Heatbed Terminals Destroyed  

RE: Heatbed Terminals Destroyed

Can't see what's under the metal sheet (no x-ray vision).  But this clip shows what is supposed to be there.  I don't quite understand how the copper was burnt off well away from the screws.  Did you remove it, or is this photo exactly how you found the connection?

IF -and it's a huge if - you can see the copper trace that's under the metal sheet, and access it well enough to solder, you MIGHT (huge might) be able to jury-rig it... but if it were mine, I'd already have a new bed on order.

RE: Heatbed Terminals Destroyed

PCBs can be repaired, of course. The OCD method is to scrape off all the debris, use high-temp epoxy to glue an ultra thin copper sheet back where the pad was, scrape off the protective lacquer from the remaining trace going from the pad, connect them with a thin layer of solder and cover any metal that shouldn't be exposed with another layer of high-temp epoxy. If done with utmost care, the repair is almost invisible and functionally equivalent. Video HERE.

Now if you don't have the patience, simply chop off the terminals on the cable and solder the cable to any remaining copper on the board. Either the last bits of the pad or the beginning of the trace. Put a blob of RTV silicone gasket maker on it all and put the plastic connector cover back on. In 24 hours the silicone will have set and provide enough relief for the wires so the repair will not break off the trace again.

RE: Heatbed Terminals Destroyed

But you should also think about answering the question of how it happened in the first place? Liquid damage?

RE: Heatbed Terminals Destroyed

Posted by: Vojtěch

But you should also think about answering the question of how it happened in the first place? Liquid damage?

Looking at the enlarged picture: loosened screw, oxidation, high contact resistance, ohmic losses, heat, burning of the FR4 is the sequence of events.

RE: Heatbed Terminals Destroyed

Odd results.  I had my wire insulation melt.  There was a broken wire.  I replaced the wires.  

RE: Heatbed Terminals Destroyed

Posted by: charles.h13

Odd results.  I had my wire insulation melt.  There was a broken wire.  I replaced the wires.  

What is odd about that?

RE: Heatbed Terminals Destroyed

Thanks for the help guys!

As of right now, I have soldered a copper wire from what's left of the copper trace to the wire heatbed wire. It's working perfectly, but I eventually aim to either epoxy a new terminal on or replace the bed entirely. Anybody know where I can buy a new heatbed?

RE: Heatbed Terminals Destroyed

You can buy the original in the Prusa Shop. You need to be logged in to see it, but given you're posting in the forum, you probably are. Depending on where you live, you may find a shop that stocks Prusa parts in your country and save on shipping. Of course, there are plenty of knockoffs available on eBay, Aliexpress, Banggood and all the other places, too.

RE: Heatbed Terminals Destroyed

Posted by: david.g86

Thanks for the help guys!

As of right now, I have soldered a copper wire from what's left of the copper trace to the wire heatbed wire. It's working perfectly

Just make sure the copper wire is thick enough such that it doesn't heat up.

And, how about sharing photos of the fix in addition to the problem? It may help someone in the future.

RE: Heatbed Terminals Destroyed

Here's a photo of what I did if anyone is interested:

It's basically just an 18 guage wire stripped of its shielding fastened under the heatbed wire screw and soldered to what's left of the copper trace.

RE: Heatbed Terminals Destroyed

Posted by: Vojtěch

Posted by: charles.h13

Odd results.  I had my wire insulation melt.  There was a broken wire.  I replaced the wires.  

What is odd about that?

Well, first of all, why would they melt?  Unless there was a short, I can't figure out why the stock wires would melt.  

RE: Heatbed Terminals Destroyed

Posted by: charles.h13

Well, first of all, why would they melt?  Unless there was a short, I can't figure out why the stock wires would melt.  

When a stress breakage develops, it starts with a single strand of wire breaking. That makes the cable weaker at that spot, making the other strands likely to break there as well.

As the number of non-broken strands decreases, Ohm's law starts to show. The cable has an increased resistance (less copper to conduct the current) and starts heating up at the point of break. For simplicity, let's look at what happens when the cable reaches the point where it has the same resistance as the heat bed  (3.7Ω). Then half of the power sent to the bed turns into heat at the point of break. That's 38W at that moment (24V^2 / (2*3.7Ω) / 2) .

That is enough to cause a wire to burst into flame.

RE: Heatbed Terminals Destroyed

Thanks.  I am a little removed from college and high school physics.