880M internal display issue nikey(bios) imac 2009 EMC2429

[kingbacana]

Good afternoon macrumor community,


I have a question about the startup sequence of a IMAC.

First I explain what happend.

1. I have a imac with a ati 4850 512mb card, which works perfectly fine.
2. I harvested a 880M from a laptop and flashed this with a bios version that support apple.
3. I replaced the videocard and got external display using mini dp.
   It can run games and the 880M is recongized and works.

But Internal display is not working with this new card. I put the ati 4850 back and the internal works again. so the cable and display is fine. psu is fine too.



Does somebody knows whats the diffrence between the ati 4850 and 880M with startup, could it be that the 880M is not sending the right signals?

I measured the voltage on the 14 pin psu connector all seems fine. Except pin 13 for enable backlight always is 0.00v to 1v.

If I solder a wire from a 3.3v source to the pin 13 will it work?



I think maybe the 880M doesnt send a signal for enableing backlight and startup video using the lvds connector I have no clue or the display and videocard together draw to much current together? But external works, but external is ofcourse a diffrent power soucrce for its display.



Does someone have a clue??

My last resort is soldering wires to generate/ force signals. But I have read in other macbook pro that people did this and killed the logic board because sometimes signals only need to be a second there..

also its very hard to test because when the display is in, I cannot measure voltage, is here a smart trick for?