Addressing the 24″ iMac.

While the logic board from a 20″ late-2006 iMac is out for repair (update here, I received the Nvidia 7600 graphics card – purportedly new – from ApplePalace.com – $263 with tax and shipping to my CA address. This is for my late-2006 24″ iMac. The graphics in both machines are shot. The vendor had assured me when I called that the part was new and came with a 60 day warranty; the invoice states 30 days. Either way, that’s enough to install and test it.

So, using the Apple Manual for this model, found here, I dismantled the computer and took a look around. First, the machine is quite a bit easier to take apart than the 20″ model. No secret catches for the bezel, no black tape everywhere and no need to remove the optical drive to extract the mother board.

Whereas the GPU in the 20″ and 17″ models is soldered to the logic board, in the 24″ model it’s plugged in and retained with three screws. Apple offered the machine with a 2.16gHz C2D/Nvidia 7300 combination or with a 2.33gHz C2D/Nvidia 7600 pairing. I bought the latter card as the replacement, as it has twice the video ram at 256mB, so I will end up with a 2.16gHz/Nvidia 7600 iMac. GPU speed/memory is far more important for graphics intensive activities like photo processing, so this seems to make sense. With CA tax, the premium for the 7600 model is $50, both new.

As with the 20″ iMac, simply replacing the part makes no sense. The problem – inadequate cooling – will not go away and you will likely be doing the same thing all over again and, like a bad mechanic, simply throwing money at the problem. Better cooling is required.

As my 24″ iMac is worked very hard for both business and pleasure, I decided to go the whole hog and drill cooling holes for the GPU radiator, the power supply and the hard disk drive. (I only addressed the first two on the 20″ model as it has a far easier life and the HDD is the least troubling of the three when it comes to heat issues.) Those are the three greatest heat generators, in that order. As there’s much more space in the 24″ iMac’s body, the design of the GPU cooling splits the cooling between the GPU and the GPU Diodes with separate radiators, mounted above one another. As in the 20″, a fan blows air across the fins to confer cooling and copper pipes are again used to conduct heat from the GPU and diodes. The snag is that the hot air emanating from the GPU and diodes blows directly on the power supply above! (In the 20″ the power supply is off to the side.) No wonder the latter gets hot – it has no cooling fan of its own.

When I purchased the iMac (used – documented in this blog in detail) I immediately installed a 1 terabyte Samsung hard disk drive. The HDD is cooled by its own fan but also runs hot, so I decided to provide cooling holes for the HDD also. I have no comparative data as to whether a 1 tB drive runs warmer than the 250 gB Western Digital junk Apple installed in these models, but the additional labor to cool the HDD is, in any case, minor.

The layout of the components in the 24″ model differs from that in the 20″ model, so the following self-explanatory pictures will help you to determine where to drill holes. As before, the grid is 3/4″ and the holes 3/8″.

The whole logic board still has to be removed to get at the exchangeable GPU, which is screwed to the back (three screws) and very firmly clipped in to the connector on the logic board. There’s no way you can get replacement wrong as the two screws on the circuit end of the assembly will not fit if a proper connection has not been made between the GPU and logic board. Mine needed a firm push and engaged with a ‘click’,

Overall layout

Hard Disk Drive

Power Supply

GPU and GPU Diode radiators – the plate on the left is for wall mounting

Grid for the Power Supply

Grid for the HDD

Grids for the GPU and GPU diodes

Inside view showing silver paper cut away

Old GPU on logic board, new above

Rear of GPUs – new on left distinguished by ‘256’ label

The rest of the procedure is much as for the 20″ model described in Part II. That is, once drilled, the holes are de-burred and high temperature Loctite adhesive is used to retain aluminum mesh on the inside to act as a dust shield.

I wore out two more Forstner bits doing this in addition to the one worn out on the 20″ iMac. Seems they are good for 40-45 holes each before giving up the ghost.

