Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

[sylphhawkins]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Hey Keebler64,

Thanks for the notes on reflowing the GPU with the alum shield and heat torch method. =),
I've come to the conclusion that I well fried the original GPU card after doing an oven reflow and getting distracted, =(, "woops", =p
still, I ended up finding a cheap HD 2600 GPU card on ebay (pulled working from a working iMac with LCD screen damage).

I popped that in and after a bit of fiddling, (I think I might have tried reseating RAM, scrubbing the DIMM slots with a toothbrush with methyl spirits to really clean the terminals, etc..)

The iMac seemed to buzz back to life!,
I used it totally fine for about 2 weeks, put a new 1tb HD in it, and dual booted it, and it was running flawlessly.

I had iStat menu's installed, and was monitoring the temps and voltages constantly.

I initially found that there was a little bit of strange behaviour with processing and some glitches, but it never froze completely.
I wondered if the 0.91v for the CPU cores was a bit too low for what it was wanting for stability, so I disabled 1 of the cores, (which seemed to set the voltage for the active core to a default of 1.17v, and it never really moved from this).

Initially, after disabling one of the CPU cores, the iMac ran like a dream!, =)
I even spent hours on it back and forth between OSX and Win XP jailbreaking and unlocking my iPhone!, ^_^

...

Then, after about 2 weeks, some of the funny old symptoms returned,
it began to freeze and lock up during use, then over just a few hours, it returned to how it was when I started, no boot, no chime, sometimes it will boot to OSX loading grey screen if I mess around with SMC resets and PRAM resets, but it always freezes within a minute or 2 of booting.

All I can think of is that either:

a) The GPU was the cause of the problem, and the new (used) one fixed it, until it too started to suffer the same issues?, it never seemed to be overheating from the temps on iStat, but the fact that it ALWAYS showed 0.00v and 0.01amp in iStat's voltage measuring worried me.

or

b) That the problem was never really "solved", and that some broken or faulty component became "happy" again for a short time (either through heat related issues deteriorating it, or perhaps a physical bump/moving/cold solder joint kind of issue?


Strangely though, when it was suddenly working like a dream (I even put it all back together, thats how working it was, =p)
I thought that it might have been a fragile thing, so I tried all sorts of things to upset it. I.e., physically moving it, shaking it, tapping it while running, shaking it while it was running hot (don't worry spinning Hard Drive fans, I had it booted from an external at this point, and the internal drive disconnected =p), running it through various test procedures, benchmark rendering and hard processor tasks, and it flew through them all like a breeze!

- I think that I might try removing the GPU card again, and seeing if it will boot, chime + log into OSX, to see if I can SSH in and screen share it, to see if it is stable again.


If it is, it is definitely pointing to some kind of GPU issues which cause the system to freeze (not just display connection, file sharing drops out, itunes music crashes/loops on the millisecond that it was up to in the song (like a scratched CD), etc.., so what ever is getting tripped, trips the whole system.

Grrr*

[sylphhawkins]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

*UPDATE*

Hi again,
I wanted to quickly update everyone who's following this thread, with "yet" another note about the iMac 7,1 20" 2.4Ghz repair.

I had put it aside for a while, to work on fixing up my new present I bought myself (a water damaged (or should we say, coffee damaged) Macbook Pro 15" 2009 that I found on ebay super cheap, ^_^), and now that that's up and running superbly (I'm writing this post on it right now), I decided to crack open the iMac and look over it again.

Straight up, I started off with the same thoughts as when I last looked at her, I was suspecting the GPU (as I have already replaced the CPU with a know working one, and there was no change).

Through fiddling I managed to get the iMac to chime again, and boot to the apple logo, spinning gear, when I noticed some dust on the northbridge heatsink (the one staring at you when you open up the iMac, with the ambient light sensor mounted on it).

What happened, was an immediate freezing of the spinning gear.
I tried turning it off and on again to test it, and I could get it to freeze, by lightly pressing or knocking the northbridge heatsink.

I pressed it down pretty hard to the right, and the next boot went perfectly, allowed me to install OSX 10.6 again (to test it out), and all was seemingly running well, until after a few hours, it was back it's freezing games.

