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My heated bed shut off in the middle of a print, and now won't heat up at all. The hotend works just fine.

I took a volt meter to the pins:
12 volts at the Rambo's A inputs (heated bed power) as well as the other two (though one of the bed power wires was corroded and a bit melted. The block was very slightly melted, but still seemed functional. I redid that wire, made no difference)
12 volts on the pins that come from the back of the power block and are soldered into the Rambo board. (to see if the screw terminals broke from melting)
Polarity seems to be correct as well.
All three fuses have continuity.

With the heated bed attached:
No voltage on bed output when bed is on, led6 very very briefly flickers on at first.

With the heated bed leads removed:
Resistance across the heated bed wires was... I forget, but it seemed reasonable.
Voltage on the bed output was 2.7 volts and led6 stayed lit.


I should note that I modified the firmware for e3d's cyclops hotend, but I had been running on that for a few months. Mainly, I just changed some pin assignments, but not the bed's pin. The printer itself is about a year old.
My suspicion is that something broke on the controller, but I wanted to see if anyone had a better idea before I buy a replacement. Thanks!

If you broke something, my suggestion is to check the fuse for the heated bed, the large automotive fuse, which you should be able to visually check, then if that's not the issue, pack it up and send it to Ultimachine for repairs. They seem to be very reasonable about repair prices. Especially with a partially crisped power input.

Not sure what to think now. The 15 amp fuse was fine, and it turns out the bed output puts out 12 volts if you actually set the temp high enough that pwm doesn't kick in (oops).
Additionally, the bed output can power a pc case fan just fine. I'm measuring a bit of resistance though the corroded part of the power block, so I'm going to replace that and see if that solves things. Good thing the rambo's design is open source and I could just pull the part number!

I'd also trim and re-strip the heated bed wiring that went into the compression terminal block before you put it back together.

g.

Thanks guys, I replaced the screw terminal and everything works now. The bed heats up noticeably faster too.

Incidentally, since I had a hard time finding it, this is the part I needed http://www.mouser.com/ProductDetail/Molex/39530-0006
Don't be fooled by the picture, it's the 6 pin model.

mrb_255 wrote:Thanks guys, I replaced the screw terminal and everything works now. The bed heats up noticeably faster too.

Incidentally, since I had a hard time finding it, this is the part I needed http://www.mouser.com/ProductDetail/Molex/39530-0006
Don't be fooled by the picture, it's the 6 pin model.

Thanks for the part reference, it's great when the part number and source is included!
By the way, what did you find was the easiest way to remove the old part since there are 6 soldered pins.

That part is just the press fit screw terminal side, I didn't mess with the soldered on bit since it looked fine. Seems like it would be a royal pain though. Looks like the manufacturer's part number for that guy is 39532-1006.

https://github.com/ultimachine/RAMBo/bl ... MBoBOM.txt
That's the list I'm pulling all this from.