iMac not starting up (no chime and no USB power)

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Level 1

36 points

iMac not starting up (no chime and no USB power)

Hello,

My neighbor's computer is experiencing some problems: it does not start (the screen stays black, no startup chime, but the fans run, as does the hard disk. Also, neither the mouse or the keyboard seem to be powered (no light), so the computer doesn't even come to loading the EFI). The model is an iSight iMac G5 20'' (EMC=2082).

I have tried usual commands (reset PRAM and reset the SMC). Also tried with no device connected. (well, if something so trivial than all these tips did the trick, I wouldn't had to ask here ).

So, without keyboard, I couldn't even try special modes (safe, target disk, start from CD, etc), should the Mac be able to start in some mode. I have then decided to open the iMac (well, the warranty is way out, so nothing is lost). I have never seen a so-hard-to-open Mac, by the way (something was likely blocked).

I'm thinking of 4 possible causes for the problem:
-the hard disk could be damaged. It was malfunctioning some days ago. I assume it could come to a point where the logical board of the disk is failing;
-the RAM is an obvious possible cause;
-the CPU is also obvious;
-another component on the main board/logic board.
-I have forgotten a 5th point?

Well, I tried with unplugging the hard disk, and it had no effect, so it's not the HDD. I'm puzzled for the remaining ones (not knowing the iMac enough is a cause).

First, about the RAM, it seems the RAM slot is empty, so the actual RAM is somehow built-in (I haven't seen something seeming like usual RAM bars), so, if I can't remove the RAM, how can I test whether it's damaged or not?

Then, the CPU. There are 2 of them. So I thought I may take one out (and then the other one) and see whether the Mac starts. Well, I can't figure out how to remove the CPU cooling piece (there are just 4 "buttons" that can be pressed but nothing happen). I prefer asking here first, not removing the entire main board without advices.

Lastly, if it's the main board, I know I won't be able to do much. I have read there are LEDs to possibly diagnose power issues, but I don't see them (no LED is showing light, it seems). I'd like to test my other assumptions before thinking the main board is the cause.

Else, is there something I could try I have forgotten?

P.S: sorry for my (possibly) bad english, and the troubles of explanation; it's not as easy when english isn't the native language. I just wanted to mention that I have already repaired computers, so don't hesitate to tell me complicated answers.

Thanks in advance for your help.

MacBook Pro, Mac OS X (10.5.1)

Posted on Feb 12, 2010 9:49 AM

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Answer 1

Top-ranking reply

Anic264b Author

Level 1

36 points

Feb 13, 2010 9:18 AM in response to spudnuty

spudnuty wrote:
Anic,

Also, neither the mouse or the keyboard seem to be powered (no light),

First you might try booting without any USB devices connected.

Well, we sort of tried that (while the Mac was open, with no device connected, we switched it on several times: it didn't started up either).

I tried with unplugging the hard disk, and it had no effect

So you already have it open.

Yes, hardly, but yes. I already did what I learnt in "high school", except the RAM which seems to be hardly testable.

the CPU. There are 2 of them.

Hmm there's only one actually under the large shroud and heat sink with the large fan and a small one at bottom.

So I thought I may take one out (and then the other one) and see whether the Mac starts

Well don't bother since it's not removable without professional rework equipment.

So it seems nothing can be tested on that model? You can't remove the CPU nor remove/replace the RAM… Really a bad model! (still, I like Macs, but that's amazing…)

I have read there are LEDs to possibly diagnose power issues, but I don't see them (no LED is showing light, it seems).

OK the LEDs are under tape. From the service manual:
"13. Locate and peel up the small piece of black tape near the bottom of the logic board.
14.Under the black tape you’ll see the four labelled diagnostic LEDs...
LED 1: Indicates that trickle voltage from the AC power inlet to the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.
LED 2: Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.
LED 3: Indicates that the main logic board has established communication with the LCD display.
LED 4: Indicates a processor over-temperature condition. The system will shut down when this LED turns on."

