issue seems to be power related, but only power to the back light

I have a 2010 27” iMac.  My issue seems to be power related, but only power to the back light. Putting the display to sleep and waking it will fix but only for a moment. It’s as if the display backlight is being turned off by code or power to the inverter is shorting. (I replaced the inverter board without success.)

When this started, first middle brightness went then highest brightness months later and now currently only low brightness works, but works fine. Sometimes high brightness even works, but rarely. If the screen goes black, which it does within three seconds at high brightness i can wake with the sleep trick.

Thoughts? @oldturkey03 or @mayer