Charles Moore's Mailbag

Troubleshooting an iMac and Possible Pismo Overheating

Charles Moore - 2007.03.19 - Tip Jar

Problems Troubleshooting a Slot-loading iMac

From Steve:

Hi Charles,

Thanks for all your (compassionate!) advice to all of us forgotten low-end Mac users out here!

I just finally crossed over to Macs (again - I used to use Mac Pluses and SEs at my first job and loved them) and have been heartbroken to encounter a major system problem within a couple of days of getting my iMac.

I also have an interesting way that I am trying to solve it.

Care to take a look?

Here's my description of it:

  • I have an iMac (summer 2001)
  • I bought it secondhand with Tiger already installed; there are no CDs/DVDs
  • Installed two (supposedly) 512 MB DIMMs in it.
  • At first one came up as only 256 MB, then when I swapped them, the total was 1 gig
  • But then the screen got all sorts of coloured lines across it and the computer probably froze up (I didn't wait to see this before turning it off)
  • When I've tried to start the unit with both the new and the old memory, it has stopped at the grey screen with the turning wheel and got no further
  • I've tried many different types of starts, but nothing works
  • Interestingly, on the single-user start, the command prompt doesn't come up: I can't type anything
  • It also refuses to do a safe start

Other possible areas of interest:

  • When I first got the computer I noticed it would lose the time if it was unplugged, so I assume the battery is flat
  • Just before all these problems, at one point I changed the startup drive to start Mac OS 9 (in order to try a RAM-testing program). I also (pointlessly I guess), ticked for it to start OS 9 even if it actually started in Tiger. I guess the point of this was to get it to start OS 9 within Tiger if it actually failed to start in it.
  • I bought the unit secondhand, so I don't have the OS X startup disc - and can't easily get one
  • What I have done, though, is to pull out the Mac's drive and connect it successfully to my PC via a USB drive case, and am able to read it through Macdrive (cool, huh?)

I'm willing to buy Tiger again if I have to. There are some Aussies selling the DVD(s) on eBay. I know I could buy the CDs from Apple, but that would take ages!

I've also noticed a fairly affordable FireWire disk drive on eBay locally, but no affordable FireWire DVD-drives. (Will any make and model work with the Mac, or does it have to be for Mac especially?)

Any suggestions?

I'm heartbroken and lost!

- Steve

Hi Steve,

Sorry to hear of your troubles.

Did the iMac work okay before you installed the RAM upgrade?

Bad or substandard RAM could be part of the problem. My son once fried the motherboard in a Power Mac 9500 by installing bad RAM. In any case, revert to the RAM it had in it when you got it for the troubleshooting phase.

You really need some sort of bootable disk in order to vet out this issue, since it won't boot from the system on the hard drive. I would recommend getting an OS 9 disk and getting set up with it first (provided that you don't have a hardware problem. If it will boot from the OS 9 install CD (hold down the C key while booting) and mount the hard disk, then you know your basic hardware is functional. Install Tiger when/if you get it working with the Classic OS.

You should probably reinitialize the hard drive and start from scratch. I recommend partitioning the drive and putting OS 9 and OS X on separate partitions.

My guess is that most any FireWire device that doesn't require Windows-specific drivers should work with a Mac, but I can't guarantee it.


From Steve:

Just found an affordable USB DVD drive . . . could you boot an iMac G3 2001 from that?

Hi Steve,

No; pre-Intel Macs are not bootable (at least in practical terms) from USB.


From Steve:

Hey Charles - thanks for your extremely generous answer! You actually saved me $70 buying a USB DVD drive unnecessarily!

From Steve

Hi Charles,

Just a quicky! I do have a CD, but it is a set up CD specifically for an old Power Mac 7600. It appears to have an OS on it, but I figured that doesn't necessarily mean it will start in an iMac, because they are different hardware. When I put it in before, it did nothing.

So I was wondering, are there other (startup-type) tests I can do to rule out the worse-case scenario of the motherboard being fried?

For example, when I booted while hitting the option key, where it gives you the choice of boot drive, it does show a pic of a hard drive with the OS X logo.

I thought: Well if it had enough processing brain to do that, then perhaps the motherboard is okay? Interestingly though, it doesn't actually show OS 9. So maybe something is funny with the file structure or something.

What do you think?

(I really appreciate you taking time to reply by the way - know that in this hour of need it is particularly appreciated!)

Hi Steve,

It's pretty hard to troubleshoot without a bootable system. You need either a generic install disk or a System Restore disk for your particular Mac.

I suspect there is something amiss in the file structure. The appearance of the startup icon is a hopeful sign.

Have you tried booting into Single User Mode (hold down command-S at startup)? If this works, you will be in command line land, with a black background and a lot of code text.

