The internal display of concerned iMac is not being recognized in OSX and doesn't turn on. With an external display connected everything works fine.
Unfortunately I have not managed to find any boardview files for this specific model - thus debugging it is quite painful.
Diagnostic LED 4 does not turn on - when powering on the device and attaching my multimeter to port 1 of U4450 the LED does turn on - have not attempted this with the screen enabled as thats not a fix of any kind. This seems to indicate that VIDEO_ON is somehow not being set to high properly, causing the screen not to toggle itself on.
Some relevant measurements:
Display connector - J4400 measured
1 12,14
2 12,14
3 12,14
4 12,14
5 12,14
6 12,14
7 gnd
8 gnd
9 gnd
10 gnd
11 gnd
12 gnd
13 2,1
14 2,1
15 1,537
16 1,54
17 0,719
18 0,532
19 gnd
20 0,128
21 0,756
22 gnd
23 missing
24 missing
25 gnd
26 missing
27 missing
28 gnd
29 0,76
30 0,537
U4450 measured (http://www.nxp.com/documents/data_sheet/74AUP2G14.pdf)
1 0,765
2 gnd
3 3
4 Short to GND when iMac is powered on
5 3,3
6 3,3
I presume that pin 4 is not supposed to short to ground when power is enabled - the short is not present when board is off. Could this be due to this chip or the active backlighting circuitry (mainly a transistor of some kind and a MOSFET).
I think I need to replace U4450 or Q8101. I have a U4450 component available, but don't want to risk blowing it to pieces if the attached circuitry might be able to destroy it... I have not yet been able to locate Q8101..
Thanks for your help already!
Unfortunately I have not managed to find any boardview files for this specific model - thus debugging it is quite painful.
Diagnostic LED 4 does not turn on - when powering on the device and attaching my multimeter to port 1 of U4450 the LED does turn on - have not attempted this with the screen enabled as thats not a fix of any kind. This seems to indicate that VIDEO_ON is somehow not being set to high properly, causing the screen not to toggle itself on.
Some relevant measurements:
Display connector - J4400 measured
1 12,14
2 12,14
3 12,14
4 12,14
5 12,14
6 12,14
7 gnd
8 gnd
9 gnd
10 gnd
11 gnd
12 gnd
13 2,1
14 2,1
15 1,537
16 1,54
17 0,719
18 0,532
19 gnd
20 0,128
21 0,756
22 gnd
23 missing
24 missing
25 gnd
26 missing
27 missing
28 gnd
29 0,76
30 0,537
U4450 measured (http://www.nxp.com/documents/data_sheet/74AUP2G14.pdf)
1 0,765
2 gnd
3 3
4 Short to GND when iMac is powered on
5 3,3
6 3,3
I presume that pin 4 is not supposed to short to ground when power is enabled - the short is not present when board is off. Could this be due to this chip or the active backlighting circuitry (mainly a transistor of some kind and a MOSFET).
I think I need to replace U4450 or Q8101. I have a U4450 component available, but don't want to risk blowing it to pieces if the attached circuitry might be able to destroy it... I have not yet been able to locate Q8101..
Thanks for your help already!
Last edited: