Two iMacs 2009 - black screen, backlight OK, GPU OK, four LEDs on - any ideas?

[tom.tom]

Hello,

I've recently got two 2009 iMacs (820-2733-A) with the video issue I have never come across before. The symptoms are as described briefly in the topic:

• both boot with chime and load the OS (Live Linux from USB),
• four LEDs are on,
• the LCDs get the backlight, but no video data (black screen with just the backlight),
• no video on the external monitor,
• GPUs are 100% OK,
• LCDs and LVDS cables are 100% OK.

How do I know the listed components are ok - have working 2009 iMac C2D to exchange the components with.

I suspect motherboards, but two iMacs with the same issue? Maybe this is something common for these models and somebody has solved that before?

Any help would be very appreciated.

Thanks in advance.
Tom

[tom.tom]

Re: Two iMacs 2009 - black screen, backlight OK, GPU OK, four LEDs on - any ideas?

One iMac problem solved!

L9000 with infinite resistance was the problem:

[mon2]

Re: Two iMacs 2009 - black screen, backlight OK, GPU OK, four LEDs on - any ideas?

Well done !!

In one case, we had a DIY youtube client (not to knock youtube as we use it often to learn from as well) BUT this guy flex the LVDS cable too much.

This caused a bad interconnect between the display blade connector & the motherboard socket. It was to the point where we had to replace the LVDS connector.

From memory, they are called the ipex connector but double check from pictures and I recall that we paid a premium as the client was in a rush and bought it from Digikey. The quality between the one on the motherboard and the one from DK was night and day. The DK was waaay better and more sturdy. After replacing, video came back perfectly.

Worth a visual inspection of the connector to see if any of the contacts inside the LVDS connector are recessed or not. I posted the full details of this repair somewhere on this forum but can dig for part numbers if you need them. You can send me a PM if you do.

[tom.tom]

Re: Two iMacs 2009 - black screen, backlight OK, GPU OK, four LEDs on - any ideas?

Yeah. One of the first things I did was plugging the LVDS cable to the socked and checkin the connection between the cable lines on the one end of the cable and the socket connectors at the board side where they are soldered.

Repeated that procedure several times unplugging and plugging back the cable.

Once I had the case where I had to replace the LVDS connector but I got the bunch of those cheap ones from Ali.