If you get that far, at the localhost# prompt, type in fsck -y (make sure to include the space before the dash) and hit Return. That should initiate a disk check. If that doesn't work, try fsck -fy, which is supposed to force a disk check.

After the diagnostic routine, it will report whether it was able to find a problem and repair it. Sometimes it takes several passes.

Good luck.


Is My Pismo Really Overheating?

From Tom Gabriel:

Hi Charles,

I've got a strange possible problem with my Pismo G3 500 MHz PowerBook running OS X 10.3.9 & 9.2.2. It's never given me any functional problems whatsoever, but I occasionally check the CPU temperature by restarting in 9.2.2 and using Gauge Pro, which won't work in Classic mode - only 9.2.2 rebooted. In the past, it's been showing between 51-55° C, but last time it showed a temperature of 72° C, which for G3s should be frying time! (The fan hadn't cut in.) It also showed a CPU speed of 509 MHz and a system bus speed of 105 MHz!

Within 15 seconds or so, reported temperature went down to 64°, and CPU speed to 504 MHz, with bus speed at 102 MHz. Within a minute, it reported at 54° with CPU and bus speeds at the customary rates of 499.9 & 99.9 MHz respectively.

I don't know (a) what could be causing this sudden heating problem, or (b) if Gauge Pro is haywire and not reporting accurately, which I tend to suspect. I have 768 megs of RAM in it, the 512 stick labeled as PC100 but reporting in System Profiler as a PC133, yet I doubt this is doing anything to the CPU.

As I say, functionally it has always been fine, though this obviously worries me. The outer case is quite warm to the touch around the CPU & hard drive area, but not hot or uncomfortable if placed on the lap (I had it on a table with a smooth, hard flat surface when testing).

Do you or any of your other readers have any ideas on this? I'm mystified and a bit panicky! Thanks for any help you can give!

God Bless,
Tom Gabriel

Hi Tom,

If your Pismo is really running at 70° or more, it should feel pretty hot to touch, and the fan should definitely be cutting in.

My first suggestion would be to download Temperature Monitor (freeware) and run it in OS X 10.3.9, to get a "second opinion".

If Temperature Monitor also shows it's overheating, you may have some logic board component on the way out, or the fan thermostat could just be malfunctioning.


From Tom Gabriel:

Hey Charles,

I was installing a big update to the System software which had the hard drive working pretty hard, and the fan did cut in for awhile, then out when its job was done, so evidently that works okay.

I downloaded Temperature Monitor, installed it, and it told me it couldn't find any temperature sensors in the computer to read! Back to OS 9, and Gauge Pro told me temperatures in the 60s again (quickly quieted down to 50s)!

Well, I'm stumped, but it looks like the logic board component you referred to.

Don't know what else to think at this point.

Thanks for your help!


Hi Tom,

If it only happens when the processor is under extraordinary load, perhaps noting to worry about.


From Tom Gabriel:

Hi Charles,

I'd like to mention that I am very appreciative of how quickly you get back to me (and, I know, with your other readers) with feedback on an issue. It's totally professional and the mark of a conscientious writer.

Anyway, one last thing I did as a check on this whole issue, which I think points in the direction of the real answer: After operating the Pismo for 3-4 minutes, I rebooted into 9.2 and looked at Gauge Pro's reading. It was at 50° C, rapidly going down (10 seconds) to 42°. No Mac I have ever owned has ever gotten that warm that fast, and if it had, I could feel the warmth in the outer case, especially a laptop (er, notebook). The case felt completely cool to the touch at that point.

I think I've got Gauge Pro somehow messing up and reporting temperatures higher by fifteen-twenty degrees C than are actually present.

Anyway, as you advise, I'm not going to give it a whole lot of thought unless and until the Pismo starts acting up. And I'll soon invest in a hard drive that has a SMART temperature sensor (which my present original does not) so that I can use Temperature Monitor in X.

Thanks again for your input, I think we've probably got as close to the truth as we can!

Good Luck and God Bless,

Hi Tom,

FWIW, back when my Pismo still had its original 500 MHz G3 processor, it would typically run at 35° to 50° - usually at the lower end. I haven't found a temperature utility that can read the temp in the 550 MHz G4 upgrade, but it does run somewhat hotter with the G4. Daystar's replacement processor heat sink (copper instead of composite) helped significantly with keeping the fan silent, even running Tiger. That part would work with the stock processor as well.


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Charles Moore has been a freelance journalist since 1987 and began writing for Mac websites in May 1998. His The Road Warrior column was a regular feature on MacOpinion, he is news editor at and a columnist at If you find his articles helpful, please consider making a donation to his tip jar.

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