If you want to install a larger HDD in your iMac, now would be a good time.

My one fear is that the diodes for the GPU, are also fried. Those are soldered to the logic board so if the problem does not go away (slow downs, beachballs, etc.) then the mother board itself will have to be sent in for repair. Even so, I will end up with a machine with, hopefully, significantly enhanced graphics performance – and proper cooling.

A few words on thermal paste:

There is no magic to thermal (or heat) paste. Its purpose is to enhance contact between two surfaces – one a heat generator, the other a heat sink. It simply fills the microscopic imperfections in the surfaces with its conductive medium and, when the two are squeezed together, optimizes transfer of heat from generator to sink.

The 20″ and 24″ iMacs use two radiators – one for the GPU, the other for the GPU diodes. Both terminate in copper plates (heat sinks) which are in intimate contact with the GPU and GPU Diode, respectively. And between each is a thin layer of thermal paste.

In the 20″ both surfaces must be cleaned and new thermal paste applied. In the 24″, if you are just changing the Nvidia GPU, the replacement GPU comes with thermal paste installed and need only be plugged in and screwed down. However, there’s no harm in renewing the thermal paste for the GPU diode whose radiator/heat sink is fastened to the mother board with four T8 screws through the heat sink (a copper plate) and one through the side of the radiator. Remove these five screws and follow the next three pictures, after disconnecting the small cable attached to the heat sink circuitry.

Old thermal paste – note the squeeze out. Note the detached cable also.

Surfaces cleaned with Isopropyl alcohol and a Q tip

New thermal paste applied – I removed some as this is a bit too much!

Don’t forget to reconnect the cable or your graphics will be well and truly dead!

‘Experts’ will regale you with the right amount to put on but that’s all nonsense. Just make sure you have enough to cover both contact surfaces so that the base material does not show through (OK, a little less than I used above!) and then tighten down the heat sink. The design is optimized to ensure just the right amount of pressure between diode and heat sink using those nicely engineered sprung posts, and any excess will simply squeeze out. How do you think the squeeze out in the first of the above three pictures happened in the first place? Just don’t mess with the adjustment of the sprung posts.

Once I have everything together I will post a piece on performance for both the 20″ and 24″ machines.

More drilling.

Here are the measurements you need to drill your 20″ iMac case for better ventilation. Use the ‘iMac’ logo as an additional guide. I will provide data for the 24″ iMac in a subsequent piece.

Drilling specs for iMac 20″ – 2006 models

These are for use with a 3/8″ Forstner drill bit, as explained yesterday. The second set of holes to the right is to enhance cooling of the power supply, the other major heat generator in the tight confines of the iMac enclosure. The grid spacing is 3/4″ – use a Sharpie ultra fine market then remove the markings with Isopropyl alcohol when finished.

Here’s how the power supply holes look from the inside – the aluminum sheet has been cut away:

Power supply cooling

Here’s a like picture for the GPU cooling unit:

iMac GPU cooling holes

Before gluing in wire mesh to restore conductivity to the static shield and to help reduce dust intake, the holes are de-burred on both sides with a conical abrasive bit:

De-burring the holes

I use Loctite Repair Extreme for gluing the mesh in place, as it is rated for high temperatures and adheres well to the aluminum mesh and the iMac’s plastic casing. The specs on the package state that the glue will function in a temperature range of -58F to 248F (5C to 40C); their web site states -50F to 400F. Either is more than adequate. If your GPU or related capacitors get up to 200F you have bigger things to worry about than melting glue! The Loctite product code is 01-06821-02.

This adhesive has a five minute work time before it starts to set, which means there’s no need to rush to get the mesh positioned just so. Just make sure it’s flat before you install it, then you can simply tamp it down on the adhesive beads with a stick or whatever. It takes 24 hours to fully cure.