After this unexpected "whoo hoo", no amount of pressing the heatsink would make a difference (I wondered if the BGA of the northbridge chip might have been damaged from the overheating (similar to the Xbox RROD problem), so I stripped off the heatsink and cleaned up the stupid amount of old caked on thermal paste (which had mashed out across most of the chip's SMD capacitors). After putting the heatsink back on, and trying to boot it up, nothing had changed.

This time, I thought I'd try the same thing as an Xbox 360 fix I did, and replace the heatsink mount "stoppers" with actual bolts, washers and nuts. I tightened it down, and turned it on and some interesting things happened.

a) None of the fans would spin (at least this confirmed that the fans and boot sequence are probably run/initiated by the Northbridge chip)

b) the DVD drive would spin up, and I could hear the laser moving and reading,

c) Still no display, no LED 4 status light, no boot chime.

I wondered if perhaps the SMD caps on the northbridge chip were shorting out on the heatsink?, so I removed the heatsink all together, and started it up.
It chimed, fans ran, and got half way through booting when it froze again, as usual, with the spinning gear.


This has made me wonder though, if perhaps the Northbridge chip (which, reading from the markings on the die, says that it is an intel chip SLA5U made in '06') has a part to play in all these problems?.

Since pressing down the extra pressure on the chip didn't help, i'm going to try to gently reflow it specifically, and see if it helps the iMac get back to life?

- Sylph

[sylphhawkins]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Hoho!

To everyone who is watching this thread about the iMac 7,1 repair.

I seem to have been able to isolate my problems (and the repair ^_^ ) down to the Northbridge chip. On this model (a mid-2007 iMac 7,1) the northbridge chip is an Intel SLA5U.

Removing the heatsink and performing a quick DIY reflow of the chip (I used an old tea-light candle tin cup filled with methyl spirits, and set it alight with the imac powered on, to heat up the northbridge chip enough to reflow the solder BGA balls underneath).

*******
P.S. - This idea comes from the "DIY reflow iBook G4 GPU" idea, and I'm aware of the risky implications of heating the northbridge chip itself to reflow the solder, so please do not reply with negative comments about the technique. ^_^
*******

Once the methyl spirits had finished burning (been used up), I turned off the imac and allowed it to cool for an hour.

Powering it back on, and the iMac booted and chimed fine!, ran flawlessly for hours. Booted into OSX 10.6, then bootcamped and installed XP, ran windows fine.
I left it running for over 12 hours over night, and it jumped straight back to action the next morning with just the move of the mouse.

However, later that day, the same freezing issues and no boot, no chime symptoms began emerging, and after it refused to chime from restart any more, I DIY reflowed it again.

Once again, the same thing. Worked fine for hours, but again the symptoms returned.

So, I believe that, for this specific problem with these symptoms, it is the Intel SLA5U Northbridge chip which is to blame, and is probably due to the thermal expansion/contraction over time causing the BGA solder balls to not form a proper conn ection to the logic board. I am going to attempt a Re-Balling of the northbridge chip next time, to see if this will well and truly "permanently" fix this problem, and get the iMac back to life. ^_^

I found this YouTube video and note from a group who had similar symptoms with a White Intel iMac, and they found that a reflow was the answer.

http://www.youtube.com/watch?v=ZSYNiKLvvAk

---------

Could other people who are experiencing this problem, please give the reflow a go and report back on your success?, it would be great if we could narrow this issue down and get to say - "this problem is caused by the Northbridge chip, Re-ball to fix", etc..

^_^

Thanks everyone.
- Sylph

[easez]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Thanks for the info. This is a very interesting thread. I've been reading up on this thread.

I currently have an white iMac with a similar issues. I disassembled the iMac and I noticed that 1 led is lit up on the motherboard but the system doesn't power on at all when I hit the power button. If anyone has any pointers please feel free to respond.

[Toasty]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

@ easez: Is yours the Intel unit or the G5 series? This thread is specifically about the latter.

See the other 60 threads or so regarding the older 17" or 20" units or start a new thread of your own so as to not confuse anyone.

Toast

[easez]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Ok sorry for the confusion. Its a Intel unit.

[sylphhawkins]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

@ easez
Personally I don't have any experience working on the intel iMac's that were still in white cases (only the G5 iMacs and then the Aluminium+glass intel iMacs), but have you had a look at the you tube link I posted above, showing a repair shop talking about a White iMac Intel CoreDuo?, I can't remember if they stated what the LED status was on the logic board before they did the reflow and repair?, maybe they also only had 1 LED lit? (usually, on the iMac's, 1 LED lit on the motherboard indicates that the logic board is getting trickle power from the PSU, however, LED 2 should light up when the power button is pressed, indicating correct 3.3v, 5v and 12v supply to the logic board.)

