Pin on Rambo card getting VERY hot

I have a problem with one of the hot bed pins on my Rambo board getting extremely hot (I can't touch it at all). I am now on my third female connector and it is starting to bubble up as well. I have replaced the wiring to the bed with heavier (18) wire, inspected the male pin VERY closely, cleaned it and I can't seem to figure out why it is getting so hot. The fact that the pin looks every bit as good as any of the other pins in that male header, and that I have gone through several new female plugs, is baffling me. The bed seems to be operating correctly as far as I can tell. The only thing that I can see is that the solder joint on the bottom of the board for that pin is a bit discolored (duller than the reast), but I think that is more a result than a cause of the problem. Also, at the risk of giving away my ignorance, electronically speaking, I can't understand why it is only the one pin that is getting that hot. The other pen on that same female plug seems to be fine.

Has anyone had this issue with Rambo, or Ramps boards?

Medal Perusa i2, Rambo, MEK3 Mini extruder and j-head, mk2a (china) bed, Marlin.

Charlie

Could be a dry solder joint, rework it and see if the problem clears up.

When you say dry solder joint, would that not be visible on the factory solder joint? Dry joint is a new term for me. By rework, should I assume you mean to remove as much of the solder as I can and then resolder?

Thank you for your response.

Charlie

Dry joint, usually means any bad joint, but it happens when the solder didn't flow properly onto the metal. Because metals usually have an oxide layer, you can get solder on the pad and surrounding the pin but not making a good contact.

You can usually fix a dry joint by applying soldering iron, but most importantly adding some new solder as this provides new flux, helping the solder to make metal to metal bridge. In extreme cases I would remove existing solder with a wick or sucker, and start again.

Those connectors should be good for 15A, unless your heatbed is drawing too much, but then I would expect to see some blown fuses. Does the fuse get warm?

No nothing seems to heat up except the one side of the bed female plug (and I guess the male as well).

I will try wicking and re soldering and see if that works. Thanks.

I had some heat generating to once, but that was becase of to smale(to little cross section, mm^2 SI, AWG Imperial) wires from the ramps board heatbed ports too the psu.

If only one of the pins gets hot, then it could be one of two things:

1. The component connected to that pin is getting hot, and that heat is adding to the heat generated by the current through that track/pin.
2. The pin that is not heating up has some alternative method of avoiding current. This could be a wire that is connecting the heat bed back to the PSU directly, a short between the heatbed and it's thermistor, or even a short to the frame of your machine that also connects somehow to your electronics (eg: if the PSU or electronics are mounted on the frame).

Q1. Which side of the heated bed connector is getting hot? The one nearest the capacitor, or the one nearest the other outputs?

(I'm using this for reference: [github.com] )

Q2: There is a FET between the Mega 2560 chip and the heated bed connector (controls the heated bed output). Is this running very hot? I would also consider re-soldering that if so, and maybe make sure it has a fan on it.

Q3: Which heated bed do you have and where did you get it?

Note: A pic of your bed/wiring might be a reasonably good idea

Problem solved thanks to you all. The pin was the problem. I removed the factory solder with wick, fluxed it real good and resoldered. I also cleaned the post again real good and changed the female plug again. Just did a two hour print and it stayed cool the whole time.

Thank you very much. And now I know about "dry joints" I already new about crunchy joints (in my knees) but this seems to be more curable.

Charlie