U22 LM issues

7 pins version,

5 pins lm, two versions, one always gives out 5v,
the second has only 5v out during startup.

Note, the LM 5 pins (LM2596) is only active when the pin 5 (on / off) 0 to max 1.6v dc has.
At a higher voltage the LM is not active.

If the pin is not connected, usually with a cap to ground.
Then the LM is always active.

LM 7 pins (LM2599),
When the SD /SS pin 7 voltage is between 0V and 1.3V, the regulator is in shutdown, the output voltage is zero.

With the SD /SS pin 7 voltage between approximately 1.3V and 1.8V,
the internal regulator circuitry is operating.

When the SD /SS pin 7 voltage is between 1.8V and 2.8V, the regulator is in a Soft-start condition.

Note: LM2599S-5.0, If you disable pin 7 from the motherboard it become active.
When active the voltage are,

Pin,
1-12v
2-5v
3-5v
4-0v (Ground)
5-1.7v
6-5v
7-between 5/7v

(Thank you to Johnny_B for publishing it)

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