Diode ss54 should be fine at 8.4v? Buck Driver help needed

LightRider , SORRY for misleading you in your attempt to repair your driver , but myself I was mislead by the lay down of the driver and considered that the 3 pin device with the sense resistor was a fet transistor... I DO APOLOGIZE !!!

Loneocean , you are the HERO of this ! Respect , you are good ! My hat down !...Patience and science , you are an invaluable asset for this forum .THANK YOU !

Maybe I can wash my sin with this : The U4 is a " ZXTC 1009 " - current sense monitor , you can find it on Google.

Sorry again , LightRider , it seems that I'm getting old and obsolete...