iMac Temperature Sensor Dummy Load

iMac Temperature Sensor Dummy Load

This is an update to my other posting about the upgrade of my 2010 iMac to the Samsung 840 SSD. In that post I had an issue with controlling the HDD fan since the sensor was unable to be connected to the SSD. With the sensor disconnected the fan would run at full RPM continuously. I was able to control the speed with software on just about every event the computer would go through, such as startup, shutdown and wake from sleep. The only event I couldn’t control was wake for network access. That event occurs when I access the iTunes library from the Apple TV at which point the fan would run at full RPM again. The only way I got around that was to never put the iMac to sleep, leaving it on all the time and only putting the display to sleep.

Samsung Electronics Samsung 840 Series Solid State Drive (SSD) 500 GB SATAIII 2.5-Inch MZ-7TD500BW

I got to thinking the other day that Apple probably didn’t read the HDD temperature by sending data from the HDD itself, but rather measuring the temperature of the jumper pins on the HDD, where the sensor plugged in.


I had an old HDD which didn’t work anymore and I removed the controller board from it because it had the IDE jumper pins on it. I took that and used some 3M 2-sided tape and stuck the controller board to the SSD and connected the temperature sensor cable to the jumper pins. I didn’t connect any power or anything else.

I put the iMac back together and turned it on, removed all my software tricks and scripts and restarted again. I went though all the events of startup, shutdown, restart, wake from sleep and wake on network access and never once did the HDD fan spin uncontrollably. It worked!

The fan stays at a speed of around 1100 to 1200 RPM’s and I figure the ambient temperature inside the iMac affects the pins a little and that’s what gives the various speed readings of the HDD fan. The dummy load HDD controller board from a dead HDD did the trick. It’s too bad for me that I didn’t think of this sooner, like 2 or 3 months ago.

Rebuild of iMac G5

Rebuild of iMac G5

I picked up an iMac G5 the other day from one of the girls at work. She acquired it from the GoodWill for $15. Apparently they thought it was an old television which is why it was so cheap.

She gave up the G5 to me because it kept powering off suddenly and/or wouldn’t power on at times.



I opened it up today suspecting blown capacitors in the power supply. Once I got it opened, my suspicions were confirmed upon looking over the PSU. I saw three capacitors who had blown their lids.


I ordered another PSU from eBay.


It had a 1GB RAM chip in it from Crucial so it appears that someone had added that at some point during it’s life. I ordered a second 1GB RAM chip from OWC today as well, bringing it to it’s 2GB maximum.



I then removed the 80GB WD HDD and ran Spinrite on it.



It only took 2 hours to complete compared to the 80 hours it took on my 1TB HDD from my 2010 iMac. No bad sectors were reported, so the HDD is in good condition.


I’m considering putting an SSD in it, but held off on ordering one until I do some more research on which one I should get first.

I really like how easy this G5 came apart over my 2010 iMac. I much preferred the G5’s rear backing coming off rather than the front so that I didn’t have to mess around with the display. Plus it was easier to get the panel off as well with just 3 screws to loosen.

Additionally, I was impressed at how clean the inside was for being an older computer. There was next to no dust inside it at all.

It’s fully updated with all Apple updates (10.5.8) and seems to be running fine.

I have SimCity 4 Rush Hour patched with 1.0.2 and it’s running just fine.

Overall, the OS is running okay, but with just a hint of choppiness. I think it’s because of having only 1GB of RAM. I will be looking closer at the RAM I bought to see what I did, because I think I got the wrong kind. Then I’ll order the proper RAM and get it running better.

I’m still looking into an SSD as well.


It’s current specifications are:

PowerMac 8,1
Model A1058
EMC 1989
Order Number M9248LL
1.6GHz PowerPC
17″ screen
Manufactured from August 2004 to May 2005

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