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Black Grape

macrumors newbie
Original poster
Jul 4, 2023
16
11
UK
Hi All,
I’m trying to service an iMac G4 17” and would appreciate any advice and help regarding swapping fans. The OEM fan (Superred, CHA9212DS-TF 12V DC) is very noisy. I’ve already cleaned it to a spotless finish, used new thermal paste and it’s still too noisy. I’ve read most of the posts on MacRumors about swapping the OEM fan and have some questions.

I bought the Noctua NF-A9 FLX 3-Pin (92mm) as a replacement, as it was highly recommended by other G4 users.

Questions:
1. As Noctua’s a 3-pin fan, do I simply plug the 3 pin thing from the Noctua (see below) into the Mac’s existing fan power cable?

3 Pin Close Up.jpg


2. Does the G4 have any temperature and/or processor based fan speed control?

3. If ‘yes’, where is it, and can the Noctua fan’s speed be controlled by the G4?

4. If ‘No’, I presume the Noctua fan will run at full speed ?

5. Did the OEM fan have a temperature monitor which controlled fan speed?

Thanks in advance for your insight and help!
 
Last edited:

Intell

macrumors P6
Jan 24, 2010
18,955
509
Inside
Pretty sure the G4 iMac has a dynamically controlled fan. In that the system will change the fan speed depending on how hot it gets.
 
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Black Grape

macrumors newbie
Original poster
Jul 4, 2023
16
11
UK
Pretty sure the G4 iMac has a dynamically controlled fan. In that the system will change the fan speed depending on how hot it gets.
This is what I'm hoping to find out. I've carefully read almost every thread on this topic on here and no-one can say for certain. Some people say the OEM fan had some sort of diode to measure the temperature - but how did it communicate with the CPU, if the fan only uses a 3 pin plug ? (I'm no expert on this, just a basic amateur:). Others say to just run a decent replacement fan at a level necessary to keep temperatures and noise levels at a reasonable level - which makes sense. But my big query is about the wiring..
 

Needleroozer

macrumors regular
Mar 29, 2013
137
197
This is what I'm hoping to find out. I've carefully read almost every thread on this topic on here and no-one can say for certain. Some people say the OEM fan had some sort of diode to measure the temperature - but how did it communicate with the CPU, if the fan only uses a 3 pin plug ? (I'm no expert on this, just a basic amateur:).

That sort of fan likely uses the fact that a diode’s forward voltage drop changes as a function of temperature, allowing it to use the diode as a temperature sensor and servo the fan speed to match.
That’s a totally independent form of temperature regulation; most fans provide a third tachometer output wire that allows the computer to know how fast the fan is spinning and adjust its supply voltage accordingly.
Four-wire fans have a dedicated input wire that allows the host computer to set their speed directly using a PWM signal.

Others say to just run a decent replacement fan at a level necessary to keep temperatures and noise levels at a reasonable level - which makes sense. But my big query is about the wiring..

I forgot to take pictures when I replaced the fan in my 15” iMac G4, but the connector on the fan has the opposite pin gender (male pins as opposed to female pins) as normal PC fans. So you’ll either have to use some jumper wires or just cut and splice.
The pinout on the iMac fan is:
Red: 12V
Black: GND
Yellow: Tachometer output signal

While these are the standard PC fan signals, note that this is not the standard PC fan pinout.
 

Black Grape

macrumors newbie
Original poster
Jul 4, 2023
16
11
UK
That sort of fan likely uses the fact that a diode’s forward voltage drop changes as a function of temperature, allowing it to use the diode as a temperature sensor and servo the fan speed to match.
That’s a totally independent form of temperature regulation; most fans provide a third tachometer output wire that allows the computer to know how fast the fan is spinning and adjust its supply voltage accordingly.
Four-wire fans have a dedicated input wire that allows the host computer to set their speed directly using a PWM signal.



I forgot to take pictures when I replaced the fan in my 15” iMac G4, but the connector on the fan has the opposite pin gender (male pins as opposed to female pins) as normal PC fans. So you’ll either have to use some jumper wires or just cut and splice.
The pinout on the iMac fan is:
Red: 12V
Black: GND
Yellow: Tachometer output signal

While these are the standard PC fan signals, note that this is not the standard PC fan pinout.
Thanks, @Needleroozer for that excellent overview. If you don't mind, I'll take pics of the connectors when I pry open the G4 and ask you to point out which wires need to connect to each other. I've got a wire stripper and a basic soldering iron. :) Thanks again.
 
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ThEcXMaN

macrumors newbie
Dec 5, 2022
18
10
Thanks, @Needleroozer for that excellent overview. If you don't mind, I'll take pics of the connectors when I pry open the G4 and ask you to point out which wires need to connect to each other. I've got a wire stripper and a basic soldering iron. :) Thanks again.

