Please help trooubleshooting 27" iMac power supply - Page 1
Forum section: electronics / repair

author: Frankentronics
author_rank: Regular Contributor
timestamp: November 19, 2017, 06:30:48 pm
content: Greetings,This is my first post and I'm sorry it has to be a cry for help. My wife's 27" iMac (model 12,2) just died on her, while in use (just went dead). Now it doesn't do anything when we try to power up.This is what I've done so far (I only have a basic knowledge of electronics).I opened the iMac and got to the power supply. There is continuity between the exterior power chord terminals and the internal connections to the 2 pins on the power board. I tested the continuity, got beeps and the voltmeter also reads 120V AC.I removed the power supply board and first drained the big caps with a big resistor. The caps do not look swollen. Nothing on that board looks burned.I reinstalled and still nothing, so I want to continue troubleshooting.Questions...1 - I do not have an ESR meter, but I do have one of those small electronic component testers. If I connect test leads to that tester, can I test the ESR of the caps while in circuit?2 - Also, I heard that you should not really take a switching power supply and connect it to AC main, unless the outputs are also connected to something. But I see YouTube videos of folks doing just that, to test the DC outputs of such power supplies. So, is it safe to disconnect the output of that power supply and test the DC? If so, how do I really know it's outputting the proper DC voltages?3 - I have another identical computer. Is it safe to remove the power supply from that iMac and put it into my wife's iMac, to see if it works?4 - Any other ideas what I might do or what other parts of the computer might be at fault?Many thanks...

author: wraper
author_rank: Unknown
timestamp: November 19, 2017, 06:49:11 pm
content: First check if fuse(s) isn't not blown. Be wary that primary side capacitors may still be charged with high voltage.QuoteSafe, if your hands are straight.

author: Armadillo
author_rank: Super Contributor
timestamp: November 19, 2017, 07:54:45 pm
content: Quote from: Adinol on November 19, 2017, 06:30:48 pmReplacing the identical power supply module would be the easiest first step. Top DC connector and bottom AC connector. Its all begins with generating the DC 12V.And then listen for fans noise and other activities..Hope that it works for you.

author: cdev
author_rank: Super Contributor
timestamp: November 19, 2017, 08:07:02 pm
content: Whoa..If its completely dead it may be something quite simple, before you start doing things, since you have another computer, you should try to find the Apple repair docs on that particular model, If you are certain you both have the same machine, look in your "about this Macintosh" The model name should be there."about this Macintosh" Find it online by other facts you know about it, its year of manufacture, etc.Try the repair manuals resources listed here in the wiki.Its likely this happens to other people too. Don't panic, calm down, dont do anything. Think slowly and clearly..No power at all? No nothing when you try to turn it on?I would NOT at this stage put your other power supply in this machine. If your wife absolutely needs to work right nowI would put her hard drive in your working machine so she can continue what she was doing and then when it comes up check the logs..There may be some indication in logs of some problem right before it died. But probably not.Its a long shot. If you dont know what youre doing dont do anything with the power supply just yet.You should find and get the Apple documentation for that model. Then come back here.You are likely to find better info there than anything people here tell you unless they have experience working with that machine.It is likely something failed thats easy to fix but the chance of you breaking something is high if you simply start poking around, I would not do it.If she needs to work, give her your machine for now swap out the hard drives or put her HD into an external case or attach it to a USB SATA adaptor and power supply.. then boot it from her drive.. that will turn your machine into hers.

author: kripton2035
author_rank: Super Contributor
timestamp: November 19, 2017, 09:22:23 pm
content: it can mostly be the power supply that is dead, or also the graphic card, famous to die on these models (more often than the power supply)(temporary) solution is to heat the graphic chip with a hot air around 200°C for 3 mins and see what happens. this can work for several months, and you have to do it again later.not trivial if you've never done this before.ps: your iMac 2011 is not yet obsolete (but will be soon be in some months from now) you can take it to an apple service center, they will change what is wrong. if it is the graphic card, you can even cry by apple online, and may be get a refund as it is a well known problem.

