UGTS Document #80 - Last Modified: 8/29/2015 3:23 PM
HeatSink Detection Failures on Dell Desktops and Servers

Older Dell desktop and Server machines (around year 2003) have a metal 'Z' clip that holds down the heatsink on the board's chipset so that it stays firmly attached to the chip.  The motherboard knows that this clip is attached because the Z clip is bent down like a spring between the heatsink and two metal 'U'-shaped loops on the motherboard.  The motherboard looks for an electrical connection between the two U loops.  If there is no connection, it assumes that the Z clip is not attached and that there is therefore nothing holding down the heatsink.  If this happens, the BIOS will stop the machine from booting with the error:

Alert chipset heat sink not detected.  System halted.

This error message cannot be bypassed.  If the Z clip is loose, you cannot boot the server.  Unfortunately, the Z clip can come loose due to reasons outside your control, such as the U loops popping off the motherboard under the spring force from the Z clip.  This is a known problem on the Dell Dimension 4600 desktop machines, but in rare cases also with some servers, such as the PowerEdge SC1420.  This article describes a workaround.

The Z clip, detection mechanism, error message, and refusal to boot is a good thing.  Without the Z clip, the heatsink can fall off the chip when the chip gets hot and melts the heatsink thermal paste, and a fried chipset equals a dead board.  However, the flimsy construction of the U clip is not good - there is no good reason why it should not be more firmly attached to the board.

When I encountered this problem on a Dell PowerEdge SC1420 server, one of the U loops had popped off and was lost for good (or bad).  The Z clip was sitting on the bottom of the inside of the serer case, and the heat sink was still attached to the chipset.  I took a thin paper clip and bent it into shape with pliers to be the right width (according to the holes in the board where the U loop used to sit).  I then cut the paper clip to the right length and smashed the ends of the little U loop I'd constructed with pliers to make them pointy.  I then shoved that pointy paper clip section into the holes in the motherboard until it was in there firmly and I could not easily yank it out by pulling on it.  Then I soldered it in to be more firmly attached, and to make a good electrical connection with the board.  Then I put the Z clip back under the one U clip that was the original one and my replacement.   Then I used a DMM to test that the electrical connection between the two U loops was good.  After that, the system booted fine.

However, if this happens to you, be sure to have isopropyl alcohol, paper towels, and thermal paste handy.  It's very easy for the heatsink to come off without the Z clip retaining it, or when you're trying to put the Z clip back on.  You don't want to get stuck with an unbootable server because you can't paste the heatsink back on to the chip.  In fact, if you maintain any servers, it's a good idea to always have these three things handy in case of emergencies.