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 Post subject: Solder ball theory
PostPosted: Thu Dec 15, 2016 7:12 pm 
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As I had posted in another thread, the iMac that I replaced some caps in started to show
video issues as I was stressing my repairs with Handbrake.
I figured the video card was either over heating or is frying, so I looked around and came across
some info on "reballing" the solder underneath the graphics chip.
One video shows the process and it seems successful, but there really isn't any follow up
info on whether it was a permanent fix or temporary.

What's the collective consensus that a over heating graphics card causes the solder balls underneath
the chip to loosen and loose contact causing the video to go awry and that spot heating the chip
reflows the solder ?


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 Post subject: Re: Solder ball theory
PostPosted: Fri Dec 16, 2016 2:34 am 
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Very tricky to get the heat (amount, duration, and localisation) right, I suspect.

Only worth trying as a last resort? - to possibly revive an otherwise dead card.
Surely also, this is only done on a removable graphics card (e.g. put it in an oven etc.) - not an entire iMac?

If it actually works, then I guess you count yourself really lucky, and I also guess it would be a permanent fix - until it goes again in a few years!


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 Post subject: Re: Solder ball theory
PostPosted: Fri Dec 16, 2016 9:19 am 
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Usually the re balling at home methods can work temporarily but are not permanent.

I used to repair XBOX's by re balling with some of those methods.
Wrapping the unit in a towel to overheat, using a hairdryer, heatgun, or even putting it in a oven with other parts of the board covered with foil. While sometimes they would work and make the unit last a little longer. More times than not it would fail again after a few weeks/months or hours of use. Best bet is to find a local repair shop who many be able to reflow the BGA chip. Fortunately for me we have at BGA re-flow machine at work that I have access to. I repaired my old 12" 800mhz G3 ibook with it back in the day. Good Luck!

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 Post subject: Re: Solder ball theory
PostPosted: Fri Dec 16, 2016 1:39 pm 
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I was going to try sticking my late 2009 iMac's graphics card in the oven. It has only been able to boot in safe mode since June. I just haven't had the time to give it a try.

Some repair shops abroad actually have the graphics card I need and new, but prices and shipping are currently too high so I'm doubting about waiting to see if those prices come down or sticking the card in the oven.

The problem is that I don't have the time right now to sit down and take it apart.

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 Post subject: Re: Solder ball theory
PostPosted: Fri Dec 16, 2016 9:59 pm 
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It would be quite possible to remelt solder in a 180º C or a bit higher, in an oven because that is about the melting point of solder. However at that temp, you may also be destroying the chips. If my computer was running at 180ºCelsius, I would be worried about its impact on the component chips.

But if it is a lost cause, trying the oven method may be worth a shot.


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 Post subject: Re: Solder ball theory
PostPosted: Sat Dec 17, 2016 2:37 am 
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An OK surface mount rework station and reballing kit with clamps, ball templates, etc., will probably cost $1000-2000 and you'd still need to learn how to use it. With such equipment you could, however, replace the chip and/or reball it with good confidence of success and the results would last.

Any other technique is unlikely to serve as more than a temporary fix. That said, the chips and the board shouldn't have any problem with the temps needed to melt solder provided you carefully control the temperature, don't keep the temperature at the highest point for too long, bring the temperature up and down uniformly across the board at an appropriate rate of heating/cooling, and that the computer is off when you're doing it. Or to put it another way, in order to solder chips to the board in the first place they had to get that hot. The trick is doing it uniformly and precisely controlling the heating/cooling/max temperature.

Not all the components are actually soldered down, so you'd need to remove everything that isn't soldered down and/or that could melt. One thing that could make this easier is that I think the video card in your model iMac may be just that, an actual (removable!) card just like in the Before Times. No promises there. If it is, it'll be a lot easier to get uniform and precise temperatures, plus if you fry it you can just buy a new one for probably a lot fewer $$$ than a new motherboard.

I don't remember the precise problem with that model, but if the solder joints are the problem then re-balling them should fix it; merely reflowing the existing solder balls might help, but probably won't permanently solve it because solder balls just don't really reflow very well. If it's the chip then you'd have to replace the chip.

All that aside, consider that the problem could actually be a power issue: you know it had bad capacitors so it's reasonable to suspect one or two bad ones remain, or that perhaps some of the new ones aren't making good electrical contact. Be sure to look at the bottom of the capacitors as well as the top because they can bulge on either end, but bulging on the bottom isn't as easy to see at a glance. I'm also not quite convinced that capacitors which aren't bulging are necessarily working within (or even close to) specification, and it's plausible that errors might only appear under heavy load.

- Anonymous


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 Post subject: Re: Solder ball theory
PostPosted: Sat Dec 17, 2016 9:16 pm 
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Runs OK in safe mode...
Running in Safe mode leaves out some video drivers. Which results in your machine not using advanced video hardware. As luck would have it, you can run the safe mode video drivers in normal mode.

Here is how:
https://discussions.apple.com/message/16057567#16057567

Look through the above thread. See the second page. You don't have to read through the first page. Just go to the part where I try a solution that works.

Using the safe mode video driver results in these limitiations:
-- OpenGL acceleration is not supported on this mac
-- Your mac lacks quartz extreme acceleration



Robert


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 Post subject: Re: Solder ball theory
PostPosted: Sun Dec 18, 2016 12:31 am 
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rccharles wrote:
...you can run the safe mode video drivers in normal mode...

Thanks for this suggestion. I've needed to do this before and for some reason never actually done it.

This may, however, only be a stopgap if the chip really is acting up. On the other hand, if it stops the gap long enough it might not matter that the chip may croak eventually.

- Anonymous


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 Post subject: Re: Solder ball theory
PostPosted: Tue Dec 20, 2016 6:59 pm 
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Seems very odd to me that the reballing would work at all, looking at the iMac's graphics board the
area underneath the chip is densely populated with fly poop sized components.
Heating the chip till the awful no lead solder flows ( it doesn't ) would possibly loosen those
components underneath effectively making the board domestic land fill material or foreign land fill.

I did clean and reapply fresh Arctic Silver 5 and thermal interfacing, and the artifacting has gone away
but I am now experiencing spinning beach ball lags, even as I type this.
It's worse going to web pages where I'm trying to order materials.

I'm also running smFanControl and Hardware monitor, what is a lethal temp for a graphics chip ?
I see posts in overclocking forums of 60C as being chip killing temps but I can't seem to find any official
docs from nVidia.


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 Post subject: Re: Solder ball theory
PostPosted: Wed Dec 21, 2016 12:28 am 
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I couldn't find any official documentation on the 7300GT, but unless there's a design defect I would be surprised if 60C would kill them. I'd bet their thermal limit is closer to 90 or 100C. Of course if there is a design flaw that causes them to crack apart when they're thermally cycled, then the rated temperature probably isn't very useful anyway since it probably presumes the engineers did their jobs.

- Anonymous


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 Post subject: Re: Solder ball theory
PostPosted: Wed Dec 21, 2016 7:38 am 
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Apple's thermal engineers have been standing in the corners for years while the Quiet engineers do their job.


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 Post subject: Re: Solder ball theory
PostPosted: Wed Dec 21, 2016 7:51 pm 
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BDAqua wrote:
Apple's thermal engineers have been standing in the corners for years while the Jony Ives steals their job.


Fixed that for you.

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 Post subject: Re: Solder ball theory
PostPosted: Wed Dec 21, 2016 8:00 pm 
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:D


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