Heatbed won't heat, LED2 off

Wondering if there's a procedure to troubleshooting a RAMPS 1.4 that won't heat the bed. LED 2 is off, voltage at D8 is 0. My only idea is to get a new RAMPS, which is not optimal if there are alternatives. Are there?

Voltage at d8 may be a clue...


If you measure voltage from d8 + to power plug negative it should measure supply voltage. This is always connected. The mosfet connects the - line of D8

If its missing you either don't have the 12v 11amp plugged in, or turned on, or the 11amp polyfuse is dead.

You can also plug the heated bed into D8 + and -v on power supply to test it (It will uncontrollably heat up, so you cant leave it this way )

Edited 2 time(s). Last edit at 06/27/2016 08:17PM by Dust.

Ok, I don't know how I measured it the first time, now I'm reading supply voltage at both D8+ and D8-.

Still, the D8- refuses to go to ground, which means I have a malfunction somewhere. Btw my 11A polyfuse is gone, I jumpered across it so it's not a factor.

I did test the heated bed before: it heats properly, so this is a RAMPS issue, just not sure how to fix it.

The D8 mosfet is probably dead, replace it, preferably with a better mosfet eg a IRLB 8743

The mosfet is directly connected to the D8 I/O line of the mega... so its either the mosfet or the mega

It could also be firmware, if you have never had it working (must have motherboard set to a ramps )

Don't think it's firmware, I've had the hotend working no problem, and the motherboard is defined as BOARD_RAMPS_13_EFB.

Ok, I'll try replacing the Mega first (I've got a spare) and then the MOSFET. Only downside is I'll have to wait a while for the new FET.

Update: my spare mega seems busted, so it's time for a long timeout while parts arrive... Thanks for the help.

Edited 1 time(s). Last edit at 06/27/2016 10:44PM by anvoice.

in the mean time you could setup a led and a resistor and plug it into d8 on the mega, then load the demo blink program and change that to use d8 also.. would show you if that pin is dead.

See here [www.arduino.cc]

Thanks, I managed to find another spare Mega. Looks like it's the RAMPS after all.

Edited 1 time(s). Last edit at 06/28/2016 05:15PM by anvoice.

Time for an embarrassing confession. It was #define TEMP_SENSOR_BED 0. No idea how it wound up that way, as I was carrying over settings from a Prusa i3 with a heated bed. Bed now heats properly, and I've got a spare RAMPS coming in the mail. All's good that ends well. Time to try some PETG prints, if they stick to my Kapton.

Edited 2 time(s). Last edit at 06/29/2016 12:14AM by anvoice.