Hi, I'm in the same situation as you and wanted some advice.

Did you then solve the problem with the fan? I have an iMac G4 15" (very noisy), can you confirm that the Noctua you indicated will be fine? Suggestion for connection? Thank you very much, Mario
 

3922434

Cancelled
Aug 24, 2023
123
40
iMac G4 never shipped with user acessable temp sensors....They only started user acessable temp sensors with the G4 MDD and then of course on the G5 because of thermal zones and cooling down that G5 chip. They introduced one sensor in early 2004 iMac G5's and then they added second sensor both on the hard drive and optical. But there is no sensor iMac G4. The way apple designed it is with the dome acting a passive heatsink and the center fan acting to dissipate that heat....kinda like the thermal core we see in the mac pro 6,1 late 2013. So the fans run at a constant speed and it doesn't throttle down at least on the late models. I can't speak for the early ones but when we deployed them in schools I remember teachers asking why they were so much louder.
 
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3922434

Cancelled
Aug 24, 2023
123
40
dont know if this helps but I have some resource binders when we wroked on them in schools and had access to ordering parts through apples portal....The apple sku for the replacement fan is Apple part number: 922-6215, 603-3962. They were manufactured I believe by foxconn and some other company....I believe the foxconns were quieter but its been so long now I could be wrong
 
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Intell

macrumors P6
Jan 24, 2010
18,955
509
Inside
The fans in an iMac G4 do change speed. Get them hot enough, and the fans will spin up beyond their standard idle speeds. I've seen it happen on a 1.25Ghz and a 800Mhz model. While not the best tempature sensor, the hard drives included in the iMac G4 has a temperature sensor built into it and is accessible to most 3rd party temperature sensing programs.
 

3922434

Cancelled
Aug 24, 2023
123
40
Oh shoot I forgot about the SMART censor for the hard drive I didn’t think it ramped up the fans…maybe I just never noticed? Appreciate you correcting me though!!!!
 

Black Grape

macrumors newbie
Original poster
Jul 4, 2023
16
11
UK
Hi, I'm in the same situation as you and wanted some advice.

Did you then solve the problem with the fan? I have an iMac G4 15" (very noisy), can you confirm that the Noctua you indicated will be fine? Suggestion for connection? Thank you very much, Mario
Hi, yes, I can confirm that the Noctua NF-A9 FLX 3 is perfect for my iMac G4 17" model. For connecting it, just use the provided 4 to 3 pin adaptor cable supplied with the fan, to the Mac's power cable. Be sure to tidy everything away to avoid disrupting airflow. If the standard cable's too noisy, you can reduce the fan speed with one of the two additional cables supplied (NA-RC12 or NA-RC13) which reduce speed (and thus noise) by specified amounts. See photo below. I used the Noctua NF-A9 FLX 3 as it came with all necessary cables. I looked at re-wiring other fans, but didn't trust my terrible soldering skills not to screw things up! :)
Noctua Spare Cables.jpg


Here's a video of the Noctua fan installation.
 
Last edited:
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ThEcXMaN

macrumors newbie
Dec 5, 2022
18
10
Hi, yes, I can confirm that the Noctua NF-A9 FLX 3 is perfect for my iMac G4 17" model. For connecting it, just use the provided 4 to 3 pin adaptor cable supplied with the fan, to the Mac's power cable. Be sure to tidy everything away to avoid disrupting airflow. If the standard cable's too noisy, you can reduce the fan speed with one of the two additional cables supplied (NA-RC12 or NA-RC13) which reduce speed (and thus noise) by specified amounts. See photo below. I used the Noctua NF-A9 FLX 3 as it came with all necessary cables. I looked at re-wiring other fans, but didn't trust my terrible soldering skills not to screw things up! :) View attachment 2277896

Here's a video of the Noctua fan installation. View attachment 2277919

Oh wow, thank you for the precious info!

The fan will arrive Monday from Amazon and I didn't know there were so many adapters included, very good!
Can I ask you if you have connected it "standard", and is there already a good reduction in terms of noise?

As soon as the RAM arrives I will proceed with a complete change of all the components:

- internal RAM
- SSD
- new CD/DVD recorder (I had an old Pioneer DVR-107D, I hope it is compatible)
- New fan, as anticipated

Plus the usual stuff, cleaning, new thermal paste, etc

If you have any advice to give me I thank you again, you were very kind.

Thanks again, Mario
 
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Black Grape

macrumors newbie
Original poster
Jul 4, 2023
16
11
UK
Oh wow, thank you for the precious info!

