iMac 21.5 2017 4K no image on internal screen

[iMuhtaseb]

820-00597

iMac 21.5" A1418 2017 4K is not showing an image properly.. It shows an image externally without issues but to the internal screen it's intermittent.

Another screen results the same thing, it's a main logic board issue.

I had doubts about the LVDS connector so I replaced it, still the same issue..

The main logic board diagnostics LEDs are 5.. #1, #2, #3 works OK but #4 is half on and #5 is off.. I don't know what #4 means while it's not completely off or completely on..

Anybody having an idea or seen this case prior?

[iMuhtaseb]

Re: iMac 21.5 2017 4K no image on internal screen

I measured the MOSFET next the LED #4 and here are the measurements:

Q0304
1 = GND
2 = DP LINK OK = 0.0V
3 = GFX OK DRN = 0.0V
4 = GND
5 = GFX OK = 3.3 V
6 = GFX OK K = 1.2V

DP_LINK_OK being missing makes the LED #4 dims lightly as the schematics says (attachment below).. I traced back DP_LINK_OK source and it's U8800.. the AMD Radeon graphics card..

This is mind boggling, think it's something fixable? What should be my next step?

[iMuhtaseb]

Re: iMac 21.5 2017 4K no image on internal screen

My two main suspects are currently:
U2032
U2033
And I've replaced them, without success...

I also replaced U4500 (CBTL06142EEE); mux chip
without success