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568129 12-03-2011 02:52 PM

Does a 17" imac g5 logic board fit a 20" imac g5?
I have a 20" Imac g5 rev b with ambient light sensor model number M9845LL/A.
It was one of the lucky imacs to get shipped with a bad logic board due to failing capacitors. Even though the capacitors show no sign of damage on the logic board aren't swollen though. When I start it up it does not boot and I get no video and the fans are roaring loud to prevent the cpu from overheating. The third and fourth led lights don't light up on the logic board. I tried connecting an external display and the external display gets no video from the Imac g5.

The serial number of my imac is

I have a couple of questions.

Is there an apple repair extension program for this specific model of imac g5 since it is no longer under waranty?

Would a logic board from an imac g5 17" fit into my imac g5 20"?

Since I have to replace the logic board on it, how about an upgrade,would a intel logic board from an 20" imac fit into the imac g5 20"?

dtravis7 12-03-2011 03:21 PM

If the capacitors are not bulging or leaking I doubt that is the issue. There was at one time a program I believe for boards with Bad Caps.

The 17" logic board is a lot different. I am sure it will not mount in the 20" iMacs case.

The Intel board would be way different. It's more like the iMac G5 iSight in basic layout. The ALS was a way different machine inside.

Is the RAM seated properly? Did you try removing and reinserting the sticks of RAM?

It could be also a Power Supply issue. All guessing at this point though.

568129 12-03-2011 03:33 PM

thanks for your reply dtravis7.

I don't see how the logic board has bad capacitors if they are not swollen or leaking either, however some people say they go bad without any visible damage though.

I am going to check to see if the ram is inserted properly. We'll see if it is. I am going to try to remove and reinsert the sticks of ram and boot it up again and see what happens.

I doubt the powersupply has an issue because led #2 is on which means the power supply is working correctly.

Could be anything really.

dtravis7 12-03-2011 03:38 PM

I do have the Service Manuals for those machines so if I can look anything up let me know.

568129 12-03-2011 03:53 PM

thank you for the information. If I ever need to remove the logic board by myself I will let you know.

I checked the ram and was seated properly in its slot. I removed and reinstalled the ram and booted it up and still got the same problem. I even tried installing the ram in the other ram slot and still nothing.

568129 12-04-2011 07:28 PM

are you sure that the logic board from the 17 inch imac g5 is not the same as the logic board from the 20 inch imac g5 as they have the same part number 820-1747-A. Here is a link to the logic board for a 17 inch:Apple iMac 17" G5 820-1747-A Logic Board 2.0GHz Tested Working | eBay

Here is a link to the logic board from a 20 inch imac g5:imac G5 20

They have the same part number.

568129 12-06-2011 01:02 PM

imac g5 logic board
anyone know if the 17 inch imac g5 logic board fits the 20 inch imac g5?

dtravis7 12-06-2011 02:00 PM

According to the Service Manuals for both:

For the 20" ALS:
Logic Board
661-3613, 2.0 GHz,
ALS (Ambient Light Sensor)

For the 17" ALS:
Logic Board
661-3611 1.8 GHz
661-3612 2.0 GHz

So based on that I would say no. The 17" is a lot smaller machine and I think there are differences in the layout.

If you want to chance it, above is the info from apples own manuals.

pigoo3 12-06-2011 02:11 PM


Originally Posted by dtravis7 (Post 1336860)
So based on that I would say no. The 17" is a lot smaller machine and I think there are differences in the layout.

Pretty much what I was thinking (different logic board layout = doesn't fit)...but wasn't 100%.

- Nick

568129 12-06-2011 02:13 PM

thanks for the reply dtravis7

Does part number 820-1747-A correspond to 661-3613?

Dtravis7 Could you send me the service manual for the imac g5?


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