This is a fairly technical problem and I won't bore you with the details here, I just wanted to document how prevalent these defective chips are as I am regularly required to repair failed GPUs on a regular basis. In fact just today we booked in this Mac which in all honesty has been very well looked after and lucky to have survived for this length of time.
model: A1200 You have to look closely to see the faint horizontal lines
Usually to repair this fault we need to re-flow the graphics chip, but before we completely remove the main-board and send to it to our offsite facility we will try to reapply the thermal compound and re-seat the heat-sink and remove and obstruction to the cooling fans or cooling system. The main indication that this may be a more straightforward repair is the green apple logo displayed on boot.
When booting the iMac freezes on a green Apple Logo
We start by removing the plastic frame which is held in place using a combination of adhesive tape and metal clips. There a certain way to remove this and any excessive force applied can break the plastic and you will need to buy another frame. You will also need to remove the memory cover and use a torx screw driver set to remove the two screws holding the cover in place.
Its also a good idea to remove the memory at this stage
Running your fingers around the edges and applying heat from a hot air gun melt the adhesive and gradually start to pry away the frame, start from the bottom first as there are two flex cables at the top attached the front facing camera that can easily become severed if too much force is applied.
Removal should be fairly smooth if carefully extract the frame
We can now remove the 8 screws that hold the screen in place, be careful not to pull the screen too far forward as you can easily severe the screen cable, this repair was never for the faint of heart but I hope that illustrating the whole process will encourage some engineers to take on this repair themselves instead of outsourcing it.
you can easily remove the cables by tilting the screen forward
We can now start removing all the screens and cables that are holding the main board in place, its important to note where each one came from so you can ensure the screws are put back where they come from, each screw is a different size and serves a different purpose, but as we mentioned earlier this repair is for an experiences technician only so I don't think any of you will struggle with that.
The graphics card is fortunately discreet so it can be removed ( reverse side)
The main board requires gentle tugging and pulling to dislodge from the chassis but can be removed with minimal of effort provided all screws and flex ribbons have already been removed. There is no need to adjust or remove the hard drive, but you will need to remove the speaker in order to get the board out.
The graphics chip is on the flip side of the main board, it is held in place by four TORX screws and a large heat sink and fan assembly, pictured below
You may as well replace the thermal paste for the CPU while you're in.
Now comes the difficult part, this is an extremely delicate component so be very careful that you don't apply too high a temperature, I used a 400 degree heat gun to slowly bring the GPU up to temperature. I also used arctic silver as a replacement compound to the default Apple one.
Fortunately the GPU is a discreet component and could be replaced
Our aim however in this case is to repair the existing gpu to keep the cost down for the customer, we quoted £180 for this repair the customer wanted the iMac returned to him quickly so we charged a premium in this case, we can mask off the surrounding chips with foil to isolate the main chip, then gently preheat it.
the iMac chassis void of most of its internal components
after reassembling the main board and reinserting the graphics chip we are ready to test the machine to
see if it lives. The video below was shot immediately after re installing the board and powering on the machine, fingers crossed.
First boot after repair of Nvidia chip
Success! it lives, fully booted into MAC OS and running much cooler than before, as indicated by the fan exhaust blowing cool air after continuous use.
Running your fingers around the edges and applying heat from a hot air gun melt the adhesive and gradually start to pry away the frame, start from the bottom first as there are two flex cables at the top attached the front facing camera that can easily become severed if too much force is applied.
We can now remove the 8 screws that hold the screen in place, be careful not to pull the screen too far forward as you can easily severe the screen cable, this repair was never for the faint of heart but I hope that illustrating the whole process will encourage some engineers to take on this repair themselves instead of outsourcing it.
We can now start removing all the screens and cables that are holding the main board in place, its important to note where each one came from so you can ensure the screws are put back where they come from, each screw is a different size and serves a different purpose, but as we mentioned earlier this repair is for an experiences technician only so I don't think any of you will struggle with that.
The main board requires gentle tugging and pulling to dislodge from the chassis but can be removed with minimal of effort provided all screws and flex ribbons have already been removed. There is no need to adjust or remove the hard drive, but you will need to remove the speaker in order to get the board out.
The graphics chip is on the flip side of the main board, it is held in place by four TORX screws and a large heat sink and fan assembly, pictured below
Now comes the difficult part, this is an extremely delicate component so be very careful that you don't apply too high a temperature, I used a 400 degree heat gun to slowly bring the GPU up to temperature. I also used arctic silver as a replacement compound to the default Apple one.
Our aim however in this case is to repair the existing gpu to keep the cost down for the customer, we quoted £180 for this repair the customer wanted the iMac returned to him quickly so we charged a premium in this case, we can mask off the surrounding chips with foil to isolate the main chip, then gently preheat it.
after reassembling the main board and reinserting the graphics chip we are ready to test the machine to
see if it lives. The video below was shot immediately after re installing the board and powering on the machine, fingers crossed.
Success! it lives, fully booted into MAC OS and running much cooler than before, as indicated by the fan exhaust blowing cool air after continuous use.