author: Armadillo
author_rank: Super Contributor
timestamp: November 19, 2017, 10:01:35 pm
content: Yeah, completely dead and silence, most likely is the primary greenchip, mosfet and fuse, otherwise there should be some other activities happening.Of course, the proper way is to bring it to apple service center. Yes, you should in fact bring it there than forum discussion.But the worse is to be talked into a labyrinth of nowhere and then ended up in a directional talker repair shop, sure cost you a bomb.I am sure you are wiser. cheers.

author: Frankentronics
author_rank: Regular Contributor
timestamp: November 20, 2017, 01:19:54 am
content: Wow! Got so many replies so quickly. Thank you all so much.Yes, I was already getting ready to put my wife's HD into an enclosure and boot it from my iMac.Taking the iMac to the shop is my last resort. I'm trying to determine if it's something I can fix and pay for the parts, only. If I can positively determine it's the power supply it would be a waste to pay for labor, as I can just replace it myself. I just want to make sure it is in fact the power supply, before buying a replacement.Also, if there was a way to positively determine that it was a bad cap I could obviously change the cap. But I have a feeling it is not a bad cap.Quote from: cdev on November 19, 2017, 08:07:02 pmThat was exactly my thinking.Quote from: cdev on November 19, 2017, 08:07:02 pmI do have the exact same machine but can't find Apple repair docs in "about this Mac". I also looked a bit online (even before I posted here) but not found the resource, as of yet. I'll look some more.In the "about this Mac" it says it is an iMac12,2 but when I look online I find different model names, such as "iMac 27" Intel EMC 2639", and so on. I just need to look some more.Quote from: cdev on November 19, 2017, 08:07:02 pmI didn't know there was a wiki here... I'll look.Quote from: cdev on November 19, 2017, 08:07:02 pmThat's why I asked. For future reference, is is possible there is something else wrong, which killed the power supply, and I risk killing another power supply with such test?Quote from: Armadillo on November 19, 2017, 10:01:35 pmI was also thinking that if it was just faulty caps I'd still be seeing/hearing some activity.After I reassembled the Mac I also though it could be a fuse, but I don't remember seeing a fuse on that board. I'll take it apart again and look for one.Again, I cannot thank you enough, all of you, for replying so quickly.There is still one question I would like to know the answer to (also just for general knowledge). Can one just connect any switching power supply to the mains voltage if there are no loads on the outputs?Thanks...

author: cdev
author_rank: Super Contributor
timestamp: November 20, 2017, 01:32:00 am
content: Dont start trying to reflow your board. You will learn a very expensive lesson.Same thing, I hate to say this but DONT bring it to an Apple Service Station. They wont fix it and they will quote you a price which is so nuts they basically are trying to sell you a new one. Even if its a simple repair, under many conditions, they wont even try to fix it. You wont get it in and out of there for less than a few hundred dollars. As likely as not, you will never see it again.Your safest bet is to GET THE DOCUMENTATION for that model.. Everybody thinks they know what to do Its the same thing that happened to theirs, but the fact is, hundreds of things might have gone wrong.get the repair manual and then follow the procedures in it exactly to figure out what went wrong. If you need some piece of equipment you dont have to figure that out, BUY IT, basic tools like a nice small DMM are cheap. Black Friday awaits..I cant tell you how many times Ive thought it was one thing and it was something else. The power supply turned itself off because ---YOU DONT KNOW..maybe its really simple, maybe it isn't but nomatter what it is its almost certain to require a part and or tool you dont have in your junkbox. Macintoshes are like that.You would be wise to take it slowly bit by bit. #1 lesson,investigate before DOING anything.Do something only when you are absolutely sure thats what needs to be done, not by trial and error..Or you will kill your 'patient' - His and her matching 27 inch imacs.. need I be any more explicit, this Imac, being your wife's is not something you want to experiment on.. and kill..Please, trust me, you need to treat it as if its your wife there and not her computer. Don't break it.Don't mess around with the power supply until you have the repair doc, or you will just as likely as not make the problem worse. The reason it turned itself off is likely because something failed and it did that to save itself.the Apple model number is usually a long number and its on the box.. I dont have any Imacs.You need to do more Googling. Its not 12,2 Its a long number but not your serial number, we don't want to know thatIs it one of these?https://everymac.com/ultimate-mac-lookup/?search_keywords=iMac12,2Maybe this one?https://everymac.com/systems/apple/imac/specs/imac-core-i5-2.7-27-inch-aluminum-mid-2011-thunderbolt-specs.html

