The 8000hd psu test often remains difficult because you run the risk that you damage the motherboard.

Now I figured out a solution to test the psu, externally.

It is a no-load test, so not a complete test.
But you're able to check the psu reasonable before you connect it to the motherboard.

Do it at your own risk, and use your mind during the repair.
Repairing the psu is not suitable for someone with a low technical knowledge.
There are Hazards, as high voltage risks.

But good luck with the repairs.

(Thank you to Johnny_B for publishing it)

All the best about hardware/support from Johnny_B, link :
http://jb8a8f8.com
http://jb8a8f8.nl