Ah, yes, I've discovered them.LED1 and 2 are correct (LED1 is on when the computer is plugged and LED2 when the power button has initiated the start up). LED3 is always off, which reveals there's something wrong beyond just the display. LED4 is off, expectedly.

Be very careful when working with the front off since the power supply is exposed and high voltages are present.

Thanks. I indeed never touch a board when the computer is plugged.

There are two elements to the power supply: the supply itself and the DC - DC board."

Thanks, I have located them.

Email me if you need more info.

Actually, it's the info about which info I need that I'm looking for 😉
After having tried what I could, the remaining bits seem locked (unlike other models).
Thank you for your suggestion.

Oh did you try an external display?

Well, my neighbor does not seem to have the external screen adaptor. Perhaps it was optional in the purchase? (if it wasn't optional, then she does not know where it is).

I have a question regarding this: I guess the LED3 is concerning the whole graphic card, not just the built-in output, right (in other words, not just about the "main" display)? So I doubt an external screen would make any difference since the LED3 is off (tell me if I'm wrong).

It could also be a GPU chip problem. I've got a 20" iSight here taken apart. It has a bad GPU chip and the logic board is currently out for a swap of that chip.

Sadly, I have learnt computers (hardware parts) on PCs (I had not choice of learning on Macs, except at home). Now, that's true there are differences.

Two questions come from your phrase:
1: should a bad GPU not prevent just the graphics to stay black (so to say, the keyboard would still power on and the computer start anyway)?
2: how do you diagnose a dead GPU if the Mac can't even start the Apple Hardware Test? Do you actually measure the voltage on the GPU's connectors to see it's wrong? (I have no idea which connectors and values I should measure).

Thanks for your answer. I'm always happy to learn things!

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Answer 2

spudnuty

Level 5

7,128 points

Feb 13, 2010 11:29 AM in response to Anic264b

Anic,

You can't remove the CPU nor remove/replace the RAM… Really a bad model!

Yes you have to think of it more like a laptop. The only models w/ removable CPUs were the Towers.

Thanks. I indeed never touch a board when the computer is plugged.

Hee hee I did since I was used to working on the ALS model where the power supply is enclosed.

Actually, it's the info about which info I need that I'm looking for 😉

After having tried what I could, the remaining bits seem locked (unlike other models).
Not sure what you mean here?

the external screen adaptor..(if it wasn't optional, then she does not know where it is).

Well it looks like this. It's pretty standard. Every iBook had one for instance.
http://www.synaptech.com/catalog/images/922-4554.gif

I have a question regarding this: I guess the LED3 is concerning the whole graphic card, not just the built-in output, right (in other words, not just about the "main" display)? So I doubt an external screen would make any difference since the LED3 is off (tell me if I'm wrong).

Well what the manual says is:
"LED 3: Indicates that the main logic board has established communication with the LCD display."
So if that's not light then the graphics chip is not communicating with LCD panel.
So you did a SMU reset like this:
"Resetting the SMU (System Management Unit)
1. Unplug all cables from the computer, including the power cord.
Wait 10 seconds.
2. Plug in the power cord while simultaneously pressing and holding the power button on the back of the computer.
3. Let go of the power button.
4. Press the power button once more to start up your iMac G5 (17-inch iSight).

If that doesn't help you really need that Mini VGA to VGA adapter so you can plug in a standard VGA monitor and check out the output of the graphics chip (GPU).
Since it's not communicating with the LCD it could be a cable problem.
Also you should read through this site:
http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php
Which concerns the "capacitor plague". I'm sure you're aware of this. We had 30 Dell P-IVs that had this problem and those logic boards had a ton of lytics on them.

As to the rest of your questions, answer this set first.
Richard

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Answer 3

spudnuty

Level 5

7,128 points

Feb 12, 2010 9:08 PM in response to Anic264b

Anic,

Also, neither the mouse or the keyboard seem to be powered (no light),

First you might try booting without any USB devices connected.

I tried with unplugging the hard disk, and it had no effect

So you already have it open.

the CPU. There are 2 of them.

