Bed not heating, have tested everything I can think of!!
 

[Solved] Bed not heating, have tested everything I can think of!!  

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Nick R.
(@nick-r-2)
New Member

So I have a MK2.5, with a 12V MK52 bed and everything was working great for the last year!

About 3 weeks ago, the bed wouldn't heat up and I traced the problem to a partially melted PSU -> Rambo Bed Wire Molex. Today I replaced it and I now have the bed is still not heating up, I made to following measurements with the multi-meter:

Bed Resistance (no wires): 1Ω

Bed Resistance (with wires): 1Ω

Bed wires from Rambo not connected to bed (and bed set to heating) voltage: 12V (11.6)V

Bed wires from Rambo connected to bed (and bed set to heating) voltage: 0V (no bed light)

PSU Bed wires voltage: 12V

PSU Bed wires connected directly to bed: Bed is heating up (light is red)

Bed Thermistor: shows correct ambient temperature. Rises when rubbed (heated up with blow drier)! 🙂

There are no physical evidence that something is fried on the Rambo. Latest firmware. (also tried previous firmware and firmware reset "All" and firmware update to the latest).

Any ideas are appreciated! 🙂

Nick

P.S. I am currently thinking of using an external Mosfet to drive the current to the bed (since it is sending 12V when not connected to the bed) , but I'm trying to exhaust all ideas first before "hacking" with the printer.

P.S.2. checked the wires from board -> bed don't see anything, checked fuses...all ok and wires have continuity.

 

Posted : 24/02/2021 3:41 pm
Nick R.
(@nick-r-2)
New Member

Apparently the connector on board from board->bed has melted internally and even if I had replaced the molex from the cables end, it also needs replacement of the connector on board... (removed the positive cable, turned on the heat bed and touched "VERY CAREFULLY" the bottom BED+, and the bed lit up.. A close photo reveals of the connector reveals the ugly truth..
So I guess the soldering iron is heating up and a new connector must be installed!! 🙂

Posted : 25/02/2021 11:03 am
cwbullet
(@cwbullet)
Illustrious Member

Check you wires and the attachment points to the bed.  Mine becoem loose and cause a similar reaction at the bed.  I wonder if this happened with the connector on this end.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 25/02/2021 11:08 am
Diem
 Diem
(@diem)
Reputable Member

@cwbullet

If the connector is not pushed home properly or if it is dirty/corroded there can be sparking and if it's carrying a high current it will get hot.

A reminder to check for loose connections as part of regular maintenance.

Well traced @nick-r-2, at least it's a big enough soldering job that you don't need a microscope.

Cheerio,

Posted : 25/02/2021 5:33 pm
cwbullet
(@cwbullet)
Illustrious Member

@diem

I concur.  I also burned up a Rambo board due to a lose connector.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 26/02/2021 12:40 am
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