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I have an A1708 - 820-00875-A, that has no signs of liquid contact, pulls 19.5V from ampmeter, consumes 0.5A at start and stabilizes at 0.27A, has backlight, but no chime and no image (even on external monitor).
I get voltage on vcore coils, and CPU gets hot.
Sorry for the late reply (a lot of problems to deal with).
It looks that the iGPU its working, because when connected just the board on the bench, without the LCD, it has an image on external monitor. Already tried with a known good lcd and a good lcd cable, but with the same result. With LCD conected it has no image (internal or external monitor). Without internal LCD connected, it has image on external monitor.