author: Frankentronics
author_rank: Regular Contributor
timestamp: November 20, 2017, 03:02:23 am
content: Thank you, again, cdev.The machine is an iMac "Core i7" 3.4 27-Inch (Mid-2011). I did a lot of Googling and just can't find a repair manual.I do have a decent DMM, BK Precision 2707B, and just in general want to learn more about electronics.However, there is an important update.Just before I was going to open the iMac to remove the HD, I once again pressed the power button. The machine powered up.I do not consider it fixed as I believe something is wrong. Obviously not the fuse. But that iMac has been acting weird at times when powering up. Sometimes, while powering up, the screen gets stuck on the grey stage forever. We normally hold down the power button to force it to shut down and reboot. I'm not sure if it's related and I'm not sure if I can even investigate what the problem is when the computer is working. But I would like to have that repair manual handy, as I think it's just a matter of time before it goes dead again.Any thoughts?Thanks...

author: kripton2035
author_rank: Super Contributor
timestamp: November 20, 2017, 07:06:50 am
content: the iMac 27 has 4 leds, located at the right of the ram slots,with a power cord pluged in, you should see one led on, meaning the trickle power is here, so the power supply is good.the second one lights up when you press the power button, the 4th is when the cpu communicates with the graphic card.this is the test to do when the mac does not power on.you should locate these leds while it works, because they are not obvious, specially when off ...again, I'm pretty sure now that this is a graphic card failure, like almost of these 2011 imacs. get another one while there are available (and claim by apple because it's a known problem, and it will cost you some $500...) you can find them also on ebay for a not so lower price.you could also have been in front of a power supply security state, then you must unplug the cord, press the power button for 10s, then wait 10s and plug it again to reset to normal state. it's sometimes simple as this. ( and you can see it with the 1st led is on)have a good day.

author: Frankentronics
author_rank: Regular Contributor
timestamp: November 20, 2017, 01:57:54 pm
content: Quote from: kripton2035 on November 20, 2017, 07:06:50 amThanks for this information. After some Googling I found these are called diagnostic LEDs and are on the logic board and I need to remove the screen again to see them, correct? I can't see them through the vent holes at the bottom, so the screen needs to be off. I'll do this tonight.Quote from: kripton2035 on November 20, 2017, 07:06:50 amWe plan to keep both iMacs for quite some time so perhaps it would be good to grab one graphics card, even if this problem turns out to be something else, just to have a "spare tire".When I go to "About this Mac > Hardware > Graphics/Displays" it says "Chipset Model: AMD Radeon HD 6970M". This is the part and model number I should be looking for, right?Questions:1 - Is there perhaps another compatible model that is an upgrade and perhaps does not have the same known problem?2 - I see some on eBay, most without a heatsink. Any reason why I should avoid buying one without the heatsink?3 - Lastly, most that are offered for sale will be used and I guess chances are they had the same problem and they just stuck them in the oven to reflow the solder. Is there any way of knowing if the solder has been reflown?Quote from: kripton2035 on November 20, 2017, 07:06:50 amI couldn't find any Google results for "iMac power supply security state" but I can understand what you meant. If or when it happens again I'll try this procedure to rule out.Thanks...