Usually, if LED 2 won't come on, you go straight to checking the Capacitors firstly on both the logic board and the PSU (In the past, I have had these same symptoms on iMac G5's, and they have mostly been due to PSU problems, not the logic board, maybe you can test with another PSU?, or open it up and check for any signs of faulty caps?)

Lastly, I found this article on iFixit, hopefully referring to your model of intel iMac CoreDuo, and some of their repair notes and investigations:

http://www.ifixit.com/Answers/View/35617/iMac+won't+start,+diagnostic+LED's+checked,+what+it+mean

Good luck!. ^_^

[easez]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

@ sylphhawkins
Thanks for the reply. Yes I'll check into that youtube link. The mac store quoted me 600 for this repair and the motherboard was shot. The machine itself isn't worth this amount. the led on the left is solid. I do hear (sound) chimes every 30secs or so. I don't have another PSU to test right now.

[strebor71]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Hoho!

To everyone who is watching this thread about the iMac 7,1 repair.

I seem to have been able to isolate my problems (and the repair ^_^ ) down to the Northbridge chip. On this model (a mid-2007 iMac 7,1) the northbridge chip is an Intel SLA5U.

Removing the heatsink and performing a quick DIY reflow of the chip (I used an old tea-light candle tin cup filled with methyl spirits, and set it alight with the imac powered on, to heat up the northbridge chip enough to reflow the solder BGA balls underneath).

*******
P.S. - This idea comes from the "DIY reflow iBook G4 GPU" idea, and I'm aware of the risky implications of heating the northbridge chip itself to reflow the solder, so please do not reply with negative comments about the technique. ^_^
*******

Once the methyl spirits had finished burning (been used up), I turned off the imac and allowed it to cool for an hour.

Powering it back on, and the iMac booted and chimed fine!, ran flawlessly for hours. Booted into OSX 10.6, then bootcamped and installed XP, ran windows fine.
I left it running for over 12 hours over night, and it jumped straight back to action the next morning with just the move of the mouse.

However, later that day, the same freezing issues and no boot, no chime symptoms began emerging, and after it refused to chime from restart any more, I DIY reflowed it again.

Once again, the same thing. Worked fine for hours, but again the symptoms returned.

So, I believe that, for this specific problem with these symptoms, it is the Intel SLA5U Northbridge chip which is to blame, and is probably due to the thermal expansion/contraction over time causing the BGA solder balls to not form a proper conn ection to the logic board. I am going to attempt a Re-Balling of the northbridge chip next time, to see if this will well and truly "permanently" fix this problem, and get the iMac back to life. ^_^

I found this YouTube video and note from a group who had similar symptoms with a White Intel iMac, and they found that a reflow was the answer.

http://www.youtube.com/watch?v=ZSYNiKLvvAk

---------

Could other people who are experiencing this problem, please give the reflow a go and report back on your success?, it would be great if we could narrow this issue down and get to say - "this problem is caused by the Northbridge chip, Re-ball to fix", etc..

^_^

Thanks everyone.
- Sylph

I have the same iMac 7,1 Black screen, No post, No Chime BS. As a last resort attempted to re-flow my logic board. I have successfully repaired my Xbox 360 that had the dreaded 3 ring of death problem with a oven re-flow technique. This method basically involves removing the logic board from the computer, cleaning all the thermal compound from the chips, and insulate all but a few spots on the board to be exposed. I took several different dish towel sized pieces of fabric, folded them into several layers and taped them into place with some packing tape. with all but a small area over the two main chips on the logic board, one on each side in my case, i then wrapped the whole thing in a layer or two of aluminum foil, again only exposing the two small areas on the board (approx. 2-3 inches square). I then preheated my full sized oven to about 350 degrees and placed the board on a cookie rack placed on a baking pan so that there was good air flow around the underside of the board into the oven and turned the temp up to 450 degrees. as soon as the temp got over around 420-430 i left it in the oven for about 3 mins., then turned off the oven, opened the door partially and let it cool down in the oven. After putting the whole thing back together I crossed my fingers and hit the power button. Whalla!! success! the computer actually posted, chimed and booted into lion like nothing had ever happened. I rebooted the computer a few times then turned it off so that i could finish putting the frame and glass onto the computer. I got it all put back together and hit the power button and . . . . . . Nothing, right back to black screen, no post no chime. I guess i will have to try it again because it obviously is the only solution to the problem. I would really rather not have to tear this whole thing down again to do so. I might give the tea cup method a shot. Could you please explain in more detail exactly what the process is? should i turn the power to the unit on? how much alcohol to i put in the tea cup? can i use rubbing alcohol? how long do i let the fire burn for? any other suggestions greatly appreciated.

