Melzi overheat problem

I have a Melzi V2.0 running for about 3 years now, and I was doing some printing today, and I noticed what appears to be an overheating problem where the main power enters the board. I attach a photo.

The screw terminal block has melted, but the PCB itself looks OK. I have now unsoldered the block ready for replacement.

The PCB is on a RepRapPro Mendel 2 (Tricolour) - though I do not yet have the extra 2 extruders fitted and running.

Has anyone else experienced a problem like this ?

What could have caused it ? Arcing internally ? Faulty solder joint ?

You dont put soldered wires into those connectors, it forms a blob or weird shape and the contact only touches the bloby bits. Then all power flows threw the tiny contact area of the blob and heats up.

That's a common problem caused by tinning the ends of the stranded wire with solder before putting them in the terminal block. The solder creeps, so the screw becomes loose, you get a bad contact, and that generates a lot of heat.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for the tip.

I won't tin the ends next time.

The correct way to terminate stranded core wire in a terminal block for high-current connections is to crimp bootlace ferrules on them.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].