Heat Bed no longer functions RAMPS 1.4 I think my RAMPS board just bit the dust, with respect to the heat bead. It just stopped working. I took a multimeter to the connection posts on the RAMPS board to measure voltage when the bed is turned on, and get something like 0.3 VDC. Obviously dead. My extruder posts measure 11.4 VDC when the extruder is turned on. So it seems to be a component on the board that failed. Everything else seems to be functioning fine. Anybody know what to look at next or should I be looking for a new ramps board? https://reprap.org/forum/read.php?219,309103,309103#msg-309103 Mon, 09 Mar 2026 20:12:11 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?219,309103,650524#msg-650524 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,650524#msg-650524 ChaosReadman RAMPS Electronics Sun, 10 Apr 2016 05:54:34 -0400 https://reprap.org/forum/read.php?219,309103,603083#msg-603083 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,603083#msg-603083
I managed to get it working by using the bed output to activate a relay (it has enough power to switch the relay on and off). The relay feeds current directly from the power supply into the bed. I think it sounds like the MOSFET is toast.]]> JacquesD RAMPS Electronics Fri, 01 Jan 2016 04:09:41 -0500 https://reprap.org/forum/read.php?219,309103,602747#msg-602747 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,602747#msg-602747 o_lampe RAMPS Electronics Thu, 31 Dec 2015 03:39:14 -0500 https://reprap.org/forum/read.php?219,309103,602526#msg-602526 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,602526#msg-602526
I am have a similar problem (exact symptoms as above). I have done some investigations and am having trouble interpreting the results:

-There is no noticeable voltage drop across the fuses.
-When the bed in off (from repetier-Host) the voltage from the ground pin to both D8 terminals is 12 V
-When the bed is on the voltage is 0 V from the ground pins to both D8 pins.
-If I disconnect on one of the bed leads then the voltage to the one pin is 12 V and to the other is 0 V. Also there is a LED that lights up on the board. So something funny happens when it starts drawing current

Any help interpreting the finding would be greatly appreciated. Is it a bust fuse or MOSFET? Printer has worked fine for months before this

Thanks
Jacques]]> JacquesD RAMPS Electronics Wed, 30 Dec 2015 12:45:32 -0500 https://reprap.org/forum/read.php?219,309103,491456#msg-491456 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,491456#msg-491456 I had the same problem as you.. did you can fix your Hot Bed problem? Just want to know how is it going and how to attack it.]]> gatteen91 RAMPS Electronics Wed, 01 Apr 2015 13:15:48 -0400 https://reprap.org/forum/read.php?219,309103,310798#msg-310798 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,310798#msg-310798 MarkR RAMPS Electronics Fri, 14 Feb 2014 05:52:52 -0500 https://reprap.org/forum/read.php?219,309103,310023#msg-310023 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,310023#msg-310023 cat.farmer RAMPS Electronics Wed, 12 Feb 2014 12:45:37 -0500 https://reprap.org/forum/read.php?219,309103,309642#msg-309642 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309642#msg-309642
Quote
cat.farmer
I had a similar problem, mine was caused by the power connecter on the ramps. It melted itself to the point of no contact, but looked ok on the outside. So i would also check that there is power on the back side of the connector.

That's exactly what it looks like on mine...I looked very carefully at the power connector, and the side of it seems to have a blob of melted plastic. I wonder if this is a common problem?]]> congaree RAMPS Electronics Tue, 11 Feb 2014 16:38:04 -0500 https://reprap.org/forum/read.php?219,309103,309277#msg-309277 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309277#msg-309277 cat.farmer RAMPS Electronics Mon, 10 Feb 2014 22:17:11 -0500 https://reprap.org/forum/read.php?219,309103,309272#msg-309272 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309272#msg-309272 congaree RAMPS Electronics Mon, 10 Feb 2014 21:56:05 -0500 https://reprap.org/forum/read.php?219,309103,309257#msg-309257 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309257#msg-309257 During operation, you could check to see what voltage is on either side of the fuse, compared to Ground. It should be very close to the same. just be careful to only touch the lead of the fuse with the multimeter probe, and nothing else.
With the unit completely off and disconnected from the PSU, you could check the resistance of the fuse (from one side to the other). Make sure the PSU is disconnected, else you may get a wrong reading, or if it's still got some voltage, fry your meter.

