Subject: CPU / cooling / torques etc
To: port-alpha list NetBSD <port-alpha@NetBSD.ORG>
From: Wilko Bulte <>
List: port-alpha
Date: 06/10/1998 19:08:54

as promised I paid a visit to the Digital repair facility to ask about the
heatsink mounting on an AXP CPU.

In talking to an expert :

- in the repair facility they use a small torque wrench
  This is done to really adhere to the spec, and to avoid goofups. Not
  every repair technician has 'sensitive' fingers.

- they always replace the aluminium nuts, just to be on the safe side. 
  Another guy might have overtightend them before. In a -hackers situation
  this should normally not be an issue.

- they also replace the Grafoil heat transfer sheet that is between the CPU
  and the heatsink. In my own experience (AXPpci33 & Jensen) the Grafoil
  was undamaged. Just handle them with care.

- enough torque is essential for a good heat transfer. Small wonder. 
  The heatsink is an overdesigned job, so there is some slack. Slack gets
  bigger when you add a fan. 

- don't overtighten, you can crack the chips enclosure. We obviously
  already knew this, but this guy saw real life examples. 

- LCA chips are not really known for their tendency to overheat with a
  sensibly 'torqued' heatsink. For hobbyist use a 'fixed is fixed' 

In summary: use common sense and there should not really be an issue.

Hope this info is of any use.

_     ______________________________________________________________________
 |   / o / /  _  Bulte 				  email: wilko @ 
 |/|/ / / /( (_) Arnhem, The Netherlands          WWW:
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