Glue lines

Here’s the mesh in place for the GPU cooler. The power supply mesh has already been installed and the power supply – lower right – has been refastened to the case:

GPU wire mesh

And here’s the final view from the rear after removing the Sharpie marks using Isopropyl alcohol. The mesh is visible through the holes. As you can see, with a bit of planning and care the result can look reasonably professional:

The final result

I wore out two more new Forstner bits doing this. Seems they pretty much give up the ghost after 40-45 holes have been drilled.

Now I have to wait for the logic board to come back from the repair shop.

I will start work on the 24″ iMac once the Nvidia 7600 GPU arrives – it’s in the mail right now. The Forstner bit is completely shot so I have blown another $8 on a new one for the 24″ iMac. The last thing you want to do is force a blunt drill bit though the iMac’s plastic casing, robust as it is. You only get one chance to do this.

For those proposing to do this surgery on their late-2006/early-2007 24″ iMac, you can download Apple’s Technical Service Manual here. It makes a seemingly complex task easy.

Manuals for many other more recent models are listed here.

In Part III I will address the correct application of fresh thermal paste between the heat sinks and the ATI GPU and related diodes, respectively. This is a key step before reassembly, which is currently awaiting the return of the repaired logic board.

Fixing cooling issues.

This piece is relevant to users of the 17″, 20″ and 24″ white iMacs with Core Duo (early 2006) or Core2Duo (late 2006) CPUs. These machines use the Intel GMA950, ATI 1600 and Nvidia 7300 (or 7600 on top end 24″ machines) Graphics Processing Units (GPUs), respectively.

When I bought my 24″ iMac I wrote here of my concerns of the poor cooling of critical components, occasioned by Apple’s obsession with looks at the expense of sound engineering design.

Many are doomed to fail owing to improper venting of hot air generated by the GPU. Indeed, if you look on Apple’s own discussion board at this thread, now some 28 pages long and counting, you will see the raft of complaints about blown GPUs on all models, regardless of GPU maker. Apple has yet to admit – if it ever will – fault, and life is simply too short to argue with them, so I decided to fix things myself. Plus they have $30bn in the bank and lots of mean lawyers ….

Things have come to an unhappy pass. Both my 20″ iMac (ATI 1600) and my 24″ iMac (Nvidia 7300) are showing advanced symptoms of GPU failure, despite the judicious use of Fan Control to speed up the GPU fan. Symptoms include horizontal and vertical lines on the screen, distorted areas and random rectangular colored patches. Add slower operation and many spinning beach balls and the machines are becoming simply unusable.

A PRAM reset, what you’ll likely be told to do by Apple, makes no difference.

Here’s the diagnostic language from Apple’s own repair manual:

Obviously they want it unplugged for two hours. It has to cool down, get it?

And while you are at it, cease being naïve – Apple is just another big corporation looking to maximize profits, bless them – the customer most certainly does not come first as this language in the same manual relating to dead LCD pixels clearly discloses:

“Don’t tell the customer”

So you are going to have to look after yourself, make some money on AAPL stock or elsewhere and get with the action. The guts of a modern Intel Mac are made by the same manufacturers used by PC makers – Intel, ATI, Nvidia, Samsung and LG Philips LCDs, WD/Seagate HDDs, etc., etc. They just come in a prettier (and costlier) box which, in this case, is poorly designed. Use the machines for the superb OS, but don’t expect too much costly integrity from the manufacturer. Read on.

Now Apple will charge you $900 to replace the logic board on the 17″ and 20″ models, whereon the GPU is well and truly soldered. Maybe less on the 24″ model where the GPU is a separate plug in module – I have read $400 or so. Either way, it’s highway robbery. And while iMacs start at $1200 new, there’s no alternative for users like us – and surely all photographers out there – who despise glossy screens. And, finally, there’s a simple sense of outrage at throwing away an otherwise fine machine after just 2 years of light use.

