iMac mid 2011 27" SMC issue?

[alpina]

Hi I'm new to this forum and Mac's in particular, dare I say am a PC guy, I was asked to have a look at his mid 2011 iMac that was having issues, he was having problems with it starting from the power button then eventually it wouldn't start at all even with every reset known, when I opened it up I discovered there was water damage (corrosion) to the logic board especially around the smc chip.
I cleaned the best I could but with still no joy, but I discovered that if I remove the Pram battery ( I call it the cmos battery) and reinstall it and plug the iMac into the main power the machine boots to its desktop and runs without any issues without touching the power button at the rear.
I have taken some pictures from an area on the board that looks suspect to me and I've replaced the power supply with a new one so that's ruled this out, the power button also checks out with the multimeter so no issues there, can someone explain why this wont turn on from the power button
any you guys shed some light on the issue
Thanks in advance

Sorry the board is a 820-2828-a 27" mid 2011
Ed

 

[pigoo3]

...I was asked to have a look at his mid 2011 iMac that was having issues, he was having problems with it starting from the power button then eventually it wouldn't start at all even with every reset known, when I opened it up I discovered there was water damage (corrosion) to the logic board especially around the smc chip.
I cleaned the best I could but with still no joy, but I discovered that if I remove the Pram battery ( I call it the cmos battery) and reinstall it and plug the iMac into the main power the machine boots to its desktop and runs without any issues without touching the power button at the rear.

Are you sure we are dealing with water damage? I can't tell you the last time I heard someone have a water damaged Apple desktop here on Mac-Forums. I'm not saying it's not possible…just very unusual to hear someone with a water damaged desktop.

When you say that the iMac will start up if the PRAM/CMOS battery is removed, replaced, and the computer plugged in…are you staying that it starts up all by itself once plugged in (no pressing of the power button)?

- Nick

 

[alpina]

Thanks Nick for your reply
Yes I know it sounds quite difficult to get an iMac water damaged , but this one was in a extremely damp bedroom, its not a spillage problem it was more moisture in the room that caused the corrosion on the logic board the Ram slot is missing so that was the area that the moisture was entering

The area on the board that was mostly corroded was on and around the SMC chip and the Ram slots but this might not be the problem as this has now cleaned up well, the area that I took the images may be the issue and has always been the issue, but my knowledge of surface mounted components is very limited the area just doesn't look right the two components have a bridge of solder between them.

When I remove the battery and replace again then plug the power cable in the back, it starts up by its self without pressing the power button, I thought maybe this was me resetting the system and bypassing the SMC chip.

Could the Area on the logic board in the images be the cause of the problem, I didn't think an overheating LCD would cause this sort of Temperature to melt solder, if someone could confirm this is how the board should look then it looks like a new logic board is required

I hope this makes sense

 

[pigoo3]

When I remove the battery and replace again then plug the power cable in the back, it starts up by its self without pressing the power button, I thought maybe this was me resetting the system and bypassing the SMC chip.

The computer definitely shouldn't startup on its own after being plugged in. Maybe the power button is stuck in the depressed/pushed position, or maybe the contacts in the power button have bridged in some way (melted solder)

Could the Area on the logic board in the images be the cause of the problem, I didn't think an overheating LCD would cause this sort of Temperature to melt solder, if someone could confirm this is how the board should look…

I don't think that the LCD can get that hot. If it was heat related…it would be the CPU or GPU generating that much heat (or a faulty fan).

As far as should it look that way. Try going to ifixit.com. Lots of repair procedures there…with lots of photos (by computer model). Hopefully some of the photos will show the area you're interested in…with enough detail.

...then it looks like a new logic board is required
...

If it needs a new logic board…it will be a borderline call on doing it. Most of the time with Apple computers it's not financially worth replacing the logic board. Just too expensive. A replacement logic board may cost you $500+ Current value on a 100% working mid-2011 27" iMac is around $1000.