The fan will arrive Monday from Amazon and I didn't know there were so many adapters included, very good!
Can I ask you if you have connected it "standard", and is there already a good reduction in terms of noise?

As soon as the RAM arrives I will proceed with a complete change of all the components:

- internal RAM
- SSD
- new CD/DVD recorder (I had an old Pioneer DVR-107D, I hope it is compatible)
- New fan, as anticipated

Plus the usual stuff, cleaning, new thermal paste, etc

If you have any advice to give me I thank you again, you were very kind.

Thanks again, Mario
Hi Mario,
Glad to help.
I also replaced the HD with an SSD, new thermal paste and pads and new fan. I was only able to do all of this because of the incredibly useful info provided on this forum. e.g. https://forums.macrumors.com/threads/imac-g4-refurbishment.2223570/

I connected the Noctua fan with the standard cable. I’m still finding it a bit noisy, despite running at 34dB. So, I may change it to the one of the slower RPM fan adaptors.

Noise levels of OEM fan.



Noise of Noctua fan. [video]


I also carefully viewed YT videos to see how the iMac came apart.

The only advice I can give is to be very, very careful and patient when taking apart the G4.

• Create some sort of pillow for it to rest on.
• Install new logic board battery.
• Resist the temptation to pull to separate components.

Create a plan of the screw positions using a piece of cardboard. This helps to keep screws in place and return screws to their original positions.

Noctua Fans spares & screw holder.jpg


When the case was opened, I created a cardboard cut out to protect the motherboard from damage. This allows the DVD to rest on a small cutting board!
Case open OEM Fan.JPG


When installing the DVD, push the connectors tight to the edge. This is difficult to explain, but you’ll understand if your new DVD doesn’t seem to fit or the DVD door doesn't open to accept a DVD.
DVD install correct screw positioning.JPG


Retain the original hard disk sticky paper cover. This can be used to cover up the SSD and cables.
Case open OEM Fan.JPG


Based on info from this forum, I added extra thermal pad to the base.
Thermal Pad on base.JPG


Removing the logic board to clean underneath is a real bitch.
Check the DVD drive tray opens before and after you re-attach the two parts of the iMac.
I used a Startech IDE connector - based on forum recommendations.
I used 99% Isopropyl alcohol to clean the motherboard, wipe away old thermal paste etc. DO NOT use this on the iMac exterior housing!

I’ve got more videos but can’t upload them here (keep getting error message), even when the file size is <100Mb.
So, here’s a link to a folder with these videos. It’s available for ONE week only.
https://www.filemail.com/d/emawfkltyjjecby

Hope this helps and have a beer ready to take a relaxing drink when things aren't going well! :)
 
Last edited:

ThEcXMaN

macrumors newbie
Dec 5, 2022
18
10
Hi Mario,
Glad to help.
I also replaced the HD with an SSD, new thermal paste and pads and new fan. I was only able to do all of this because of the incredibly useful info provided on this forum. e.g. https://forums.macrumors.com/threads/imac-g4-refurbishment.2223570/

I connected the Noctua fan with the standard cable. I’m still finding it a bit noisy, despite running at 34dB. So, I may change it to the one of the slower RPM fan adaptors.

Noise levels of OEM fan.

View attachment 2278655

Noise of Noctua fan. [video]
View attachment 2278668

I also carefully viewed YT videos to see how the iMac came apart.

The only advice I can give is to be very, very careful and patient when taking apart the G4.

• Create some sort of pillow for it to rest on.
• Install new logic board battery.
• Resist the temptation to pull to separate components.

Create a plan of the screw positions using a piece of cardboard. This helps to keep screws in place and return screws to their original positions.

View attachment 2278670

When the case was opened, I created a cardboard cut out to protect the motherboard from damage. This allows the DVD to rest on a small cutting board!
View attachment 2278671

When installing the DVD, push the connectors tight to the edge. This is difficult to explain, but you’ll understand if your new DVD doesn’t seem to fit or the DVD door doesn't open to accept a DVD.
View attachment 2278676

Retain the original hard disk sticky paper cover. This can be used to cover up the SSD and cables.
View attachment 2278677

Based on info from this forum, I added extra thermal pad to the base.
View attachment 2278678

Removing the logic board to clean underneath is a real bitch.
Check the DVD drive tray opens before and after you re-attach the two parts of the iMac.
I used a Startech IDE connector - based on forum recommendations.
I used 99% Isopropyl alcohol to clean the motherboard, wipe away old thermal paste etc. DO NOT use this on the iMac exterior housing!

I’ve got more videos but can’t upload them here (keep getting error message), even when the file size is <100Mb.
So, here’s a link to a folder with these videos. It’s available for ONE week only.
https://www.filemail.com/d/emawfkltyjjecby

Hope this helps and have a beer ready to take a relaxing drink when things aren't going well! :)

Hi,

In the meantime, a big thank you for the invaluable information. I always have little time to respond, and I apologize for this, some information has been lost.