[antechinus55]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Sylph
did you ever get your imac working again? I have similar problems, but, following reading this thread, I checked the video card (hd 2400 xt 128mb) on my alum 20" imac and it is DEEFINITELY very very dead. So I need a new video card and I was wondering where you got your one from?

[sylphhawkins]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Hi guys, sorry for the long wait for my reply, I have been buys and hadn't checked this post for a while. ^_^

To answer your question about the tea-light re-flow method, it is done with the iMac turned on (the help heat up the chip internally as well as externally), and I found that a single full tea-light "cup" of alcohol burned for about 20 or 30 mins?, and was enough to get the iMac to POST and boot fine again, however it never stuck for longer than a few days at best.

This leads me to think that a more permanent solution would have to be a complete chip Re-BALL, and while I was attempting this my self, I accidentally ripped traces off the board from under the Northbridge chip because I had not pre-heated the board from underneath correctly first, =p, *woops*

Personally I would find a RE-BALLING business and explain what you want done, then send it in and see if it fixes the problem completely.

I hope that it does, and we can all finally lay this confusing issue to rest, and at least have a major solution for more longer-term repairs of these great iMacs.


----

Also, RE: the GPU video card being very very dead, =p

Can I just ask what steps you took to verify this?, as I did find that at one stage in the testing process, I thought my GPU was dead because I could remote login via SSL and use the iMac fine, however I paid out for a new GPU, and it still didn't solve the problems, as I mention in the earlier posts.

If you're sure this is your problem though, I simply found a used card on eBay from a user who was scrapping his iMac after the screen was destroyed.

I think that I ended up paying $150 AU for it or there abouts (can't quite remember now), and the card definitely works fine, as it's now in my new old iMac 20" 7,1 that I picked up.

I would also look for the lower-spec'd 128mb 2400xt, as it will be cheaper than the 256mb card for sure. ^_^

- Hope this helps guys, and please PLEASE keep posting on this thread about your progress, as the more solutions/repairs/comments/findings that we can gather, the better we can all help others with this in the future. =)

-Sylph

[Th3_uN1Qu3]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Talking about reflow methods: The oven is a much better solution than the torch or hot air station. If you hit the same spot for too long with the hot air, the board is damaged irreversibly. Whereas with the oven the heat is even and the solder reflows on the entire board. A DMM with temperature probe can be had for $10 and that's all you need.

I've seen reballs last less than reflows so IMO, reballing isn't recommended if you have a board with a known high failure rate. More important isn't the reflow/reball operation itself, but what you do afterwards, as it is inevitably going to fail again soon if you leave it as it was. Make sure the affected chip has good thermal compound applied and the heatsink screwed on really tight. If it has standoffs instead of screws replace them with screws. Also don't let the board bend underneath the chip - put something in the case under that spot to support the board.

After you're done, stress test the board and watch the temperatures reported by the chip - it should take several minutes for it to heat up to maximum temperature, and just a bit less to cool back down when the test is stopped. If the temperature changes are sudden then the heatsink isn't making good contact.

[JVarney]

Re: Aluminium intel iMac (2007 model), wont POST, no chime, bad PSU?

Hi everyone. I have found this thread quite interesting as I have a similar problem. I have a 2008 20" iMac Intel which was struck by lightening. I have gone through the post to see what could be checked. I have checked point 5 on the psu and get 5.3! From what I have read this is not normal. None of the LEDs are on and nothing else seems to be 'alive'. I would like to bypass the standard psu and use an external source just for testing but I am not sure what the 10 connections are for. Could someone point me in the right direction? I have searched the Internet for a pinout for the psu but can't seem to find one for this model (614-0420). Thanks.

Jason.