09-10-2010, 04:43 PM

Hey all,

So, I replaced the hard drive in my friends 20" iMac today. This is a procedure I've done before with very few issues, if any at all.

That is, until today!

I put it back together and I boot it up with the Snow Leo DVD inserted.

It makes the normal start-up chime, and the light comes on (and stays on), but the display does not turn on.

It sounds like the computer is working normally. In fact, if I hold down C to boot from the DVD, it sounds like it's going into the installation process.

I notice that the time it takes to shut down the computer using the power button goes from instant to requiring it to be held down for a few seconds, as if it's in a program and the power button is not allowed to be the instant-off.

Is the display shot? I am hard pressed to believe it's the logic board because, like I said, it sounds like it is going through the regular processes of booting from the DVD and getting ready to install the OS.

Thanks in advance.

Edited to add: I have tried resetting the NVRAM and PRAM and SMC. Bupkis still. The power light is staying solid, which I neglected to mention. Kind of leads me to believe it might be the logic board? I really don't understand how I could have fried it though. I'm very safe with my ESD practices and work area...

09-10-2010, 10:57 PM

Replacing a hard drive in an iMac requires removing the entire display panel before access into the machine. Off hand, I would say go back over your work and make sure you got everything back together OK and all cables attached, etc. I can't tell you how many times I've done a certain electronic repair only to find out that time 99 I screwed up and forgot something. The other 98 times were a piece of cake. I think you get the drift...

09-11-2010, 12:33 AM

Thanks for the reply.

I quadruple checked everything I did, but I come up short.

The only thing I can think of is that the temp sensor connector that plugs into the logicboard was super fragile and just fell apart when I tried to unplug it. I reconnected the wires in the exact order that they came out in, but still nothing.

It might be worth it to just order the $39 wire to see if that is actually it, but I really doubt it.

Thoughts?

09-11-2010, 01:33 AM

Yeah, that's a tough one. If you've gone over your work several times and everything looks OK, it's hard to say what could have happened. The thermal sensor, even if it was disconnected would not cause the screen to be off.

Let's think for a minute.... what is needed for the display to light? We need an inverter to provide power to the backlight, we need a good backlight to light the screen and all associated power cables. Of course the display also has to be OK. I might be overlooking something. Bad logic board? I don't think so but I guess anything is possible.

Have you tried hooking an external monitor up to see if you can get it to work? Or maybe hooking another Mac in Firewire Target mode?

09-11-2010, 02:00 AM

*sigh* it is a hard one, eh?

I'll try an external display to see what happens. A 20" iMac has an external display output though? The iMac is back with her owner so I can't check right away.

Your thought process is totally correct though. Inverter, backlight, and display. However, I don't have any of those spares so I can't really start swapping the components out until I find the bad one.

I think I'll try to format and install the OS using target disc or an external display and see what happens.

Otherwise, it might be off to Microcenter for a $70 diagnostic. I'll bet they just say it's the logic board though. =/

Thanks for the brain storming!