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<== Date ==> <== Thread ==>

Subject: Re: mvme6100 HW issues?
From: <chris.colborne@diamond.ac.uk>
To: <tech-talk@aps.anl.gov>
Date: Wed, 1 Feb 2012 10:49:54 +0000

We have lots of experience of the MVME5500, which has a similar physical layout. The heatsink of most MVME models, including ours, is on the “wrong” end of the board for many forms of horizontal VME crates, which tend to blow air from left to right so it’s lost a lot of its strength by the time it reaches the heatsink. Without sufficient airflow they can get extremely hot in normal use, even when idle.

 

In the early days we experienced a very high failure rate, with a variety of different messages but mainly the end result was BFL, or the “yellow LED of Death” showing constantly. Sometimes the heatsink became hot enough to cause actual burns so beware! When allowed to cool down they could usually be restarted, but would fail again once hot. So we paid considerable attention to the airflow in the crate, including devising a baffle in slot 2 which channels more air over the heatsink, lowering the temperature by more than 10 degrees, and changed the crate design so that the crate’s power supplies would not block the air from leaving the heatsink area. But in the end Motorola admitted there was a PCB batch problem leading to failed microvias. Repeated warming up and cooling down caused thermal stress which allowed the bad vias to show themselves. Almost all the affected batch eventually failed, and I’m happy to say all were replaced. Since then, reliability has been outstanding, with only a handful of failures in 6 years with about 500 boards running now.

 

It’s highly unlikely that you have the same problem we had! I do have one slightly flaky 5500 in my test crate which reliably fails if allowed to get too hot, but is fine otherwise. Your heatsink should definitely not be loose – it is restrained with a spring clip but with the two screws fully tightened (on both sides of the board) there should be no movement at all. You may also need to pay careful attention to the airflow over the heatsink. In the datasheet there is a figure for the required airflow but how you’re supposed to know whether you meet the requirement is anyone’s guess.  If this board is still misbehaving with a secure heatsink and ‘lots’ of air, then it’s probably truly faulty – you’ve been most unlucky – enjoy the replacement!

 

Kind Regards,

 

Chris Colborne (Senior Technician)

Diamond Light Source Ltd

Diamond House

Harwell Science and Innovation Campus

Didcot

Oxfordshire

OX11 0DE

Direct tel. +44 (0)1235 778401

e: chris.colborne@diamond.ac.uk

www.diamond.ac.uk

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