You may be able to get $400-$500 for this iMac on eBay (in it's current condition). Add to that the $500+ for a replacement logic board…and you're back to $1000 or more. So it's almost better to sell what you got (the owner of the computer)…and buy another 100% used working unit.

Of course if the computer can be repaired without needing a replacement logic board…that's the way to go.

- Nick

 

[alpina]

The computer definitely shouldn't startup on its own after being plugged in. Maybe the power button is stuck in the depressed/pushed position, or maybe the contacts in the power button have bridged in some way (melted solder)

Only if you remove the Cmos Battery , any other time it will only light up number 1 LED and not start, I've carried out a continuity test on the Button and I only get a reading when the button is depressed so its working normally all the way to the connector on the logic board

its so frustrating that the machine works perfect when you get it to the desktop but once you shutdown the machine it will not start back up until you take the display off and remove the Battery, you can put it to sleep and it starts fine as long as you don't disconnect the power supply

Thanks for your Help Nick

 

[pigoo3]

If this computer really is suffering from water damage…I'm sure you must know…water damage can be so hard to diagnose. Could be one thing or multiple things…or something that's working today, may not work tomorrow.

Since this computer seems to work fine after removing & replacing the PRAM battery…and will even work fine if the computer is put to sleep & woken up. It would seem that the chances that it's water damaged would seem minimal.

Since we're talking how this computer was used/stored in damp conditions…this may not be the exact same as suddenly the computer exposed to liquid (like a liquid spill that happens to laptops). It would seem that once the computer was stored in a less moist environment (allowed to dry out)…it could perform normally.

Two things you mentioned in the beginning of this thread were:

- This is not your computer. Since this is not your computer…it is possible that you're not REALLY getting the whole history or accurate history of the computer. Such as preexisting conditions.

- You mentioned replacing the power supply. I'm assuming that you replaced the power supply before discovering the "trick" of removing & reinstalling the PRAM battery…which gets the computer to operate. If so…I'm wondering if the original power supply was reinstalled…if the same thing would happen with the battery.

If I was a betting person. I would bet that the problems with this computer are not moisture or liquid related…but something that was a preexisting condition. Such as this computer worked fine…then something went wrong with it…then it sat in this extremely damp bedroom unused for a long time….which resulted in corrosion.

If this were the case…then the moisture may not be the main issue…but something else. If this solder thing is the real issue…maybe something overheated in the past (CPU, GPU, bad fan, cooling efficiency reduced by dirt/fuzz inside, etc.). Then this over-heating caused a problem. then it sat unused for a long time (or maybe a short time)…leading to the corrosion.

But usually...if a Mac computer overheats…it shuts down before damage occurs. So even this theory isn't perfect.

Or maybe it's not moisture or the solder…but something else that's wrong (and the owner is either not saying or doesn't remember).

- Nick

 

[alpina]

Two things you mentioned in the beginning of this thread were:

- This is not your computer. Since this is not your computer…it is possible that you're not REALLY getting the whole history or accurate history of the computer. Such as preexisting conditions.

- You mentioned replacing the power supply. I'm assuming that you replaced the power supply before discovering the "trick" of removing & reinstalling the PRAM battery…which gets the computer to operate. If so…I'm wondering if the original power supply was reinstalled…if the same thing would happen with the battery.

Your spot on with this it dose the same thing with the old power supply, but I replaced it just as a matter of course to discount a PSU issue , as you know the only thing that it can be is a faulty mobo, You never get the full history of Machines, why people are vague I don't know, you try and get as much info from them as you can

What I've found is that somewhere on the board, its not sending the signal to start when the Power button is pressed, this I thought was when the SMC came into effect, the strange looking area that's in the image is not to far away from the SMC chip and all its surface mounted components,
As you said this could have been a underlying problem from way back and is finally put a nail in the coffin (so to speak) of this area of the Logic board that controls the power on

 

[pigoo3]

Your spot on with this it dose the same thing with the old power supply, but I replaced it just as a matter of course to discount a PSU issue…

Yeah…I was mentioning this as just a point of discussion. Replacing the power supply was a very good idea (I probably would have done the same). And since the computer "works" with both power supply's (when doing the battery trick)…just means the actual problem has not been identified (or at least isn't the power supply).

