So if the diode goes bad, the controller loses power.
It seems that any general purpose diode that has specs similar to the Hitachi U17E or U19E would also serve as a good substitute.