author: kripton2035
author_rank: Super Contributor
timestamp: November 20, 2017, 06:29:18 pm
content: Quote from: Adinol on November 20, 2017, 01:57:54 pmyes ... and no, as it is a model specific to the imac 27", you cannot grab any card with that referenceQuote from: Adinol on November 20, 2017, 01:57:54 pmno, there are no upgrade to these models, although there is a 1Gb and a 2Gb model that fits in these imacs.I have seen a LOT of 1Gb model failure, and no 2Gb models.as the 2Gb models have been sold quite rarely, it's not a good statistic, but you could try to get a 2Gb one ?Quote from: Adinol on November 20, 2017, 01:57:54 pmyou don't need the heatsink as it is already inside your imacs. but it's a little easier to change if it is already mounted.Quote from: Adinol on November 20, 2017, 01:57:54 pmno method I'm aware off to know that . sorry.

author: kripton2035
author_rank: Super Contributor
timestamp: November 20, 2017, 06:42:07 pm
content: you also have a lower model graphic card, with only 512Mb of memory - no problem with them tooref Model euro price excl VAT apple sells the card661-5967 GRAPHICS,AMD RADEON 6770M,512MB 370.79661-5968 GRAPHICS,AMD RADEON 6970M,1GB 638.93661-5969 GRAPHICS,AMD RADEON 6970M,2GB 691.96

author: cdev
author_rank: Super Contributor
timestamp: November 20, 2017, 07:34:48 pm
content: What was in your logs, any indication any HW was failing?There is a program called Apple Hardware Test. You should try to find a copy of it from a few years back. It used to come with Apple Care.How did you decide it was the graphics causing the boot problem? Did you go to all the manuals sites and look under A for Apple? Google isn't going to do that for you. You need to search the deep web yourself.If your graphics card isn't clearly at fault, its dumb to buy another one.

author: Rasz
author_rank: Super Contributor
timestamp: November 20, 2017, 08:32:39 pm
content: Quote from: Adinol on November 20, 2017, 01:57:54 pmYour plans do not align with Apples. Apple plans for you to buy new model every 2-3 years.Purely by coincidence Apple was forced (dragged kicking and screaming) to recall almost every single model of their computers with discrete GPUs ever since ~2007, starting with Nvidia 8600M Macbooks. Even to this day the newest shiniest touchbar Macbooks cook GPU keeping a cosy 80-100'C inside the case.

