Heat Bed Problems

[BobenhamHotspur]

POSTS BELOW COPIED FROM OTHER THREAD AS THEY WERE OFF TOPIC

@Joao - Could I please ask for your electrical advice as my skills are very poor? (sorry for borrowing this thread for a moment)
My heated bed has stopped working and I am trying to avoid sending it back to China again until I'm sure it's a major problem that I cannot solve here. What simple tests can I do to check basic facts e.g. My extruder heater is working so if I plug the heater connector into the bed socket, is that safe? is there enough power to heat the bed? I really need to get this sorted soon as I have stuff to print for my grandsons birthday.

Hi Bob,
I would suggest you to buy a multimeter first
Even the cheap ones for £5 would help you a lot for any the electrical DIY.

You can swap the bed socket with the extruder, since the board circuit does not make any difference to which heat element it's giving power.
There are even 2 spares ones for additional heating elements (more extruders?) .
If you get the bed's relay burnt you could at least use a spare one and change the software settings. But lets find out first where the problem is and then act on it.

Another alternative to test (without the multimeter) you could wire any 12V light bulb that you might have at home.

I found that many people makes confusion with voltage (V) and power (Watt).
For example you can connect any 12V light bulb that consumes 1W to a power supply that says it is 12V 300W (12V 25A).
This means that the bulb will use 1W from the available 300W. Its not that the power supply will force the light bulb to take that amount of wattages/amperes. Its always the other way around, you just need to make sure that the supplier can take provide more than the total of itsconsumers.
Since the bed has a very high consumption, it is perfectly safe to test almost any small 12V device with a low W or Amp.

Feel free to start another thread to discuss and identify your printer problem.
I am happy to assist.

[BobenhamHotspur]

@Joao - Firstly many thanks for helping me out I asked Ethan to give me a list of things to try/test but he says the engineers don't speak English so he can't get this info, I only wasted almost 2 weeks waiting to find this out!!!

I have a multi-meter and have tried using it where I think I should, but I'm not 100% certain I touched the right spots and some of the results were a little confusing (to me anyway) I seem to have continuity on almost all connections between the bed and the board?

I have tried connecting a 12V 2Amp power supply to the beds wiring but there was no noise or obvious heating, but it's only 2Amp supply so maybe that's not enough?
I will try connecting the extruder connector to the beds socket tonight and let you know what the outcome is.

[McCrapShot]

I was troubleshooting my heat bed, and there are two points on the underside of the bed that you can get to easily to measure the voltage. If you slide the heatbed all the way to the Y-zero point where it hangs off the right side of the printer, there are 2 wires that connect to the bed there. You should be able to touch those solder pads to measure the voltage when the heat bed is on. This worked for me. When you're looking at the printer from the right side, you want to measure the voltage between the far right pad and the far left pad (if I recall correctly). I'd be happy to attach a photo of what I'm talking about when I get home this evening. You should see around 12V there when the heatbed is on and heating.

[Joao]

If you have a multimeter then this is another story

Start by testing the power supply, starting from the connectors on the board then going to the under bed connections.
With the power supply simply turned on (without the need of having the software heating up the bed), you can check if there is 12V providing energy into the board.

Check this photo where I highlight the dedicated wires that send 12V from power supply for the heated bed.
IMG_2376.jpg

If that has energy, then use the software to turn the bed heating on.
Check now the voltage at the connectors to the bed.

If everything has more or less 12V, then it could be a problem with the heating element under the bed.

To test that, I suggest you to use your Ohm-meter (in the multimeter select the Ω).
Then unplug the cable of the heat bed from the board, and touch with the multimeter connectors.
IMG_2373.jpg

Mine got stabilised at around 1.3Ω (it means the bed at 12V consumes 9 Amp and does 110 Watt).


IMG_2375.jpg

If you get a very very high number, or an unreadable number (the same as not touching anything, it depends on the multimeter how it displays that), it means that the heating element is an open circuit and does not have any resistance to heat up. It could have been a broken wire or the resistance got burned.

Let us know what values you get with your meter.

Good luck.

[BobenhamHotspur]

Hi Joao, thanks for the detailed stuff, unfortunately I have an unusually early start at work tomorrow so I'm off to bed now. I'll have a good read up of your instructions and test it out tomorrow evening.

[BobenhamHotspur]

@joao - I powered up the printer and applied the probes to the three pairs of connectors. The Main Pwr and HB Pwr both register a reading but the HB Out reads zero. I've attached a photo of the reading as when set to DC15V both readings went off the scale so I had to set it to DC150 for it to register. I assume that with no voltage leaving the board through the bed out wiring it is the board that is broken? Is it still worth me testing any of the other items you mention?image.jpg

[Joao]

Have you set the printer to have the heat bed ON ?

[BobenhamHotspur]

Have you set the printer to have the heat bed ON ?

Ah, damn it. It's set to zero at the moment but also I'm not connected to my PC. For me to check this I have to remove my printer from it's cabinet. I have a spare lead to provide power but I don't think I have a spare USB cable long enough to reach. I'll go and hunt for something.

OK pinched a cable from my scanner.

Trying again with PC connected and bed turned on = No change i.e. no reading on the meter - the LED light comes on though!

[Joao]

Another thing that you can do is to give directly to the bed the 12V from the power supply, during only a few mins, and check if it heats up. (Don't forget to disconnect if you fell heat, since there is nothing controlling the max temperature)
You can use the conector just next from it. Check my 1st photo and the lines I draw, if you connect them you are overriding the controler from the board.
it wont cause any problem to the board.

[BobenhamHotspur]

I put the HB Power into the HB Out. I now get a voltage? reading the same reading now on the meter as before when it was in it's normal connector but the bed does not heat up nor does the LED come on. Is this proving anything yet that I can report to Ethan?