Yeah, mine was totally fried, but just on the one pin. I haven’t looked at the board schematics in detail to see where the flaw is, but once that pin starts failing it likely just gets worse and worse as the increased resistance causes it to heat up more over time. Clearly that fuse is basically ornamental, though, because I’ve seen plenty of fried board connectors, but never a blown fuse. I did notice that I had signs of arcing behind the pin against the case. One cause might be that it can arc from the positive pin to the grounded bare-metal of the case, which can cause a failure like this over time. You can see in the image I posted that I applied some kapton tape behind the Rambo before I reinstalled it.
I just noticed that your board might be a different version from mine as well. I think they had maybe 5(?) revs of the rambo. Probably should have pointed that out above. 
I didn’t notice any spatter on mine. Although the way I knew something was wrong was that the same pin was pulled out of the board. The other pin is still good and my motherboard resembles the OP’s, although the connector was completely torched 
Also, I just finished running two different 10 hour prints and was about 10 minutes into an hour print. My guess is that this is something that has been burning over time and wasn’t spontaneous in my case.
The board says its a 1.4a, thought there were only 1.3./1.4 for Taz 6 generally but I’m new to Lulzbot. My motherboard for my computer does not have tape between itself and the case, I’ve run my own computer for a decade at least now and have never had any issues. I’m guessing there’s a flaw in the design of the board, especially since multiple people in this thread have experienced the same exact problem (highly sus).
Here’s the link to the connector I bought for anyone else that might need this:
2 position Molex connector
Before the rest of the connector broke off, I was able to test the connection by holding the connector in with a plastic piece I printed (super not safe). I was able to see the bed heating up, so splicing into the fuse works as you described.
Replaced the molex connector and I’m back up and running! Bed is heating and cooling as expected. Thanks again @intelinc !
I just ran into this same problem on my home-built TAZ 6 clone (using the control box from the TAZ 5).
The round connector on the control box that the bed harness connects to melted. Will have to find where i can order a replacement. In my case, the terminal block connecting to the RAMBo and the RAMBo itself were both totally fine, but the symptoms were identical to the OP’s.
The TAZ 5 has been known to wear that connector and we have a passthrough harness for the bed that completely eliminates the potential for this issue.
Thank you for the link, @McLeach, that’s quite helpful! I actually did find that in my subsequent searching, as well as the Ohai installation instructions, so I figured I wasn’t the first person to run into that issue. I actually had some extra crimp pins and connector housings for both Anderson PowerPole and Molex 2-pin connections laying around, so I ended up staying up late last night and crimping myself a new heat-bed cable harness and connecting it directly to the control board. Problem solved!! I’ve got some Ninjaflex loaded up, so I’ll look into printing the strain relief next.
I also took the opportunity to replace the RAMBo 1.3L with an Archim 2.2 board and am super happy with how it’s running so far!
Hmmm, I have a Taz 6 with a bed that doesn’t want to heat anymore. I have read through this thread and have tried a few of the things suggested.
I have examined the backside of the RAMBo and the molex for the bed heat and do not see any burn marks. I get a solid red LED and a flashing red LED when I try to heat the bed. When that fails, the blinking red LED goes out.
I ran a heavy gauge wire from the positive (right) bed heat wire to the negative (left) fuse connector. The bed would still not heat.
Any other things I can try? Buy a new RAMBo?
My first suggestion is to start a new topic… This one was started in 2017 (5 years ago) and the title says “…SOLVED…”.
More importantly is why that burned out. Could have been a weak solder joint, but make sure nothing’s wrong with your heater before burning another one out.
Sounds like these rambo boards should be using smaller fuses or more power wires. 15amp fuse on the bed heater seems a bit much when those pins are rated for just a few amps each. Has anyone actually ever blown a fuse on the rambo before frying a board or psu?