So we decided to repair things and not at Apple prices. My 20″ iMac’s logic board was shipped to Apples-R-Us for a $195 repair of the fried diodes and capacitors. For my 24″ model I had the choice of replacing the Nvidia 128mb GPU with a like model at $179 or upgrading to the faster 7600 model at $231 with 256mb, so I opted for the latter. This is a new part, not a fried recycler special (I asked) with a 60 day warranty.

Now surgery, the title of this piece, is meant to excise the bad and restore the patient to health. Simply replacing fried parts with new or repaired ones which would be fried again is pointless. So some thinking was called for to see how better to confer proper cooling on the GPU and its diodes.

First, extracting a motherboard (or logic board, as Apple calls it) from an iMac is …. a mother. Do yourself a favor and download the official late-2006 Apple repair manual by clicking below.

The tools needed are very few – Torx #6, 8 and 10 screwdrivers, a Philips #2, a magnetizer for the screwdrivers, a lollipop stick to remove the black sheeting around the LCD (20″ model only), lots of plastic baggies for all the fasteners you will be removing, a cool head and a pair of balls. The instructions in the Apple manual err in only two particulars. They forget to mention that the RH speaker has to be removed to remove the logic board and that the cooling radiator for the GPU has to be removed once the logic board is extricated, before shipping the latter for repair. Eight T8 screws – no biggie.

Let’s take a look at how Apple cools the GPU and related diodes. The design could hardly be more elegant.

The iMac radiator assembly in the 20″ model

It’s like a car really, absent the coolant pump. The coolant circulates by convection through the copper pipes, discharges its heat to the fin assembly (silver in the picture) whence it’s blown out by the large (black) fan. Snag is, El Jobso loves smooth, slim boxes, so the heat can only escape through a narrow slot at the top rear of the iMac. Given that heat rises, the width of the slot is useless. Basically, the GPU radiator is trying to discharge enormous amounts of heat through a 5″ x 1/4″ slot. Things are not helped by the fact that the power supply, immediately to the left, is trying to do much the same through its few inches of slot. It’s like non-taxpayers lining up for the latest bailout. Not enough taxpayers are available to feed the greedy unemployed masses. Not enough outlets for all that hot air in the iMac.

Simply stated, more outlets are needed to allow hot air to escape. Like so:

Holes being drilled in rear case of iMac behind radiator assembly

To do this, use a Sharpie marker and a Forstner 3/8″ drill bit after you have gutted your iMac. The grid is 3/4″. The Forstner bit cuts holes from the outside in, unlike a regular drill which cuts from the inside out and is guaranteed to cock-up (technical term) your placement as it skids all over the place. And you do want it to look half decent, even if the rear of your iMac faces a wall. The sharp central tip of the Forstner bit makes that child’s play.

The placement of the grid of holes is offset from center as is the position of the radiator. Use the above picture as a guide – I will post pictures for the 24″ model later. Be careful – you do not want to drill into the metal chassis underneath and you will if you get this wrong. You can get a Forstner at better hardware stores.

3/8″ Forstner bit in hand drill

When all is said and done, I will have 30 3/8″ diameter holes which will increase the area through which hot air can escape by 268%. Any burrs can be easily removed with a conical abrasive bit, and the Sharpie marks wiped off with isopropyl alcohol. So I’m optimistic that this is surgery, not placebo.

Oh!, by the way, you say you like glossy screens and your new iMac in aluminum and black is just fine? Well, be prepared. Reports of like failures of the GPUs in those are beginning to come in – and they have even less space for cooling inside. There’s that obsession with thinness again. Great for Vogue models. Not so good for electronics.

In Part II I provide detailed measurements for drilling the ventilation holes in a 20″ iMac, together with illustrations of how to install conductive aluminum mesh to both reestablish the electrostatic barrier provided by the aluminum liner in the case (which must be selectively cut away for the holes to work) and to filter out dust from the innards. The 24″ iMac will be addressed later – I can only deal with one Apple screw-up at a time.