author: Frankentronics
author_rank: Regular Contributor
timestamp: November 21, 2017, 02:59:04 am
content: OK, I finally had time to look for those logs. There's a lot to scan through, but here is the last thing that was logged on Nov 18, right before the crash. Followed by the boot log of the next day.Code:Nov 18 12:38:31 Partenze webfilterproxyd: isAppleURLString - checking: r5---sn-ab5szn7y.googlevideo.comNov 18 12:38:31 Partenze webfilterproxyd: isAllowedAuthURLString - checking: r5---sn-ab5szn7y.googlevideo.comNov 18 12:38:31 Partenze webfilterproxyd: isAllowedAuthURLString - returning NONov 18 12:38:31 Partenze parentalcontrolsd: contentFilterPageWasVisited:address: enteredNov 18 12:38:32 Partenze firefox: CVCGDisplayLink::setCurrentDisplay didn't find a valid display - falling back to 60HzNov 18 12:38:32 Partenze webfilterproxyd: isAppleURLString - checking: i.ytimg.comNov 18 12:38:32 Partenze webfilterproxyd: isAllowedAuthURLString - checking: i.ytimg.comNov 18 12:38:32 Partenze webfilterproxyd: isAllowedAuthURLString - returning NONov 18 12:38:32 Partenze parentalcontrolsd: contentFilterPageWasVisited:address: enteredNov 18 12:38:32 Partenze webfilterproxyd: isAppleURLString - checking: i.ytimg.comNov 18 12:38:32 Partenze webfilterproxyd: isAllowedAuthURLString - checking: i.ytimg.comNov 18 12:38:32 Partenze webfilterproxyd: isAllowedAuthURLString - returning NONov 18 12:38:32 Partenze parentalcontrolsd: contentFilterPageWasVisited:address: enteredNov 18 12:38:33 Partenze firefox: CVCGDisplayLink::setCurrentDisplay didn't find a valid display - falling back to 60HzNov 18 12:38:34 --- last message repeated 3 times ---Nov 18 12:38:34 Partenze webfilterproxyd: isAppleURLString - checking: r5---sn-ab5szn7y.googlevideo.comNov 18 12:38:34 Partenze webfilterproxyd: isAllowedAuthURLString - checking: r5---sn-ab5szn7y.googlevideo.comNov 18 12:38:34 Partenze webfilterproxyd: isAllowedAuthURLString - returning NONov 18 12:38:34 Partenze parentalcontrolsd: contentFilterPageWasVisited:address: enteredNov 18 12:38:35 Partenze firefox: CVCGDisplayLink::setCurrentDisplay didn't find a valid display - falling back to 60HzNov 18 12:38:39 --- last message repeated 6 times --- Nov 18 12:38:39 Partenze webfilterproxyd: isAppleURLString - checking: i.ytimg.comNov 18 12:38:39 Partenze webfilterproxyd: isAllowedAuthURLString - checking: i.ytimg.comNov 18 12:38:39 Partenze webfilterproxyd: isAllowedAuthURLString - returning NONov 18 12:38:39 Partenze parentalcontrolsd: contentFilterPageWasVisited:address: enteredNov 18 12:38:39 Partenze webfilterproxyd: isAppleURLString - checking: i.ytimg.comNov 18 12:38:39 Partenze webfilterproxyd: isAllowedAuthURLString - checking: i.ytimg.comNov 18 12:38:39 Partenze webfilterproxyd: isAllowedAuthURLString - returning NONov 18 12:38:39 Partenze parentalcontrolsd: contentFilterPageWasVisited:address: enteredNov 18 12:38:39 Partenze firefox: CVCGDisplayLink::setCurrentDisplay didn't find a valid display - falling back to 60HzNov 19 20:54:07 localhost bootlog: BOOT_TIME 1511142847 0There is a recurring message throughout the long log file...CVCGDisplayLink::setCurrentDisplay didn't find a valid display - falling back to 60Hz...what does that mean?And it also happens to be the last message before the crash.So, I'm obviously no expert, so I have to ask... Is there any conclusion that we can reach from this log?Quote from: cdev on November 20, 2017, 07:34:48 pmAfter I saw how much these graphics cards go for I came to the conclusion that for about $300 more I can just buy an entire used iMac, an identical one, and if it works out then keep the current Mac for spare parts. And it sure beats paying Apple service a few hundred dollars to see if they'll be able to fix anything, or to tell me that for a few hundred more they might be able to fix some more.Thanks...

author: cdev
author_rank: Super Contributor
timestamp: November 21, 2017, 03:08:05 am
content: That doesnt look like it would be a problem. You are running Aqua, not X. On X you might get messages like that if you had never bothered to set up an xorg.conf, then it just uses the defaults for a one screen setup. the main screen is the main screen. Does your imac have an external monitor jack? Likely a mini HDMI or a mini DVI or a mini display port. Macs work very well with multiple monitors.But as far as your problem, I dont think the messages you posted have anything to do with it. What about other logs? There are lots of logs..

author: Frankentronics
author_rank: Regular Contributor
timestamp: November 21, 2017, 03:28:05 am
content: Quote from: kripton2035 on November 20, 2017, 07:06:50 amOK, now I just completed the test with the screen removed, observing the diagnostic LEDs.The 1st LED turned on when I plugged the power chord.The 2nd LED turned on at the moment I pressed the power button.The 3rd LED turned on when I heard the booting sound, then half a minute later the fans started spinningThe 4th LED did not light up after a few minutes, so I held the power button for a few seconds, the computer shut off and the only LED left on is the 1st one.What conclusion can we draw from this test?Thanks...

