Imac 21.5 lcd issue

[jasko_jacker]

When I push the power button I hear the sound but the screen remain black,
only after a few attempts , the screen turns on.
(The HD seems to work even when the screen remains black, and when the lcd is on the pc work well for many hours)
I noticed that on the card that manages the voltage for the lamps (darfon 4h + v2676.081) there is a connector with this signal:
pin 4 GND
pin 3 ENABLE
pin 2 DIM
pin 1 VSYNC
Enable signal is missing when the screen is Black and have 1.6V
when the screen is on.
I have no schematic and I don't understand well this type of hardware and I want to know if the enable is an OUT or IN signal ?

[piernov]

Re: Imac 21.5 lcd issue

Would be nice to know what machine it is…

[rediii]

Re: Imac 21.5 lcd issue

gpu intact?

[jasko_jacker]

Re: Imac 21.5 lcd issue

Would be nice to know what machine it is…

Label is missing but I think the model is Apple iMac 21.5 A1311
The pic is a similar inverter board
I post original pic as soon as possible

[jasko_jacker]

Re: Imac 21.5 lcd issue

gpu intact?

I do not know it personally, but the owner who uses it with windows instead of macos told me that the video card is recognized.

[piernov]

Re: Imac 21.5 lcd issue

There are 4 different models of A1311, only one doesn't have a dedicated graphics card. That's 3 chances out of 4 to have a dead GPU.

[jasko_jacker]

Re: Imac 21.5 lcd issue

I have Only this info without dismantling motherboard, but I see the screws of a videocard rear heatsink.
Can I try a reflow or this type of bga is in the "black list" ?

[KvnTM]

Re: Imac 21.5 lcd issue

It is this one:


NVIDIA GeForce 9400M graphics with 256 MB of shared memory or ATI Radeon HD 4670 graphics with 256 MB of dedicated GDDR3 memory.
Both of them are known to fail. Throw it away and avoid pre 2012 Mac's at all cost.