Hmm there's only one actually under the large shroud and heat sink with the large fan and a small one at bottom.

So I thought I may take one out (and then the other one) and see whether the Mac starts

Well don't bother since it's not removable without professional rework equipment.

I have read there are LEDs to possibly diagnose power issues, but I don't see them (no LED is showing light, it seems).

OK the LEDs are under tape. From the service manual:
"13. Locate and peel up the small piece of black tape near the bottom of the logic board.
14.Under the black tape you’ll see the four labelled diagnostic LEDs...
LED 1: Indicates that trickle voltage from the AC power inlet to the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.
LED 2: Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.
LED 3: Indicates that the main logic board has established communication with the LCD display.
LED 4: Indicates a processor over-temperature condition. The system will shut down when this LED turns on."
Be very careful when working with the front off since the power supply is exposed and high voltages are present.
There are two elements to the power supply: the supply itself and the DC - DC board."
Email me if you need more info.
Oh did you try an external display?
It could also be a GPU chip problem. I've got a 20" iSight here taken apart. It has a bad GPU chip and the logic board is currently out for a swap of that chip.

Richard

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Answer 4

Anic264b Author

Level 1

36 points

Feb 14, 2010 12:16 PM in response to spudnuty

spudnuty wrote:

Hello,

Anic,

You can't remove the CPU nor remove/replace the RAM… Really a bad model!

Yes you have to think of it more like a laptop. The only models w/ removable CPUs were the Towers.

Which explains why I thought CPU were usually removable (I have mostly used towers except the original iMac, before).

Thanks. I indeed never touch a board when the computer is plugged.

Hee hee I did since I was used to working on the ALS model where the power supply is enclosed.

Even on an enclosed power supply, I'd not want to touch some kind of board. Well, perhaps it's just me.

Actually, it's the info about which info I need that I'm looking for 😉

After having tried what I could, the remaining bits seem locked (unlike other models).
Not sure what you mean here?

Well, after re-reading myself, I agree I don't really understand either 😉
I meant that I have already tried as much as I could, but the remaining bits (so to mention, the RAM and CPU, mainly) can't be tested. So, I'm looking for testing other parts of the iMac (perhaps there's other things that can be tested, like flashing the EFI).

I'd like to hear from you that the built-in RAM can't be tested, please (to clear my assumption).

the external screen adaptor..(if it wasn't optional, then she does not know where it is).

Well it looks like this. It's pretty standard. Every iBook had one for instance.
http://www.synaptech.com/catalog/images/922-4554.gif

In fact, all the laptops I have seen have that kind of adaptor (although they may slightly vary from models to models), but I thought it was only for laptops (which, as they are easy to move, may have different available screens). Now, does it also apply to iMacs?

I have a question regarding this: I guess the LED3 is concerning the whole graphic card, not just the built-in output, right (in other words, not just about the "main" display)? So I doubt an external screen would make any difference since the LED3 is off (tell me if I'm wrong).

Well what the manual says is:
"LED 3: Indicates that the main logic board has established communication with the LCD display."
So if that's not light then the graphics chip is not communicating with LCD panel.

Fine, but can the graphics chip still communicate with the external port, even if the LED3 is off?
(sorry for having been unclear)

So you did a SMU reset like this:
"Resetting the SMU (System Management Unit)
1. Unplug all cables from the computer, including the power cord.
Wait 10 seconds.
2. Plug in the power cord while simultaneously pressing and holding the power button on the back of the computer.
3. Let go of the power button.
4. Press the power button once more to start up your iMac G5 (17-inch iSight).

Hmm… Not sure about step 2. The "simultaneously" part may not be what I did (I actually tried two things:
1: plugged back the power cord, then (after that) pressed the power button
2: while still unplugged, I pressed the power button (held down for about 5 seconds), then released it and plugged the power cord back.

Do you think I should press the power button while the iMac is still unplugged and keep the button pressed while I plug the iMac (then release the button after I have plugged it)?

