Troubling iMac

-


A few months ago I bought a shiny 20" iMac. While the initial impression was good, I was not happy after the trouble I had installing Leopard and certain incompatibilities it brought.

Just when it seemed things were settling down I've got the system just dying on me after opening a large (120MB) PDF file. The screen turned black and then the system rebooted spontaneously. Another computer was on at the same time and it did not experience any problem, so I do not think that was because of a power spike.

Today, when I started the system there was a multilingual message in a centered dark square telling me to press the power button for several seconds to shutdown the system (neither the keyboard or the mouse worked). I have never seen that image before (but I failed to take a photo), it contained the message in Japanse too. It happens to be an OS X kernel panic.

When I powered on the system again I heard the welcome sound and next two beeps and then three beeps that repeated over and over again. It did not sound good. A quick check on the net (using other computer, of course) showed that 2 or 3 beeps signal RAM memory trouble (mine is the original RAM that came with the system and because of the cool and compact format of iMac is not user serviceable).

I removed the computer power cord for some seconds and then I connected it back to try again: No changes, same sequence of sounds; no joy.

Having nothing to lose I removed the power cord again and I applied some of my frustration through my hands (i.e. more than gentle taps to the system). After reconnecting the power the system booted up as normal. My guess is that the RAM is not properly seated on the socket. I'll be paying attention to see if something weird happens again.

Now I'm going to hunt for some memory test software.

Update: Thanks to Jesus coments (and this page) I realized I was wrong: My iMac does have two memory slots that are easily accessible by the user by removing two screws on the bottom part of the screen. Not sure the trouble was caused by memory though, as several diagnostic attempts gave no indication of memory faults. Anyway, if the problem happens again now I know I can access the system's RAM memory.

Comments

Hiroshi Ikeda said…
This seems related to a hardware problem, maybe memory, maybe hard disk. Anyway give a try to the Apple Hardware Test (it's in one of the systems cd, boot with the cd on the iMac pressing the C key or the Alt key).
Good luck.
10:44 am
misan said…
Thanks a lot.

I'll try this out.

I do not think I'm buying another Mac anytime soon though.
11:48 am
Unknown said…
Hello Miguel:

What a bad luck!!!

Try the hardware test...

It sounds a memory problem....

Jesus
12:03 am
misan said…
When I made my buying decision I was a bit frighten of buying a computer with no user serviceable parts.

Now my worst fears seem to have become true.

Re-sitting (or replacing) RAM memory takes 5 minutes and no skills on another computer, but opening an iMac is a bit of a challenge (I do not have the suction cap yet) and it voids your guarantee.

It is said that good judgment comes from bad judgment :-)
12:18 am
Unknown said…
Hello again:

To reseat (o replace) the computer memory, you must only work in two screws...It is no necessary to open all the computer...The screws are located under the screen...

If you want to open the new imac then it is no easy and (as you tell), you need the suction cap to remove the main screen glass...

Jesus
4:01 pm
misan said…
Unfortunately the only RAM in my iMac is the factory-installed 1GB SODIMM located inside the guts. The extension socket in the bottom of the screen is easy to access but empty at the moment.

Anyway, after discovering diagnostics on OS X 10.4 install disk are obtained by pressing D key, the system seems quite happy about the memory. Both the long and the short memory test agree that memory is now working properly.

I'll keep my fingers crossed (and maybe I'll look for that suction cap once the guarantee period is over :-)

Thank you for all your help.
4:30 pm
Unknown said…
Hello Again:

Are you sure of that?

I was looking for how to change the RAM slots in your computer and I found this from Apple web site

http://docs.info.apple.com/article.html?artnum=306204

You can see that your computer has 2 slots

It seems (but I am not sure) that you have an empty slot and a slot with 1 GB of RAM.

Please check this, because if you read the Apple document carefully, it talks about how to change your RAM or HOW TO REPLACE IT

I think that all the RAM is user serviceable (but not the graphic card)



Jesus
6:05 pm
misan said…
You are absolutely right. All system RAM is user accessible. I did not know that because I never opened the memory cover before. Somehow I assumed that like a laptop the memory it comes with was inside the "difficult" area.

I have updated my post accordingly too.

Thanks a lot for the help,

Miguel
6:18 pm
Unknown said…
Hello again:

I'm glad to hear that...

In fact, in my Mac (an Imac Late 2006), two screws must be unscrewed. In your Mac, it is necessary to unscrew only a screw

About, the laptops...Apple laptops have the same system several years ago...

As far as I know, now the only Apple computer with memory no serviceable is the MacMini...I have a Mini, and I bought with 2 Gb of RAM (not from Apple, because is too expensive ) to avoid any opening problem.

If you want to open your Mac, check this:

http://www.kodawarisan.com/imac_2007_mid/imac_2007_mid_01.html


Jesus
7:09 pm
Unknown said…
Hi again:

I forgot it :) , the new Macbook air has also a non serviceable memory
7:25 pm
Post a Comment

Popular posts from this blog

VFD control with Arduino using RS485 link

-
Image
Variable Frequency Drives ( VFD ) allow the control of spindles so speed can accurately be controlled and a detailed acceleration profile for the spindle and reverse rotation can all be handled. In essence a VFD is an three phase inverter for three-phase AC motor. I am using a popular (I mean cheap) Chinese VFD and though the reference manual is not great, I could see there is a built-in RS-485 port. I usually control the start, stop and speed selection using the keyboard on the unit but I thought it will be more useful if I could control everything from the same Arduino is doing our CNC table control. Some cheap RS-485 off eBay and some lines of code later, I can start, stop and change the speed from an Arduino. What a cool thing to have! Some configuration of your VFD are needed before you can use it like that.  You need to set PD163=1 (I am using address 1 in the code). PD=164=1 (for setting serial to 9600bps) and PD165=0 (for using ASCII and 8N1 character format)
Read more

How to get sinusoidal s-curve for a stepper motor

-
Image
After some experimentation, and delving a bit into the math of motion, I realized there can be a significant difference on the motion of a machine by just making small changes. A common and popular approach to smooth one axis of motion is to use a trapezoidal speed pattern, where acceleration and deceleration are uniformly accelerated movements (aka constant acceleration motion) separated by a portion happening at cruising speed. The problem comes with the fact that, while that approach is simple to understand and to code, it does contain sudden changes in the acceleration, that show as spikes on the acceleration derivative, called jerk. These sudden changes in the acceleration translate into undesired vibration in our machines. Most of that can be eliminated by selecting a motion pattern that does not contain sudden changes of acceleration. If we chose a mathematical function for our speed whose second derivative is continuous, then we reduce system vibration quite a lot. One ma
Read more

Stepper motor step signal timing calculation

-
Image
While we use stepper motors in many devices, the timing of the step signals is not always well understood. Most of us can see how a fixed speed is a bad idea unless the speed of motion is really slow, but it is fixed speed what is really to generate with simple code. You just can use the Arduino Blink example to send a fixed frequency of pulses to a stepper motor driver. If too slow, just reduce the delay value. But for most real-life applications variable speed controls will perform better. These systems will speed up the motor to a given maximum speed and it will slow it down to stop at the desired step count. But understanding the math behind this process is sometimes not obvious. Let us start with the simple case of the so-called trapezoidal speed motion profile. Here motion takes place in three phases: acceleration, constant speed (cruising) and deceleration. But the point is how can our code create such a behavior. Stepper motor drivers usually accept two signals to control
Read more