Bed has stopped heating again
Hi all,
Well during a print awhile ago the bed stopped heating up. I played around with it and talked to support but for some reason the bed magically started to work again.
Now it has done it again.
I checked the fuses, all good. The voltage out of the power supply is roughly 11.89. But when I set the temp for the bed, I get the LED light on the Board and I measure the voltage at the terminal and I get 2.??. that isn't right. But when I plug the terminal in for the bed, I get nothing. The Board LED goes out and there isn't any voltage.
Ran the self check and says it's fine.
I did plug the bed into the hot end terminal and it will light up very briefly since it isn't supposed to go there.
I'm out of options here with this thing.
Not sure what else to check.
Any ideas?
Re: Bed has stopped heating again
May want to verify this test with others because I am only a novice with these type of things.
Here are things I would do:
I would think you should be able to hook up the the heated bed directly to the power supply but for a safe measure you may want to use the fuse inline pulled from the controller board.
This will tell you if there is a problem with power supply or the heater bed. If the bed is heating then the problem seems like it is software or the controller board.
Make sure you disconnect the power once the bed heats up to about 60c.
If the bed does not heat you can see if the bed will heat from another 12v power source. As long as you have a fuse inline I think you could even use a car battery since the internal resistance of the bed is fixed.
Also, have you used a multimeter to verify how much current is flowing the the heater bed.
Re: Bed has stopped heating again
Check that the heated bed connectors are fully tightend onto the cable. Loose connection will result in a high resistance and heating at that point and the lack of voltage to the bed.
Nigel
Life is keeping interested and excited by knowledge and new things.
Re: Bed has stopped heating again
Right now no voltage is going to the bed if it is plugged into the rambo. If the connector is not in the rambo then it only reads 2.?? which isn't correct.
I will check the other thing tonight.
Very frustrating and I love this printer. Been a main work horse for me since I got the original last december.
Re: Bed has stopped heating again
Hi Scott
It does sound like a RAMBo issue. Here's the circuit diagram:
Check you have 12V on the heater input from the PSU. It is the heater negative rail which is switched. The Schottky diode (D10) may be faulty or the mosfet could have blown. (I presume you checked the 15Amp fuse?) (The 2V when heater not plugged in could be leakage and very low current.)
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Bed has stopped heating again
Yup. Have 11.?? volts coming from the power supply. So that's good.
And the 15amp breaker is good.
Just very strange. happened on my other board too. And i did check it out too.
Thanks.
Re: Bed has stopped heating again
When this happened was it in a cold room, what was the ambient air temperature? Is your printer set up in a cold area or near an AC vent?
Re: Bed has stopped heating again
Nope. My printers have their own little room.
Re: Bed has stopped heating again
The replacement cost for a rambo mini is $120 or you could reflash the arduino to turn on the heater bed signal using one of the pins available as shown in the diagram labeled 'exp 2' or 'p3'. You would hook this pin to relay (SPDT 15 Amp CONTACTS 12V DC CONTROL RELAYS), SSR, or Mosfet. If using a SPDT relay make sure you add diodes to handle the EMF as to not fry the MCU. If you go the SSR route, read this thread: http://forum.seemecnc.com/viewtopic.php?t=9760 .
If you do not want reflash, you could also wire in the 3d bed mosfet circuit tapping in right before r56 or r57 which is right near the 15 amp fuse: https://www.amazon.com/gp/product/B01HCVJ3K2/ref=pd_sbs_328_1?ie=UTF8&psc=1&refRID=ZSXQBY0S324A0CZ3H1Q5
Check for a 5v signal at r56 or r57 with the multimeter to make sure everything else is working properly.