If that doesn't help you really need that Mini VGA to VGA adapter so you can plug in a standard VGA monitor and check out the output of the graphics chip (GPU).

I'm glad you mentioned every iBook has one, since my sister has an iBook 🙂
I'll ask her.

Since it's not communicating with the LCD it could be a cable problem.

I'm doubting of that, because I'm sure the Mac does not boot at all (not just a blank screen, but also no power on USB ports).

Also you should read through this site:
http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php
Which concerns the "capacitor plague". I'm sure you're aware of this. We had 30 Dell P-IVs that had this problem and those logic boards had a ton of lytics on them.

Hmm… What a charming surprise 😉
Well, I'm indeed aware of this (it hasn't happened to me yet, fortunately).
Thanks for the link.

As to the rest of your questions, answer this set first.

Fine, I follow the guide 😉

Thank you.

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Answer 5

Feb 12, 2010 11:27 AM in response to Anic264b

Except for RAM installation, the iSight G5 iMacs are NOT user repairable. 😟 Parts for same are not made available to the public. 😟 However, all is not lost. If you do a Google search, you may find a few in the wild. Check out: Mac G5 Parts & Repair Services

Regarding the RAM slots, check out KB Article: http://support.apple.com/kb/HT2266 iMac G5 (iSight): Installing and replacing memory (RAM)

Also check out: iMac G5 (iSight Model) Take Apart Instructions

Good luck! You're going to need it.

!http://i45.tinypic.com/jl0z95.jpg!

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Answer 6

Mar 15, 2010 7:44 PM in response to Anic264b

Anic,

Sorry I am new this post Hopefully it is legible. I am having the some of the same problems with one of my imacs(20" isight g5 2.1) and was wondering if you ever found a solution to your problem? My symptoms are almost exactly the same.

Upon turning the computer on I get LED#1 & 2 to light up correctly than seconds after that, LED#3 & the LCD flash's simultaneously three times very quickly then it stays lit as it should. After the three flashes the screen appears to be on but has a reddish tint to it(more visible at an angle rather than looking straight at it). LED's 1-3 stay lit as they should but no chime and no gray screen(video). Two of the three fans turn on immediately upon turning on, then shortly after, the fan in the center of the logic board between the heat sinks kicks on.

I haven't checked the usb ports but I have tired a pram reset The only reset I haven't tried was the (SMU) reset button on the back side of the logic board, partly because it is impossible to get to without I assume pulling the logic board half way out while it is plugged in.

While inspecting the board after taking it out I did notice two bulging capacitors (6.3vlt 1800uf). Which I replaced. But still no progress. I did however purchase a complete cap kit for the imac with plans of replacing all f the caps with hopes of one that visually might not be bad...

And last but not least I pulled all heatsinks and cleaned and replaced all of the thermal paste.(Still no progress)

Have you tried pulling your logic board and inspecting the capacitors? This seems to be a pretty common problem for g5 imacs. I have had issues with a number of imacs doing these things and have resolved the issues simply by replacing caps.

I just don't know what is wrong with this g5 20" isight. Seems they have more problems than non isight g5's

Let me know if you have found a solution or any of the trouble shooting I mentioned above helps

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Answer 7

Anic264b Author

Level 1

36 points

Feb 17, 2010 3:47 AM in response to spudnuty

spudnuty wrote:
Anic,

I'd like to hear from you that the built-in RAM can't be tested, please (to clear my assumption).

Well it can be tested but I don't think this is your problem as you'd get error beeps at startup.

Yes, it's also what I think, but I wondered if the speakers could have been deactivated (like for instance, on some models, if you turn off the sound volume while using the computer normally, the startup chimes also deactivates).

Yes since it won't start it can't be tested. Maybe via Apple hardware test or a test disk available only to technicians.

That's a shame. There was not such a concept in MacOS 9 days (anyone could do anything to repair his Mac; no CD available only to a subset of people 😟

Fine, but can the graphics chip still communicate with the external port, even if the LED3 is off?
(sorry for having been unclear)

Maybe depending on what's wrong.