author: cdev
author_rank: Super Contributor
timestamp: November 21, 2017, 03:30:30 am
content: You need to know what the Apple docs say for your unit!Also, look at Louis Rossmann's videos - maybe search on "iMac"?Did you reset the PRAM?(you know, basic Mac stuff)

author: kripton2035
author_rank: Super Contributor
timestamp: November 21, 2017, 07:29:03 am
content: Quote from: cdev on November 21, 2017, 03:30:30 amLouis did a lot of laptops macbookpro's, but quite no iMacs (I've not found any ?) , and no iMacs graphics cards

author: kripton2035
author_rank: Super Contributor
timestamp: November 21, 2017, 07:31:10 am
content: Quote from: Adinol on November 21, 2017, 03:28:05 amthat your CPU has difficulties to communicate with the graphic card, so again, the graphic card must be dying.it's 99% of the faults on these models. power supplies gets bad quite only with overvoltage on mains.

author: Frankentronics
author_rank: Regular Contributor
timestamp: November 21, 2017, 01:58:33 pm
content: Quote from: cdev on November 21, 2017, 03:08:05 amLooking at the logs is something new to me and I am doing a lot of Googling to get info on how to do this (I want to be respectful of everyone's time and don't want to bother anyone here to spoon feed me, step-by-step).But just so that I clearly understand what you mean... When you ask about the other logs, are you referring to other logs in that same log file, or other logs that are stored in other files?I copied the above logs from a file "var/log/system.log". Every day the Mac stores a fresh "system.log" file in that directory. I used Console to access that and I can see there are dozens of other log files and directories that I can access. Some are clearly specific to some applications and some are labeled with names that are impossible to interpret without Googling.Also, there are so many log files and so many lines in each file that I don't want to clutter this forum by copying hundreds of lines of log code. I'm new here and don't know the forum etiquette. Is it OK to copy and paste a long log that is several pages long?Further, if it would help to look at some specific log file, other than "system.log", I would be glad to post it. But which file?Lastly, after I did the diagnostic LED test I put the screen back on and my wife rebooted the computer. That time, as it often happens, the system got stuck on a grey screen and I had to hold down the power button to make it advance. I assume that if I had a clear view of the LEDs (which, for some mind boggling reason, Apple decided to hide behind the screen) I would see that the 4th LED did not light up. Of course, the computer also added lines to the "system.log" file. In fact, it did the same thing when I booted with the screen removed. I looked at those logs and discovered hundreds of lines of code that I cannot make much sense of.So, my question is this... Should I copy and paste all that (hundreds of lines) of log code here? Will it help? Or would I just be blasting this forum with too much information and too much expectation from this community. Again, I am new here and don't know the etiquette.Please let me know.Thanks...PS - About the power supply...Quote from: kripton2035 on November 21, 2017, 07:31:10 amThat computer is plugged into a heavy duty line conditioner, so there should be no spikes or line noise hitting the Mac's power supply. The only other units plugged into that same line conditioner are 2 external hard drives.

author: Bashstreet
author_rank: Frequent Contributor
timestamp: November 21, 2017, 03:26:58 pm
content: Repairing mac's...

author: kripton2035
author_rank: Super Contributor
timestamp: November 21, 2017, 05:26:54 pm
content: Quote from: Bashstreet on November 21, 2017, 03:26:58 pmis easier than you think ...

author: cdev
author_rank: Super Contributor
timestamp: November 22, 2017, 12:26:54 am
content: If I were you I would let the logs be for now and concentrate on finding a service manual for your imac on one of the repair manual sites.If your machine is having problems booting its either a hardware or software problem. You need better help than any of us likely can give you because we don own imacs.You can learn a lot from the Apple program "Console" if its a software issue causing the hang on boot. Did you reset your PRAM? There is a multi fingered key sequence you must press while also restarting it, do that until it has made a "bong" sound and restarted three timesYou should also hold down the key when you just boot it regularly to get a more verbose boot.find the service docs for your Mac.You can and should add additional logs you find to console.The logs it can show you are shown in a tree, system.log is an important logs for the whole machine. There are other logs too. To be honest with you my Mac laptop, like me, are so old we basically are still living in the past.So, just go looking for the new log whatever they are now.Look at the directories I mention below. There are likely others too.I can't tell you about newer logs that they may have added since my machine no longer gets software updates and basically is only used when I am in the mood to use a laptop that is really really slow and old..>"Log Database Queries">>All Messages>>Console Messagesthey are under your root Library directory or your username's (which is abbreviated by using the tilde symbol "~" )>>> /Library/Logs>>>> Atyour.service>>>> Boring.service>>>> PlannedObsolescence.service>>> /var/log(Traditional Unix apps logs go here)>>> ~/Library/Logs>>>> Blabla.log>>>> MoreBlabla.log>>>>Gargle>>>> > Blablablablablablabla.log>>>>Mobla>>>>>lalala.app.logQuote from: Adinol on November 21, 2017, 01:58:33 pm

