Heated Bed Dead?
So for the past few days I would randomly get thermal run away for the bed temp. However, the problem seemed to get worse and worse until now it no longer gets power and red led does not light up. I checked the following things:
I checked the voltage across the two solder joints on the bed when I set the temp to 60 and it registers at 0V. I disconnected the plug and measured the voltage on the pins on the rambo and it measured at 1.7V. I connected brand new wires (in case the plug was damaged internally) to the pins directly and tested the voltage again with them loose, 1.7V. If I touch those new wires to the heat bed solder joints it registers at 0V.
I've sent an email to customer support, but figured it wouldn't hurt to post here too. I've searched the forums but none of the topics/solutions seem to line up with what I'm experiencing.
The only changes I've made since I started seeing this problem was to replace my thermistor on my hotend (broken wire) and I upgraded the firmware to 3.1.0.
Re: Heated Bed Dead?
did you check the 15A fuse at the RAMBo with a multimeter ?
because either the fuse, or the MosFET is blown.
ps. it's very unlikely that the heatbed itself is defective. if you measure the resistance of the heatbed with a good multimeter, it should give you a value about 0.8 Ohm.
dem inscheniör is' nix zu schwör...
Re: Heated Bed Dead?
Just checked the 15A fuse with a multimeter and it shows it is good.
And my multimeter does hover around 0.8 Ohm for resistance.
Re: Heated Bed Dead?
ok, then the problem has to be located at the RAMBo board.
next I would check the solder joints of the heatbed connector, they might have "unsoldered" themselves when the connector got hot (due to a high contact resistance).
dem inscheniör is' nix zu schwör...
Re: Heated Bed Dead?
After completely disconnecting the rambo and removing it, it became apparent that the Bed Power In connector was burnt out. So it was the connector that comes from the power supply that was bad, rather than the one that connects to the heat bed.
I switched out that connector with a new one and the bed is now properly heating up again.
Re: Heated Bed Dead?
The connector that you replaced, what would you call it? I am having the same problem and having trouble finding a replacement part as I don't know what name to call it by.
Cheers
Re: Heated Bed Dead?
I have the similar symptoms as you, though I just finish building the printer, its brand new.
0.8 ohm Resistance from the printer bed,
0v from the bed terminals when the bed is heated to 50 c.
12 v from the RAMBO terminals when the bed is disconnected.
All fuses are ok.
So you think its the bed connector which has issues? or how can I further debug this?
Re: Heated Bed Dead?
Just in case someone else needs the plug to connect the 12v power to the RAMBo board, here it is:
Pluggable Terminal Block, 2 contacts 5.08mm (black)
Made by Molex
Here is Molex's page on it:
https://www.molex.com/molex/products/datasheet.jsp?part=active/0395300002_TERMINAL_BLOCKS.xml&channel=Products&Lang=en-US
Here it is in the Ultimaker store:
https://ultimachine.com/collections/electronics/products/pluggable-terminal-block-2-contacts-5-08mm-black
I think this is the same thing in the Prusa store:
https://shop.prusa3d.com/en/mk2-spare-parts/125-rambo-mini-heatbed-connector.html
My search for why my heatbed suddenly isn't heating seems to trace back to this connector being loose, too.
I haven't fixed it yet, but when I wiggled this connector, the heat bed started working again. I hope it's just the connector and not the soldered connections on the board…