Yes, so it's not a problem specific to the screen cables or graphics card.

Hmm… Not sure about step 2. The "simultaneously" part may not be what I did (I actually tried two things:

No you have to follow that exactly. The plug in and the holding of the power button must be done at the same time. So follow those steps exactly.

Ok, now I have done this. At first, I thought it worked, but it's not. In fact, I've learnt something more: the USB ports are actually powered fine, unlike what I thought. At first, the mouse was plugged in the keyboard and the keyboard in the computer; neither the mouse nor the keyboard worked. Yesterday, I tried with the keyboard and mouse in separate ports on the computer (so the mouse was not plugged in the keyboard) and have discovered the mouse lights on but not the keyboard. So it appears the Caps Lock key does not light on as easily as the mouse does (it's certainly part of the problem, the USB ports are actually powered, but the bit that makes the keyboards' caps lock lighting hasn't loaded). Does it actually remove a possible problem?

I'm doubting of that, because I'm sure the Mac does not boot at all (not just a blank screen, but also no power on USB ports).

I think this is a thing that happens that's new with this model. If the GPU doesn't communicate with the LCD the boot just stops.

Thanks for your help so far.

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Answer 8

spudnuty

Level 5

7,128 points

Feb 14, 2010 1:05 PM in response to Anic264b

Anic,

I'd like to hear from you that the built-in RAM can't be tested, please (to clear my assumption).

Well it can be tested but I don't think this is your problem as you'd get error beeps at startup. Yes since it won't start it can't be tested. Maybe via Apple hardware test or a test disk available only to technicians.

In fact, all the laptops I have seen have that kind of adaptor ... Now, does it also apply to iMacs?

Yes it's the same adapter.

Fine, but can the graphics chip still communicate with the external port, even if the LED3 is off?

(sorry for having been unclear)
Maybe depending on what's wrong.

Hmm… Not sure about step 2. The "simultaneously" part may not be what I did (I actually tried two things:

No you have to follow that exactly. The plug in and the holding of the power button must be done at the same time. So follow those steps exactly.

I'm doubting of that, because I'm sure the Mac does not boot at all (not just a blank screen, but also no power on USB ports).

I think this is a thing that happens that's new with this model. If the GPU doesn't communicate with the LCD the boot just stops.

Richard

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Answer 9

spudnuty

Level 5

7,128 points

Feb 20, 2010 8:07 AM in response to Anic264b

Anic,

.... actually it's free.
Seriously? You certainly have to subscribe somewhere, don't you?

I meant (tongue in cheek of course) that the diagnostic tests are free to Mac techs after you've paid for the training to become a tech.

I thought it was the third LED that indicated the communicating with the display, isn't it? The first LED for powered mainboard, the 2nd one for turned-on mainboard, but I don't have the 3rd LED on (so no communication with the display).

Right what I should have said to be more precise:
"With two of the LEDs lit that's saying its fine up to the point where it (communicates) _starts to communicate_ with the display."
But you still need the external display to tell us what's going on.
Richard

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Answer 10

MGW

Level 7

27,047 points

Feb 12, 2010 1:48 PM in response to Anic264b

Try contacting [synaptech.com], they are very knowledgeable and helpful (I am assuming you are in the US, if not, it would be useful to know where you are).
Look here for some clues:

http://www.kodawarisan.com/imacintel/imacintel01.html
http://xlr8yourmac.com/systems/imacisight_internals/imac_g5_isightinside.html
http://nl.youtube.com/watch?v=iVgL9u7ySUk
http://nl.youtube.com/watch?v=fI_QmBueWg4&feature=related

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Answer 11

Anic264b Author

Level 1

36 points

Feb 12, 2010 2:44 PM in response to MGW

MGW wrote:
Try contacting [synaptech.com], they are very knowledgeable and helpful (I am assuming you are in the US, if not, it would be useful to know where you are).