author: Frankentronics
author_rank: Regular Contributor
timestamp: November 22, 2017, 03:00:25 am
content: Quote from: cdev on November 22, 2017, 12:26:54 amYou're not alone. I still sometimes boot my old Mac PowerBook G4 laptop, as it has some applications that never got updated and are the only applications that can open certain files that I occasionally have to open.To answer your question, yes I do periodically reset PRAM. I'll do it again now.I'll look more for the service docs and I'll save the old logs.For now the computer is working, although it is not fixed. But it takes some pressure off as we have time to think.Again, thank you all for taking the time to help me out.

author: cdev
author_rank: Super Contributor
timestamp: November 22, 2017, 03:18:21 am
content: Computers are binary so, you'remuchbetter off with a 1 than a 0Dust or vacuum out the inside (in a non static producing way) so it can stay cool..

author: cdev
author_rank: Super Contributor
timestamp: November 22, 2017, 03:22:24 am
content: Do you have children? If not you should turn off the parental protection.

author: kripton2035
author_rank: Super Contributor
timestamp: November 22, 2017, 07:10:56 am
content: you won't find a lot of informations in the 27" service manual except the leds meaning I gave you earlier.these service manuals, I quite never use them. you have 5 boards in the computer, it's all simple logic to find the faulty one.in your case, it's certainly the graphic card faulty.there was an exchange program for these, but it is discontinued now.we have an internal program for the apple technicians, that tells us if the graphic card is considered as defective from this exchange program.go to an apple service center, ask them ho much they charge you for launching this program on your imacif the program says "failed" then you can claim apple to change it free of charge.these 2011 imacs will become vintage in the coming months (may be even in december), so don't loose time.after that it will be impossible to change them, you will get only loosy cards from ebay, or heat the graphic chip for some months of use.

author: kripton2035
author_rank: Super Contributor
timestamp: November 22, 2017, 07:16:01 am
content: Quote from: Adinol on November 22, 2017, 03:00:25 amyou can use a free program called "sheepshaver" that will let you have a mac os 9 virtual machine in your actuel macplus if you have an ssd drive, it will be blazing fast compared to these olg powerbooks.

author: a.ekholm
author_rank: Contributor
timestamp: November 22, 2017, 05:41:01 pm
content: I had a imac 27" which I did a reflow with a heatgun on the gpu. Worked fine. I did use a software that increased the fanspeed after wardsSkickat från min SM-G920F via Tapatalk

author: kripton2035
author_rank: Super Contributor
timestamp: November 22, 2017, 06:16:37 pm
content: how long ago did you heat your graphic card ?

author: a.ekholm
author_rank: Contributor
timestamp: November 22, 2017, 06:39:38 pm
content: Don't remember followed a guide on YouTube. Had a ir-thermometer to monitor temp. But think it was 2minutesSkickat från min SM-G920F via Tapatalk

author: kripton2035
author_rank: Super Contributor
timestamp: November 22, 2017, 07:09:07 pm
content: not how much time you heated the card, but when did you do it ? 6 months ago, more ?

author: a.ekholm
author_rank: Contributor
timestamp: November 22, 2017, 07:53:51 pm
content: Sorry!I had it a couple of months (bought it broken) and did some stress tests. And with software the temp was lowered allot. Then I sold it and bought a rigol 1054z oscilloscope for the money. So without the imac I shouldn't be hereSkickat från min SM-G920F via Tapatalk