Heated Bed not Pre-Heating

My printer has been working fine for a while but now the heated bed will not heat up. I can control the X, Y, and Z axis manually and the nozzles heats up. So far only the heated bed seems to not be working. Any suggestions?

 

I had the same issue and it turned out to be a worn out wire on the bed. Since it moves back and forth, the wire broke.

I asked about it and they suggest a replacement of the kapton heater and thermistor for the extruder.


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Bjorn do you see a temperature for the bed?

 

Yes I do. I normally see ~22C on both the extruder and the print bed when I turn on the printer.

 

Either a loose or damaged connector. Check the plug under the glass

 

Hi Mike,

I finally checked the plug and was told by Robo3D to actually remove it completely and solder the wires together. I did that but it didn't help. Upon further inspecting the board I found that one of the power mosfets (IRF3205) had heated up enough to de-solder itself. I re-soldered it and started the printer up again. The heated bed now worked but within a minute the mosfet had desoldered itself again. Any idea what could be causing this overheating? I soldered it back in the same orientation as the other mosfets.

 

Wow, for the mosfet to heat up that much it must be pulling some serious amps. Either that or it's defective.

To begin I would swap in a new mosfet. I'd also measure the resistance coming off of the bed heater. It should be around 1.4ohms of resistance.

The circuit for the bed is pretty simple. Pin switches the mosfet and then there's a polyfuse in front of the mosfet.

 

It's reading 103K ohms which is certainly higher than 1.4 ohms!

 

Are you sure you're not reading the thermistor?

 

Good catch! We are reading 1.2 - 1.3ohms. Still suggest changing trying to change the mosfet then?

 

yeah they're pretty cheap. There might be some ways to troubleshoot it to see if it's faulty but that's out of my understanding. It should not get anywhere near hot enough to melt solder, that to me indicates failure.

 

We replaced the mosfet with a new one that is the same as the original. Still cannot get the heated bed to warm up though although I have control over everything else. Any ideas?

 

I guess I'll start w/ the question of: Are you sure the mosfet is installed in the correct orientation?

I'll assume you did, but gotta ask these things.

The heater circuit is pretty basic: http://reprap.org/mediawiki/images/f/f6/RAMPS1.4schematic.png

D8 triggers Q3 over a resistor which is a pull down mosfet. When the line is dropped to ground an LED will light up and the heater will receive voltage.

Best way is to follow 12v from the input and see if you can find a burnt trace or something that would show where the connection is being lost.

 

Yeah buying a new ramps board is the quick and easy test fix, though its good habit to isolate the issue. Just in case it is the Arduino that's faulty (unlikely)

 

We can't see any burnt traces on the board. At this point I think we're going to ask Robo3D to send us all new boards because this is taken wayyyy too much time and we need our printer running. Mike can you put us in touch with someone who can help? So far it takes forever to get any action from Robo3D support.

 

Use the replacement part request form on the main page. http://www.robo3dprinter.com/pages/replacement-part-request

It will take them a while but they will deliver. I suggest you just buy a new ramps/arduino combo while you wait on the replacement.

 

Thanks for the info and your help! At this point, it doesn't make sense for me to have to buy new parts to fix a printer that should work. I'll submit the request and we'll go from there.

 

I understand, just letting you know the current state of things. If you're fine with having to wait 2 weeks and go through all the troubleshooting again, then that's your choice.

Me, I'd rather spend the 20 on a new ramps while I wait on them.