With regards to the MOSFET, you really can't easily test it in-circuit. Eliminate all the other possibilities first. Once that's done, with RAMPS removed from the Arduino and no power, you "could" check the resistance between pairs of the 3 pins on the MOSFET. The main one to test is between the pin that goes to D8 from the MOSFET and Ground. That will only prove if the MOSFET has shorted out, but not if it's died open circuit.]]> Cefiar RAMPS Electronics Mon, 10 Feb 2014 20:47:31 -0500 https://reprap.org/forum/read.php?219,309103,309255#msg-309255 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309255#msg-309255
Thanks.]]> Evil Monkey RAMPS Electronics Mon, 10 Feb 2014 20:30:47 -0500 https://reprap.org/forum/read.php?219,309103,309254#msg-309254 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309254#msg-309254
Thank you so much for that thorough reply. A lot of very good information there.

I had nothing on my ramps actively cooled, so that is probably what ultimately did it in. I get nothing (well, 0.3 V, which is effectively zero) on D8.

So, I have some things to look at here...the fuse should have reset. BTW, this just happened out of the blue...has been working fine for about 8 months until this happened.

Thank you again!]]> congaree RAMPS Electronics Mon, 10 Feb 2014 20:21:22 -0500 https://reprap.org/forum/read.php?219,309103,309242#msg-309242 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309242#msg-309242
That said, a lot of people have had issues with them.

They work internally by heat, so make sure that you have some airflow (doesn't need to be a lot - spill-over from a fan pointing at the stepper driver heatsinks is enough), and that they're not touching each other (the heat in one can trigger the other).

While the bed is turned on, measure the voltage from both pins on D8 compared to ground using a voltmeter (mutimeter on volts range - 20V max is fine). One pin should ALWAYS be 11+ VDC. If not, your fuse has most likely tripped, and something is drawing too much current.

If there is voltage there, then it's possible that the MOSFET is dead and needs replacing. The MOSFET for the bed can generate a lot of heat and needs to be actively cooled (heatsink on the MOSFET with a fan is best). If the MOSFET is dead, replace the stock MOSFET with an IRLB8743PBF (it's better than the stock component, and generates less heat). If you have trouble finding them, let me know where you're located and I'll see if I can find something similar from a local supplier for you.

Note: If the thermistor for the bed is disconnected, then the bed will NOT heat. This protection is in most firmwares, so you need to solve that first.]]> Cefiar RAMPS Electronics Mon, 10 Feb 2014 19:38:26 -0500 https://reprap.org/forum/read.php?219,309103,309204#msg-309204 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309204#msg-309204
Thanks for the quick response.

I checked both of the power inputs and both have 11+ VDC. I didn't realize these little boards had fuses on them. Are they those yellow square things? I don't see anything odd about them, but I've never seen fuses like that. 1) How do you tell if they are blown and 2) how do you change them if they are?

Thank you again.]]> congaree RAMPS Electronics Mon, 10 Feb 2014 17:40:23 -0500 https://reprap.org/forum/read.php?219,309103,309144#msg-309144 Re: Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309144#msg-309144 cdru RAMPS Electronics Mon, 10 Feb 2014 15:37:38 -0500 https://reprap.org/forum/read.php?219,309103,309103#msg-309103 Heat Bed no longer functions RAMPS 1.4 https://reprap.org/forum/read.php?219,309103,309103#msg-309103 congaree RAMPS Electronics Mon, 10 Feb 2014 14:33:50 -0500