iMac A1311 extrange behaviour

[fichamba]

Hello colleagues:

I have in my bench an Apple iMac A1311 (21,5¨), which is driving me nuts.
The machine starts when you push the power, the chime sounds, the Apple logo appears, even the progress bar appears, but when the bar is around the 40% , the machine goes black and restarts by itself. And this is a loop.

Things that I've made:

-The screen presented pink vertical bars. I have done a VGA chip reballing. Succeed. No bars. Clean screen at startup. This problem is solved.

-PRAM resetted. Same results.

-RAM checked and sockets cleaned. No beeps. OK.

-Try to start up the machine from another good verified USB SSD disk, with El Capitan inside. Pressing ALT at startup it presented all possible startup volumes, all correct. I have chosen the external one. Nearly same results (this time the screen goes white forever, no restarts, but it does not work nor load system).

-Tried system recovery thru internet, connected via ethernet. The machine connects (you can see the earth globe), but suddenly white screen and restarts.

-Tried to start it up without internal hard disk, and as before, with an external USB drive, this time with two different units, El Capitan and Sierra. Same results.

-Internal (mechanic) HD extracted and checked with Disk Utility and Disk Warrior. Perfect. Zero problems. Even I started a Mac Book Air with it.

-Startup using Apple Hardware Test (AHT). It tolds me it has an error (4SNS/1/40000000: TH00-9.000). It seems to be a thermal sensor, but all sensors are present, and seems to be fine. Except when I removed the internal HD, of course; when you do this, you remove the HD thermal sensor when you remove the HD.

-Of course, CMOS battery checked and changed.

-I was told by the owner the machine was working perfectly until this suddenly happened (included the pink vertical bars in the screen, which leads me to think it probably was a video card problem).

I'm really lost. This is the very first time I have such a problem. Before, I always be able to start any Apple with an external drive.

Any help will be greatly appreciated.

[piernov]

Re: iMac A1311 extrange behaviour

Hello colleagues:
-The screen presented pink vertical bars. I have done a VGA chip reballing. Succeed. No bars. Clean screen at startup. This problem is solved.

No.

[fichamba]

Re: iMac A1311 extrange behaviour

No.

Sorry, piernov. What do you mean with "no"?.

Thank you.

[Jhkh]

Re: iMac A1311 extrange behaviour

How long do you warranty your jobs?

[fichamba]

Re: iMac A1311 extrange behaviour

How long do you warranty your jobs?

Sorry? Are you joking me?. All the repair works here have a warranty of 6 months. The law says 3 months, but we give 6.

I am being serious, I'm not joking. The pink bars dissapeared after doing a full reball in the (terrible) VGA card (I mean, VGA chip).

Must I understand that piernov is saying "no" to this part of the repair?. Maybe he's saying that video card is still giving me problems?.

As I said before, I never found a Mac which wasn't enable to start up from an external disk...

[fichamba]

Re: iMac A1311 extrange behaviour

No.

...maybe you mean "no; you think it's fixed, but it is not...video is still the problem"?.

[reformatt]

Re: iMac A1311 extrange behaviour

Piernov is right.

A lot of issues with graphics processors are bad connections from the die to the BGA pads. This is why they seem to come good after application of heat, and this is why a lot of people believe that a reflow or reball has solved the issue. The original fault returns sometime down the track. It's simply not worth the hassle.

[Jhkh]

Re: iMac A1311 extrange behaviour

Even if it revives those for a year or two, it's not reliable as you just found out and can be totally random. Here is an eight years old video that still holds true (laptop oriented, but still applies to affected iMacs).
https://m.youtube.com/watch?v=1AcEt073Uds
We deny those for years now, but some people are installing modded MXM Nvidia cards (this has some drawbacks like no boot screen or brightness control amongst other things for 21" and can necessit mods to the heatsink so we don't offer that to customers).

[fichamba]

Re: iMac A1311 extrange behaviour

Reformatt, Jhkh et all: thanks a lot for your comments. I was afraid of the same. That’s the reason why I have done a full reballing, not a reflow. Last week I refused to repair another laptop due to a curvature in the microprocessor. Impossible to reball a component with 0,4 mm balls with a higher curve in the center.

Anyway, the behavior is really extrange, because in spite it will fail as time passes, now is working. Maybe it fails when the system loads some kind of video resource…

Anyway, thanks again. It is not the first time I fix one of this (I hate these small video cards).

[jons]

Re: iMac A1311 extrange behaviour

That's the reason why I have done a full reballing, not a reflow. Last week I refused to repair another laptop due to a curvature in the microprocessor. Impossible to reball a component with 0,4 mm balls with a higher curve in the center.

Reball never ever worked on these problems (for longer than 1-3-6 months that's it), and that problem is more than decade old, don't rely on youtube or other internet gurus.

(I hate these small video cards).

Who don't

[radear]

Re: iMac A1311 extrange behaviour

Normaly this issue comes from grafics card.

[fichamba]

Re: iMac A1311 extrange behaviour

Thanks jons & radear.

[Jhkh]

Re: iMac A1311 extrange behaviour

Reball and reflow do exactly the same thing. They reconnect temporarily the bonding, for an unknown period of time. So you don't fix anything when reballing, GPU is still dying.

[fichamba]

Re: iMac A1311 extrange behaviour

Reball and reflow do exactly the same thing. They reconnect temporarily the bonding, for an unknown period of time. So you don't fix anything when reballing, GPU is still dying.

Indeed. Not for the small ICs, but that's for all chips with a “PCB” as base. They didn't support too much heat for long time. The same with microprocessors.