Hotbed suddenly stopped working

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Joined: Wed Apr 09, 2014 9:58 pm

Hotbed suddenly stopped working

Post by ketil » Wed Jan 09, 2019 12:27 am

I have a classic M2 with the dual power supply. I was happily printing on Sunday, but on Monday the heated bed didn't warm up, and it hasn't had any effect whatsoever since. I turn on the heat, and then there's no change in the temperature.

The external big PSU for the heated bed (12V 18amp) has an LED displaying power status, and this LED is on. I haven't ruled out that it's dead though - but I don't know why this would be the case.

The big PSU seems to be well connected to the RAMBo. Like I said, it worked the day before, and I haven't moved anything.

I inspected and replaced the 15amp automotive fuse on the RAMBo, but this didn't change anything.

The connectors from the RAMBo to the heated bed seem to be inserted ok.

What am I missing? Has something died on the RAMBo? Is my big PSU dead? If so, what's a good replacement? Or do I need to dig up my voltmeter and start measuring to figure this out?

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Re: Hotbed suddenly stopped working

Post by ednisley » Wed Jan 09, 2019 2:45 am

ketil wrote:
Wed Jan 09, 2019 12:27 am
What am I missing?
Rummage around here and you'll find platform heater failures galore, particularly on early M2s with 12 V platforms. The basic problem: too much current for the connectors.

Pull each of these connections apart and check for charred connectors:
  • PSU to RAMBo
  • RAMBo to platform cable
  • Platform cable to platform
Disconnect the cable at the platform and, assuming the connector pins are OK, measure the heater resistance, which should be a few ohms. If it's "infinite" = open, then the heater has failed. Some folks have been able to splice around the break, but I'd call it an opportunity to upgrade to a 24 V platform.

It's also possible to have a wire between the RAMBo and the platform break from fatigue, so, if you find nothing else, take the wires out of the braid and search for obvious failed sections; they'll look frazzled.

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