- meanwhile I apologize for the crossposting, I needed specific information on the fan, but I had written a specific thread: iMac G4 lamp base model: worth it?

- the iMac G4 in my possession is unfortunately the first version, 800Mhz, Usb1: I also found useful information in the thread you indicated previously for correct disassembly/upgrade.

- unfortunately I had to use 99% ispropyl alcohol to remove those stains / glue you see in my thread, I cross my fingers and hope I haven't done any damage. Only in this way was it possible to remove those stains.

- I confirm that I have downloaded all the videos you kindly shared.

These are the updates: all the parts have arrived except the OWC ram. As soon as it arrives I will proceed with the disassembly. Thanks again and I will study the videos carefully (congratulations for the work you did!) 👍
 

Black Grape

macrumors newbie
Original poster
Jul 4, 2023
16
11
UK
Hi,

In the meantime, a big thank you for the invaluable information. I always have little time to respond, and I apologize for this, some information has been lost.

- meanwhile I apologize for the crossposting, I needed specific information on the fan, but I had written a specific thread: iMac G4 lamp base model: worth it?

- the iMac G4 in my possession is unfortunately the first version, 800Mhz, Usb1: I also found useful information in the thread you indicated previously for correct disassembly/upgrade.

- unfortunately I had to use 99% ispropyl alcohol to remove those stains / glue you see in my thread, I cross my fingers and hope I haven't done any damage. Only in this way was it possible to remove those stains.

- I confirm that I have downloaded all the videos you kindly shared.

These are the updates: all the parts have arrived except the OWC ram. As soon as it arrives I will proceed with the disassembly. Thanks again and I will study the videos carefully (congratulations for the work you did!) 👍
Glad you found the vids useful. To clean the G4 exterior I used Mr Muscle with a soft cloth! Try a small, inconspicuous area first. Let me know if you need more info. I learnt everything about repairing the iMac G4 by searching through this forum, so it's great to be able to give something back!
 
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CooperBox

macrumors 68000
Hi Mario,
Glad to help.
I also replaced the HD with an SSD, new thermal paste and pads and new fan. I was only able to do all of this because of the incredibly useful info provided on this forum. e.g. https://forums.macrumors.com/threads/imac-g4-refurbishment.2223570/

I connected the Noctua fan with the standard cable. I’m still finding it a bit noisy, despite running at 34dB. So, I may change it to the one of the slower RPM fan adaptors.

Noise levels of OEM fan.

View attachment 2278655

Noise of Noctua fan. [video]
View attachment 2278668

I also carefully viewed YT videos to see how the iMac came apart.

The only advice I can give is to be very, very careful and patient when taking apart the G4.

• Create some sort of pillow for it to rest on.
• Install new logic board battery.
• Resist the temptation to pull to separate components.

Create a plan of the screw positions using a piece of cardboard. This helps to keep screws in place and return screws to their original positions.

View attachment 2278670

When the case was opened, I created a cardboard cut out to protect the motherboard from damage. This allows the DVD to rest on a small cutting board!
View attachment 2278671

When installing the DVD, push the connectors tight to the edge. This is difficult to explain, but you’ll understand if your new DVD doesn’t seem to fit or the DVD door doesn't open to accept a DVD.
View attachment 2278676

Retain the original hard disk sticky paper cover. This can be used to cover up the SSD and cables.
View attachment 2278677

Based on info from this forum, I added extra thermal pad to the base.
View attachment 2278678

Removing the logic board to clean underneath is a real bitch.
Check the DVD drive tray opens before and after you re-attach the two parts of the iMac.
I used a Startech IDE connector - based on forum recommendations.
I used 99% Isopropyl alcohol to clean the motherboard, wipe away old thermal paste etc. DO NOT use this on the iMac exterior housing!

I’ve got more videos but can’t upload them here (keep getting error message), even when the file size is <100Mb.
So, here’s a link to a folder with these videos. It’s available for ONE week only.
https://www.filemail.com/d/emawfkltyjjecby

Hope this helps and have a beer ready to take a relaxing drink when things aren't going well! :)
What an excellent write-up! And thanks for linking to my help video. Pleased it served it's purpose.
 
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CooperBox

macrumors 68000
Standing on the shoulders of giants! Thanks for your stuff,
It wasn't too long ago that I didn't know what a RAM memory module was and thought that climbing Everest would be more feasable than me opening up any computer. And if anyone had asked about thermal paste, I'd have guessed that it may have been something to brush on and to warm up teeth.....!
 
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