I fixed it with the help of my dealer.
I pulled the 500PS out of the Fraim and removed the Burndies.
I removed six screws from the bottom using a metric allen set.
Bottom500PSDR by sc-sld
It was easy to slide out the unit from the case and the switch side came out first.
Switch by sc-sld
Then with the end of a knife I spread the brass spring so that it was not overly compressed. You can see the small brass spring on the left. See below for the compressed spring. I did not get a picture of the uncompressed spring but you can easily imagine and you can check it before you put it back together.
SwitchCloseUP by sc-sld
Bingo. All good.
The biggest problem by far was getting the 500PS out of the Fraim and unlocking the Burndies. The rest was a breeze. You only slide the power supply out of the case by a couple of inches to get to the spring. Many thanks to Dale G. at Serious HiFi for the coaching.