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Prusa MK3 heatbed power cable shorted out (on the Einsy side) and it looks like I need to replace the Einsy. Should I replace the heatbed too? I don’t know electronics well and am worried I will just fry a new Einsy.

Heatbed end: Heatbed end

Crispy at RAMBo end: Crispy at RAMBo end

Crispy at RAMBo end: Crispy at RAMBo end

Larger images can be found here.

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There should be no need to replace the heat bed. It wasn't subjected to any unusual loads.

If the bed isn't heating, there could be one of sever problems, but I would start with the fuse. If the fuse had time to do its job, it would have blown and protected the circuitry. In your picture, the fuse is the blue component with "15" stamped on top. There are also two fuses with "5" stamped on top. One of these may be blown. If so, replace it and try again.

If the fuses are all good, and everything except the heat bed works, you have probably blown the FET that switches the heat bed power. If you aren't handy with circuit board repair, you may choose to get an new Einsy controller and then try to repair your old one. These repairs aren't usually hard because the FETs are fairly large components.

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I don't think that the heated bed would be damaged if the connecting wire shorted out. The heatbeb is basically one large resistor. It has a couple of surface mount LEDs that lights up red when the bed is powered for heating, but there should not be other sensitive components on the board.

The greater concern I have from your attached photos, is the cause of the 'short'. Unless there was fraying or other loose wires that could have bridged the terminals, your problem might have been a loose connection that created resistance at the interface layer which then caused that specific connection to heat up. The voltage is not high enough to cause sparks across the gap.

The additional heat and electrical instability might have fried your Einsy. You don't mention if the printer starts when you power it up, but I assume that you are considering replacing parts because the printer is not working.

If you have access to a multimeter you can just measure the resistance across the wires of the heatbed. If it is broken you will see an open connection on the multimeter, but if you see Ohms in the 1-100 Ohm range (don't know the specific resistance of a disconnected heatbed), it means the board should be OK.

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You do not need to replace the heated bed. However, you should replace the damaged fork connector. What happened here is that the connector did not make a proper connection with the terminal block (perhaps due to the screw working itself loose) and heated up. There is no reason to suspect anything else is damaged, but the connector itself is clearly damaged. If you do not replace the connector, it may again make a poor connection and heat up.

Replacing the entire Einsy board is not strictly necessary. The only damaged component is the terminal block. You should consider soldering the wires from the heated bed directly to the Einsy, bypassing the terminals entirely. This is arguably a better solution since a soldered connection is more reliable than one using a terminal block. You can simply solder the wires on the back of the board.

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