20" iMac startup, no screen or video output

[nickXedge]

I need some help. I just inherited my father-in-laws broken iMac. He recently had a power surge and now the iMac powers up, you can hear the hard drive spin, but the screen won't come up, doesn't light up at all, however it also doesn't output any video to an external monitor via the mini-DVI adapter.

I don't think it fried the logic board because if it did, the power supply wouldn't transfer power to the hard drive...right?

Any help or suggestions would be helpful. I'm about to crack it open and see if anything looks fried on the inside.

Thanks.

 

[nickXedge]

I think this is the first time I came to MacRumors for help, and I didn't have 5 people jump on a thread...

Alas, I have more information so hopefully someone will find it worth their while to lend a hand.

I popped it open and aside from copious amounts of dust, no obvious damage. I would imagine a surge would physically show in the internals, but evidently not. I cleaned out the dust and checked out the diagnostic LEDs. Here's what I found:

LED 1 - ON
Power supply is recognized. Hooray!

LED 2 - ON
iMac powers on and power supply is not faulty. Hooray!

LED 3 - ON
Video card is communicating with logic board. Hooray!

LED 4 - OFF
****.

From what I found, if LED 4 is off, that means the Video Card is not communicating with the Display Panel. In this case, it is recommended to replace the video card first and if that doesn't solve the problem then replace the panel. It seems in my case it must be the video card, as it will not send output to an external monitor either.

Now, the search begins for a new (or used) video card... once I have one, I'll update this post incase anyone is having a similar issue.

In the meantime, if anyone wants to confirm my findings with their own experiences or anything, please do.

 

[nickXedge]

Welp, I got an ATI Radeon 2600XT on eBay this past Thursday. I figured, if I'm replacing the 2400XT and the 2600XT fits, why not upgrade while I'm at it, especially considering I was able to get a used 2600XT for less than I could find a 2400XT for.

I put it in yesterday and voila, all 4 LEDs lit up and she's back to life. All is well.

If anyone has been reading this and has any questions, I'd be happy to answer them.

 

[RyanShipp]

Same problem by the sounds of it...

Sounds like Ive got one on my workbench with the same issue. No output to the display either directly or output via hdmi. I hear chime, fans and hard drive kick up, and LED 4 is the only one not lighting.

I thought I'd read that LED 4 was for over thermal limit, not video. This gives me some hope though, I was about to start looking for a logic board.

Can you tell me if you had any other symptoms before replacing the video card? Also, any possibility you know where you came across that bit about the 4th LED?

TIA,

RyanShipp

 

[nickXedge]

Ryan,

No other symptoms.

Here is where I found my information on the diagnostic LEDs. Page 204, if it doesn't automatically bring you there.

 

[yarik]

i want to thank OP for posting the whole story. I searched a lot online and many times people would say: "hey, I got it fixed", but leave out the details...

i have the same symptoms and and I ordered also 2600xt. as soon as i will get it, i will put it in the imac and i hope everything will work.

I will post an update.

thanks a lot again.

 

[nickXedge]

… I searched a lot online and many times people would say: "hey, I got it fixed", but leave out the details…

I ran into the same problem on initial diagnosis! That's why I figured I would update this when it was resolved, even if there weren't many hits on my thread. Glad it could help you! Let me know how it goes for you.

 

[yarik]

I am very happy to update that my iMac is back online!!!
I replaced the original video card with 2600XT from Amazon, and it was, as nickXedge said, cheaper than the 2400. Double bonus)
I got the video card for 172$ and with 4 gigs of ram, it is now ready to be updated to Lion.
In future, I will probably remove the optical drive and install SSD, as well as upgrade internal HDD. I read somewhere that you can also update the processor, but that will an other project.
I hope people who find this thread will be as happy as me and nickXedge.