Reassembled XOs fail heat spreader test

[Sridhar Dhanapalan]

Thanks Samuel. I'll be talking in more depth with OLPCA about this.

Any suggestions on how to deal with this in the meanwhile are welcome :)

I have found that it can help to bend the spreader near the screw
points to make it slightly concave. However, I agree with you that
this is not a good recommendation for deployments.

Sridhar



On 23 July 2011 12:18, Samuel Greenfeld <greenfeld at laptop.org> wrote:
> The "unused" hole actually is filled by one of the screws which holds in the
> rear plastic panel.  That's why the screw holes which only secure the heat
> spreader have arrows pointed at them.
>
> The fanciest (newest?) XO-1.5 heat spreader design I've seen adds a support
> bar up to the green screw hole above near your area of concern, again filled
> by a screw used to secure the back cover.  I'm not certain though if this is
> the design John is referring to, but I have seen a few XO-1.5s with it.
>
> It may be possible to bend the existing heat spreader in a certain manner
> which solves the problem.  But I would *not* be someone who could recommend
> this approach for deployments.
>
> Some of OLPC's hardware engineers may be traveling this weekend, so I'm just
> trying to provide you with a quick explanation in the meantime.
>
>
>
> On Fri, Jul 22, 2011 at 9:55 PM, Sridhar Dhanapalan <sridhar at laptop.org.au>
> wrote:
>>
>> All of the XOs I've seen have three screws on their heat spreaders.
>> I've attached an annotated image. Hopefully the lists don't strip it
>> out.
>>
>> There is an unanchored screw point in the bottom-left. However, the
>> danger area is at the top, particularly in the top-left. This affects
>> contact between the heat spreader and the Companion Chip, and might
>> also be affecting contact with the CPU. Do the four-screw versions of
>> the heat spreader address this problem?
>>
>> Thanks,
>> Sridhar
>>
>>
>>
>> On 23 July 2011 01:21, John Watlington <wad at laptop.org> wrote:
>> >
>> > Do your heat spreaders have four screws or three ?
>> >
>> > The final heat spreader for XO-1.5 production had four screws
>> > holding it down, to ensure a good fit.    If your heat spreaders
>> > only have three, OLPCA should be able to get proper replacements
>> > from Quanta.
>> >
>> > Regards,
>> > wad
>> >
>> > On Jul 22, 2011, at 10:35 AM, Sridhar Dhanapalan wrote:
>> >
>> >> We are currently engaged in changing the motherboards in over a
>> >> hundred XO-1.5s. In many cases, the XOs are failing the heat spreader
>> >> test afterwards.
>> >>
>> >> However, we can get the test to pass if we press down on the lid,
>> >> behind the screen. This suggests to me that the heat spreader is not
>> >> in proper contact with the chips.
>> >>
>> >> Without the lid plastic affixed (heat spreader exposed), we can see
>> >> that the spreader is not touching the chips properly. We have tried
>> >> bending the metal slightly near the screw points, but the contact
>> >> doesn't last.
>> >>
>> >> Is there any way that we can deal with this better? We are changing
>> >> the motherboards in these XOs because they have succumbed to
>> >> overheating. I want to avoid that from happening again.
>> >>
>> >> Thanks,
>> >> Sridhar
>> >>
>> >>
>> >> Sridhar Dhanapalan
>> >> Engineering Manager
>> >> One Laptop per Child Australia
>> >> M: +61 425 239 701
>> >> E: sridhar at laptop.org.au
>> >> A: G.P.O. Box 731
>> >>      Sydney, NSW 2001
>> >> W: www.laptop.org.au
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>> >>
>> >
>> >
>>
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