I have seen several postings in forums about the power connector on some ender 3's being bad and causing issues or just burning out, potentially causing a fire.
How can I tell if I have the bad power connector?
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If you can measure the voltage at the main board where the bed power line is attached, or at the last point in the wiring prior to the connector, then measure the voltage at the bed, you can compare the difference to determine if there is loss related to a failing connector.
One certain indication of a failing connector is to separate the components of the connector and see corrosion, discoloration or any sign of burning. The Robo3d R1+ used 10 ampere connectors and the bed draws 14 amperes, according to the research I've done. When I discovered that information and separated the connector, it was an easy answer, as one side was scorched and the pins on the other were corroded and discolored.
Another method, not for everyone, is to use an IR camera and examine the leads carrying the power to the bed. The failing portion will be absorbing some of the power and heating itself, which will show up as a bright portion in the power path.
Unless the connector has already started failing - by getting warm, creating a voltage drop, eventually melting away -, you will have to remove the shrink tubing near it. Earlier batches had the connection crimped by the supplier of the cables, which is wrong. XT60 connectors should always be soldered to.
If the connector or the wires are hot, you have a severe problem. The heat of a high-resistance connection encourages additional oxidation and corrosion, which escalates the problem.
If the wires do not get warmer as they approach the connector, you don't have a problem, at least not yet. If the wires get warmer as you approach the connector, you probably have a budding problem.
Soldered connectors are not generally used, with crimped connections preferred. The copper-to-copper connection is lower resistance than copper-tin-copper. Also if something happens to the connector pins which cause them to heat (such as corroded surfaces), solder can melt.
Another answer suggests that the XT60 connector should be soldered. A quick look at some spec sheets show solder-cup connections which should be soldered and aren't suitable for crimping. I have not seen that there are no XT60 style connectors with crimp connections, so I can not rule out the appropriateness of a crimp connection.