Duet 3 - Potentially defect fuse holder for OUT0

[eweilow]

As the title says, a (likely) defect fuse holder for OUT0 on my Duet 3 has resulted in a partially melted fuse and seemingly heat damaged fuse holder:


Additionally, the fuse holder is discolored. The metal in the fuse leg almost appear to have melted enough to move.

There is seemingly no other damage to the Duet 3 though, so the problem seems isolated to the fuse and fuse holder

This was noticed last week when trying to start a print. One print first failed due to a bed heater error (under-temperature). With fairly extensive cooling for small parts around the center of the heated bed, I've seen very short periods of under-temperature happen before, as the thermistor for the bed is right below the glass on the E3D Varipower bed that is used in the printer:

After the first print failed, I moved the print to elsewhere on the bed and uploaded it /started a new job after checking the printer for obvious faults, but this time the heated bed did not even turn on. Clearly something was wrong so I went on to check the status of the board. The LED indicating power for OUT0 was not on. At this point I had noticed that the plastic casing for the OUT0 fuse appeared to be partially melted, so I gently prodded it with a non conductive stick to check if it was soft, which by the small force applied caused the heater to turn on. After this point I shut off power from the board and have not turned it on since.

The printer is running OUT0 on 24V, with a 14A rated heated bed. Measuring the resistance of the bed at the Duet 3 screw terminals give a value of 2.1 Ohms, which at 24V should be a current of ~12A. Additionally, the actual fuse part of the fuse does not appear to be damaged and also has continuity:

Here are some additional pictures for reference.

Solder on the back appear to look okay still:

From "above":

OUT0 fuse holder is discolored:

Closeup:

OUT1 holder for reference:

It seems as if a bad connection between the fuse and the fuse holder is the cause of the problem, as the fuse itself has not blown, nor has the current been high enough.

This post was requested by E3D to troubleshoot and verify issues in order to process a warranty claim.

What other information would you need to determine if this is an issue that requires a warranty claim/replacement, or would it be possible to do repair of the fuse holder while not voiding the warranty?

Best,
Erik

[dc42]

Hi Erik,

Thanks for the photos. I approve a warranty replacement.

My best guess is that the OUT0 fuse was out of tolerance in respect of the distance between the legs, and this damaged the fuse holder when it was inserted. I've seen several 15A fuses that are out-of-tolerance in this way. We have changed the supplier of the fuses.