iMac HW Tips

Many guideline exist on internet like ifixit + youtube. Will outline a few tips having done a few of these

Drain Power Supply Before Working

• Press power button after power is disconnected for 15-20s a couple of times.

• Best to wait a day before opening (ultra safety precaution)

• Avoid touching PSU board when disconnecting the connector to the PSU

Lay iMac on its Back

Lay iMac on its back with a rolled towel to minimize the weight pressure on the stand hinge. I have fixed 27" iMacs before where the screen fell over when removing vertically and ripped out the LCD connector.

Avoid Scratching LCD

When protective glass is removed. the soft LCD glass is exposed. Droppig a screw or tool on it cause a scratch (visible with LCD is on) instantly. Hold your finger over Torx driver when removing the LCD screws to avoid drops.

Those strong magnetics nearby makes working this more difficult as well but luckily they just suck the screw right to them. Use a angled tip tweezer helps

Read first 1-2 steps of this Thunderbolt Display Guide, similar precautions

https://www.ifixit.com/Guide/Apple+Thunderbolt+Display+Black+Blanking+Out+Repair/175666

Pull Up LCD

2 people is helpful but I've always done it with myself with more experience. Head worn light helpful AND a small flash light (metal bodied one might want to rest on a insulating towel haha) helpful to peek under darkness when tilting LCD and disconnecting cables.

• With LCD laying on its back, a L tip pick can help to pull up on one corner of the heavy LCD assembly (27" one!) so you fingers can catch the rest.

• Can tilt up only ~10 degrees (2009 27" very short cable!) before having to remove vsync cable (left upper corner looking from front) Then maybe ~25-30 degrees to squeeze the side clips to remove LCD connector.

• Can tilt ~45 degrees to disconnect LCD temp sensor and PSU connector.

Reverse cable sequence for install.

vSync Connector

11,1 has just a ribbon cable with a glued on stiffener. Most of the stiffener will fall off and when inserting it back without it, will fold up the 4x traces and make a mess. Best to reglue back the stiffer. Take care and clean the surfaces with ISO and super glue back the stiffener as its necessary for vsync to make good connection. If repeatedly connect without stuffener, the vsync traces on the cable will lift off and will fold/twist/bend when you connect it.

Clearance and Lighting dis/reconnecting LCD

During removal and reinstall, dis/reconnecting the 4 cables on LCD can be a bit tricky. Here are some good tricks for temporary stand and lighting

Read first 1-2 steps of this Thunderbolt Display Guide, similar precautions

https://www.ifixit.com/Guide/Apple+Thunderbolt+Display+Black+Blanking+Out+Repair/175666

Here is how to use a small rubberized flashlight and small box to reconnect the heavy 27" LCD. I see a lot of people jamming and breaking this poor little connector without good lighting and technique.

LCD Connector Dis/Reconnect

• 2009-2010  have wider connector with squeeze tabs on both ends

• 2011 have smaller more fragile connector with a flip up/down latch that must be dis/reenaged during removal/install. These smaller connectors are also really easy to damage if trying to blindly push insert back in. Best to have proper lighting and any eye sight correction eye wear as necessary

Blow Out the Dust Bunnies

Compressed Air blows out the dust bunnies with easy. But there are several precautions. If uncomfortable, best avoid causing damage.

• Don't set huge air pressure which can cause more damage. 50 PSI is good enough. Lower air pressure goes slower but less chance for damage.

• Obviously don't just blow everywhere and not be careful. Speakers are more fragile, lots of fragile cables etc.

• Don't blow ont the fan with it spinning. It could damage the bearing. hold the fan still with a finger (and a thin screw driver for the center fan from the rear)

• Try to blow out the dusk bunnies from under the power supply and the heat sinks.

• Blow out the dust bunnies from inside out the bottom where the ram are installed. All the air inlet holes are down there.

SSD Replacements

https://sites.google.com/view/macs-stayin-alive/hw-tips#h.r0w9a1i7bdc1

GPU Sink Temp Connector

For 11,x Located under and inward main PCB assembly. I use an angled tweeser to assist. Becareful with sharp pick tip as connector has 2 thin wires. Male end of connector also angled so not easy to pull down and not slip with a sharp tweeser tip. Maybe needlenose plier might work better.

For 12,x GPU and heat sink temp connector can not be removed without removing entire logic board.

GPU X-Bracket Issues

Reusing original X-Bracket is best but requires heat to remove it (stick on) Replacement GPU card has X-Bracket with smaller bolt holes. Some vendor press these smaller holes out. However, if the holes are not beveled after pressing out, bolt head will stand taller and risk touching logical board causing random shorts. Here is a summary

https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-32931003

Display Cable Connector

11,x

This connector is easy to damage. Not much clearance when removing and inserting the GPU card + heat sink. 

Have actually repaired a connector that ripped off from someone doing SSD upgrade while removing screen with iMac standing vertically. That requires more soldering equipment and skill haha.

12,x

GPU card and bracket can only be removed with full logic board removed. Much more room and won't damage the connector (smaller than 11,x)

27" Logic Board Removal Care

Avoid knocking off L5500 Inductor

On 12,2, CPU fan and Ambient temp connector requires quite a bit of force to remove and easily knocks off the L5500 inductor which will trigger full CPU and ODD fan speed. See here

https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-33656516

21.5 Logic Board Reinstall Care

Avoid ripping cables

A few cables runs near one of the logic board's screw post near the right side fan. Very easy for the cables to get crimped under the post. Look carefully in this area prior to fully seating the logic board and reattach screws. Here is a pic where I've poked through the insulation for a couple of wires without guiding the cables from under the post.

Avoid knocking off components

Under USB sports is a rubber strip protecting some small components. Board slots into a plastic clip inside the chassis. Very easy to pinch the coner and knock off a component. A tiny component was knocked off its solder pads during my assembly and lost a USB port. Was able to resolder but very difficult (0402 - 0.4mm x 0.2mm size component) Also taped the rubber pads in the region to secure it so doesn't slide off when slotting into its clip

Avoid knocking off wire clip

This wire clip near left side fan is easy to knock off during logic board insertion. Then it blocks the board from seating fully. Make sure logic board clear this clip during reintall

Reinstall iMac

Only necessary to put in top 2 corner screws for testing. Leave the rest out in case need to open again

LCD Backlight Blanking Often

This is not a +metal GPU issue but a common issue for Apple's non glued on 27" (<= 2011 iMac 27" and Thunderbolt Displays). The 27" LCD made by LG. The backlight connector has a weak solder joint that weakens over time and thermal cycling and needs reflow. Unfortunatly need to take apart the whole display which is both delicate and potentially introduce dust/hair behind the LCD and will show up on screen. But no choice if this is happening. I've fixed about 10-15 of these now.

macrumors post #1 Spoiler 8 -> Spoiler Q18 has a couple of links. One is mine with a full PDF document on tear down and repair. The other one is someone's video.

Subtle Brightness Flickering

If have subtle  brightness flicker but doesn't go all the way to black,  its likely the backlight inverter board. Fixed 2 iMacs (one 21.5", one 27") with a used inverter board from ebay. Checked all the capacitors on both failing boards and they are fine so failing component is elsewhere. Inverter boards are cheap ($4 for 21.5 and $10-$15 for 27") so didn't pursue diagnosing the board future (not easy to diagnose anyways as boards are buried and difficult to probe with LCD mounted)

GPU Install

GPU card can come very close to the logic board. X-Bracket screws can touch the logic board if X-Bracket is changed and have less bevel to sink the bolt head. It is best to protect these potential contact regions with insulation tape. Check clearance carefully