Hmm... It seems there are things I should have mentioned in the first place, sorry for having missed them. I'm living in Switzerland, it's not really a neighbor country (haven't you seen my english weakness in my sentences? 😉 )

Look here for some clues:

http://www.kodawarisan.com/imacintel/imacintel01.html
http://xlr8yourmac.com/systems/imacisight_internals/imac_g5_isightinside.html
http://nl.youtube.com/watch?v=iVgL9u7ySUk
http://nl.youtube.com/watch?v=fI_QmBueWg4&feature=related

Thanks for these links. I'm currently watching them.
I'm not sure they will help me in isolating the problem thought (I have already successfully opened the iMac, while it was hard). Well, I continue watching to see if there's more.

If you have some further hints, I accept 😉

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Answer 12

Feb 13, 2010 7:59 AM in response to Anic264b

Check out YouTube - http://www.youtube.com/watch?v=FN3N_qxLlWk

!http://i45.tinypic.com/jl0z95.jpg!

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Answer 13

Anic264b Author

Level 1

36 points

Feb 12, 2010 12:48 PM in response to Baby-Boomer-USofA

Baby Boomer (USofA) wrote:
Except for RAM installation, the iSight G5 iMacs are NOT user repairable. 😟 Parts for same are not made available to the public. 😟

Well, take, for example, the hard disk. It certainly is user repairable. I agree with you, however, that the built-in RAM is a hard concept for anyone who wants to test the RAM.

There are 2 ways to understand "there is nothing user-repairable", in my opinion: either it's a personal opinion (you tried it yourself and you couldn't repair, even something that is repairable on another model/computer), or Apple's opinion. While I love Apple since 15 years, their policy of "hiding" things and making non-user-repairable things is a little annoying to me (I'm someone curious who like to understand things, so it's the reverse of that policy). Since the warranty is way out, I want to do whatever I can do repair her Mac. But I can't do that without asking for help here (I know many basises, but it's beyond basises here).

However, all is not lost. If you do a Google search, you may find a few in the wild. Check out: Mac G5 Parts & Repair Services

The link is down 😟
What do you suggest me to search for? I have spent the last 2 days in googling but all the pages I have seen are concerning others models of iMac. If I search for something too specific (e.g iMac G5 20'' iSight white repair) then I get either nothing or not what I want.

Regarding the RAM slots, check out KB Article: http://support.apple.com/kb/HT2266 iMac G5 (iSight): Installing and replacing memory (RAM)

Sadly, the only RAM that I want to check is the built-in one. The external slot was empty (and I even already tried inserting some RAM in there, but same result). And this article does not seem to tell I can test the built-in RAM.

Also check out: iMac G5 (iSight Model) Take Apart Instructions

Hmm… This is also a page I have already visited (though, I haven't searched further into the links).

Good luck! You're going to need it.

Thanks. For the moment, I'm tired of debugging (spent the last 2 days in trying various things but nothing worked so far; I even tried removing some internal boards). I know it can be the mainboard's fault, but I want to remove every other possible cause before. For now, I need a way to know what's wrong (if it was the RAM, the LED would blink, wouldn't it?).

Thank you for this answer.

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Answer 14

MGW

Level 7

27,047 points

Feb 12, 2010 3:30 PM in response to Anic264b

haven't you seen my english weakness in my sentences?

Lots of people living in the States speak less than perfect English. In any case, it would be a good idea for you to go to your Settings and enter Switzerland.

Let us know if any of the links are helpful, they are not country-dependent.

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Answer 15

Anic264b Author

Level 1

36 points

Feb 13, 2010 8:53 AM in response to MGW

MGW wrote:
Lots of people living in the States speak less than perfect English. In any case, it would be a good idea for you to go to your Settings and enter Switzerland.

Ok, I'm doing it right now.

Let us know if any of the links are helpful, they are not country-dependent.

For what I've seen, some aren't useful (I already tried this). Others are more difficult as I only write in english (pronouncing is done in french in my head; I understand a lot, but some keys may be missed).

Thanks

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