imac 21.5 2009 820-2494-A black screen

[lincev]

Hi all, now i have this problem...

This imac has full black screen. i can see a screen get power but black screen
Board has all 4 LED on.
I replaced the Graphic card, Screen, LCD power board, LCD cable, Main power board with known working parts, but still the same. So I asume this is a board issue as other than the board I have replaced everything to check.

with external monitor i have image and i can install macOSX catalina without problems, can work ethernet, usb, wifi, all parts.

any ideas? thanks for all

 

[2informaticos]

Any history fault available?
Missing both image and backlight for sure?

Do you get voltage at pins 28 &29 of J9002?

Check continuity for all coils and resistors in "LCD MUX & CHOKES" page from schematic.

 

[lincev]

any problem, always ok

only image, I have backlight

pin28= 3,3v (with image in external monitor)
ping29= 3,3v (same)

yes I have continuity in R8900,01,02....57 but I don't have in L8904 and L8954 (is normal) thanks

 

[2informaticos]

Change L8904/54 then; or bypass them with tiny wires.

 

[lincev]

hi again, I change this and now I have continuity but I don't have image...

 

[2informaticos]

Check again all components in that page.
Don't forget R8980/1 and RP8980.
Also check continuity for all lines until video connector.

 

[lincev]

I check this again R8980/1 continuity perfect

RP8980 i don't have this item

 

[2informaticos]

Didn't find it in boardview?

 

[lincev]

sorry I don't understand u, in Boardview right

and i have this continuity of pics

 

[2informaticos]

"RP8980 i don't have this item"
You can't locate it on the board, or is ripped off?

 

[lincev]

I sent you a photo of the part of the board so that you could see it yourself, I think that this version of the board does not have those components

The computer was working fine until the graphics card broke. That's why I think that this version of the board doesn't need that component.

 

[lincev]

Excuse me, I have been able to see another motherboard of this model and if you have them, but it is the version with graphics included (without card slot)

 

[2informaticos]

"I sent you a photo of the part of the board so that you could see it yourself"
As per boardview, RP8980 is not in that area; just few centimeters away.
The boardview I'm looking at, has the MXM connector.

 

[lincev]

omg !! 8980 ... In my head I had 8900... a thousand apologies I'm very stupid

 

[lincev]

ok friend yes I have continuity in all points 3,4 with U8750 and J9002 and points 1,2 with R8980/1

 

[2informaticos]

Did you check if all mentioned resistors and coils have internal continuity?

 

[lincev]

yes all right, I check again