Interesting, lesser spotted problem with 2019 27-inch iMac.
iMac boots but there is no backlight on the display. The display image can bee seen under certain viewing angle. After testing the device with a new display it is obvious the issue lies with the logic board rather than with the display.
On 2019 27-inch iMac model, the backlight circuit is located on the logic board itself. Gone are the days where backlight was conveniently located on the separate board that can be easily replaced.
This issue requires iMac logic board repair.
Consulting the boardview software, we have located the backlight fuse. Usually, the fuse only blows due to failure of another component on the board. In this case it was the faulty capacitor that caused the fuse to blow.
Handy tip, you can use iMac 2015 board as a donor for parts, the fuses and capacitors are the same. Same goes for the 5K iMac display, 2015/2017/2019 models share the same display.
After replacing the capacitor and the fuse we have the backlight again.
