Imac black screen, external works fine

[katrienv]

Hello,

I have a problem with my imac.

what have I done:
I have a imac 27" late 2009. I had the famous white screen, so my videocard was broken. I ordered a new one. installed that one, imac works fine. I reïnstalled with Sierra and tested the imac for about a week.

Today I decided that everything works fine so I want to screw back the imac together (some screws inside where not screwed back, so I screwed them together. Connected back the lcd.

But when I start now the imac I have a black screen on my imac.
External monitor works fine but nothing on the 27" screen. I see the ligt of the imac goes on.

When I check in system preferences I see the 27" monitor, I can adjust the brightness (I see the black go more or less dark when I slide the slider). But nothing on the screen.

I have the same imac from my wife. I tested it out with another screen, same result.
I placed back the broken graphics card, but not a white screen, but same black screen.

Anyone an idea what the problem can be?
The connector on the logic board looks ok, nothing special.
smc & nvram allready done, doesn't help.

Any idea?

 

[katrienv]

In case anyone has the same problem. I found it out myself.

On the motherboard there was a problem with transistor Q9001, I resoldered the transistor and problem solved.

 

[PK003]

In case anyone has the same problem. I found it out myself.

On the motherboard there was a problem with transistor Q9001, I resoldered the transistor and problem solved.

Many thanks Katrienv!!

I have been trying to figure out the problem knowing it was not the graphics card, LCD screen, inverter, backlight, HDD, etc. I was narrowing it down and my searches with Google and came across your post. I had no idea where Q9001 was but as I started looking closely at the logic board something out of place came to my attention and when I read the transistor number it matched! I guess because it is located so close to the graphic card tray support arms I must have bumped it when removing the card.

If you look closely at the picture I have popped the top off it it and it has opened up like a hatch or door.
Do you think this is fixable or do I need to replace the entire resistor?

 

[katrienv]

I think it will be fixable without replacing.
Just good soldering skill needed

 

[PK003]

Not sure how to go about soldering it. All three solder joints are still in good order. It's just that the top has popped off. If I was to flip it back over how would I keep it in place or make it all connect again?

 

[katrienv]

the picture is not very clear for me.
When the top has popped off you have to replace the transistor I think

 

[PK003]

the picture is not very clear for me.
When the top has popped off you have to replace the transistor I think

Yeah that's what I am in the process of doing, although, it's a pain trying to find out which 2N7002 diode is used on this logic board.

 

[julll]

Yeah that's what I am in the process of doing, although, it's a pain trying to find out which 2N7002 diode is used on this logic board.

Hi

I narrowed down my black screen issue to a torn out q9001 component as well.
Did you ever find the correct part? Generic? Please share info if you can.
It reads k72 x2 on the diode… Anyone?
Cheers

 

[Nguyen Duc Hieu]

Thank you very much.
This is exactly the same issue with my 2 iMacs late 2009 and 2010.
I'll send it to the repair shop to try.

Knowing the cause and how to fix is will help me bargain with the shop about repair cost.

 

[Nguyen Duc Hieu]

I bought the 2N7002k mosfet (transistor) from the local shop. The mark is the same K72... And brought my iMac to a local cell phone repair shop nearby.
It was a quick fix after knowing the cause and got the necessary component.

https://www.onsemi.com/pdf/datasheet/2n7002k-d.pdf

 

[Radical78]

I took my logic board to get fixed. I changed the LVDS connector (they applied some green stuff that to protect the soldering).

Didn't notice that I busted the Q9001 - 2N7002 Mosfet, while inserting the GPU.

 

[julll]

I bought the 2N7002k mosfet (transistor) from the local shop. The mark is the same K72... And brought my iMac to a local cell phone repair shop nearby.
It was a quick fix after knowing the cause and got the necessary component.

https://www.onsemi.com/pdf/datasheet/2n7002k-d.pdf

Thanks a lot for your reply.
Ordered the same part, did the soldering myself – my first! – and everything works fine again.
Cheers

 

[Nguyen Duc Hieu]

Thanks a lot for your reply.
Ordered the same part, did the soldering myself – my first! – and everything works fine again.
Cheers

Thank to your fine photo, I could find the correct component.
I couldn't take a clear enough photo of my mosfet to show the mark.