@HectorNavarroMX

I have the problem with 3rd light on a iMac A1418 EMC 2889. It can be resolved with a reflow on gpu? i would be better a reballing. But at this moment i can’t afford this, so. Is it fixable with a reflow?

Needs a new replacement. It's too hard too replace. I’ve see similar repairs on YouTube about TouchID flex for iPhone. It needs a stencil, solder station, flux, fine tips, wire and UV glue to avoid short circuit.

Sometimes it would be hard to diagnose. The worst scenario is a failure on your logic board, yeah your second motherboard replacement turns on, but are u sure that all IC involved on charge are working properly? It may be so hard to test, it needs the logic board diagram, scheme file to navigate on chips, equipment to test and replace damaged components by microsoldering.

I had similar problem with a iPhone 8 plus. I can testing it with a baku regulable power source and a sunshine activator cable. This video maybe can help you. How to test and charge iPhone 8+ battery with BAKU 305d power source and sunshine SS-909 cable

I don't have equipment, I have watched a lot of videos on YouTube. It seems a little hard, for the right installation it needs 3 machines, for remove display, for align and glue screen and touch, and bubble remover. Another diy technique or machine only demostrates a bad quality repair. (They are on refurbish industry, they are on YouTube as rewa) For me, is more affordable to buy a full display assembly because my repair shop is small and does not have iPhone x everyday.