...as you know the only thing that it can be is a faulty mono…

Exactly (or probably). There just aren't that many parts in there (not much in the way of separate socketed chips or daughter cards). And the "problem" with Mac's is. Usually (most of the time)…the cost of replacing the logic board/motherboard is too expensive. Unlike Windows computers (desktops)…where replacement parts for older computers is usually something that can be gotten at fairly low cost/reasonable prices. Making almost any repair "affordable".

You never get the full history of Machines, why people are vague I don't know, you try and get as much info from them as you can…

I think that sometimes folks are trying to hide something (if they know what is wrong…or they know they did something wrong). Or they are just clueless or forget. Kind of like folks who drive their cars day after day after day…and only know how to put gas in it. If anything goes wrong…they are lost!

For what it's worth (regarding the theory that the solder melted). A good number of Mac computers have issues with the video cards/video hardware (MacBooks, MacBook Pro's, iMac's).

In a lot of cases…the culprit seems to be the "environmentally friendly" solder Apple uses (lead-free)…which has a lower melting point. I don't know of the manufacturers of Windows computers use the same lead-free solder (they probably do). I get the picture that the failure rate isn't quite as high in "Windows boxes".

So maybe with Apple computers…maybe they run hotter internal temps…or the cooling systems are much more sensitive to blockages (dirt, fuzz, or simple external blockages of airflow). Then the lower melting point solder melts/runs…causing problems. I know quite a number of folks have solved this problem by doing the "oven-bake" to reflow the solder.

So with this specific iMac. If the problem is solder related. I'm wondering if it overheated at some point (failure of something in the cooling system) or if the cooling air into the computer or hot air exiting the computer was blocked (causing overheating). This is where I thought maybe we could be dealing with a pre-existing condition.

- Nick

 

[alpina]

Yeah it's the same problem with the lead free solder on all PC related boards , I've had to send many a notebook system board away to have the GPU reballed due to the low melt lead free solder , but this was mainly in notebooks due to the lack of adequate ventilation and older technology that ran at higher temps, PC desktops unlike the iMac have plenty of air circulation and more options to increase cooling so they don't suffer as badly with overheating, but you have to say the iMac does look the part where the PC hasn't changed in an age.

I think this iMac is for the breakers yard sell it as spares if it was a PC it could be sorted for less than $150 it's a shame really nice and quick when you get it running

Thanks for your input Nick it's nice to speak to someone who's on the same wavelength

Ed

 

[pigoo3]

You're very welcome Ed!

That iMac you're working on has a very uncommon problem. And if the very damp bedroom is this bad for a computer…wouldn't it also be pretty bad for the human sleeping in that very damp bedroom (rusty lungs)!

- Nick

 

[gsahli]

I must have missed this - did you ever put a new CMOS battery in?
The battery charges a capacitor - the power button discharges it to (near) zero, The procedure you're doing might be thought to mimic this discharge.
Worth a try.

 

[alpina]

You're very welcome Ed!

That iMac you're working on has a very uncommon problem. And if the very damp bedroom is this bad for a computer…wouldn't it also be pretty bad for the human sleeping in that very damp bedroom (rusty lungs)!

- Nick

Yeah I did mention this as well , told him if the iMac works again not to put it in that bedroom oh ........ And him

 

[alpina]

I must have missed this - did you ever put a new CMOS battery in?
The battery charges a capacitor - the power button discharges it to (near) zero, The procedure you're doing might be thought to mimic this discharge.
Worth a try.

Yeah I've replaced the cmos battery as well for a brand new one ,check voltages and both the old one and the new one checked out fine both reading 3v