Heating failed ID: Bed. [Probably solved]

Hi reprap peoples,

Decided to get involved in the reprap scene and build a 3d printer, got everything going mostly sweet minus the MK2A heated pcb bed (200x200) which i can not just seem to get to work when connected via my Ramps 1.4 Board running marlin RC7. I have confirmed that the heatbed does work as i can plug it straight into the 12V 30A PSU and it heats up as well that the thermistor (https://www.aliexpress.com/item/5-pcs-lot-100K-ohm-NTC-3950-Thermistors-with-dupont-head-for-3D-Printer-Mend-Free/32360326755.html?spm=2114.13010608.0.0.4YtxEy) also works as it was reporting the temperature change of the bed while plugged into the psu and the idle room temp. I have tried the same marlin build on another ramps board and received the same error so it makes me believe that most likely it is my config that is the issue.

It always results in this error reporting in repetier and on the LCD when trying to heat the heatbed, (the hotend D10, hotend fan D9 work fine fyi)
15:55:15.593 : Error:Heating failed, system stopped! Heater_ID: bed
15:55:15.597 : Errorrinter halted. kill() called!

Other possible thoughts is that it could be the manufacturer as both boards are from the same cheap chinese supplier? I probably should use a multimeter to check the voltage between the input and output but electronics is not my main forte so not sure which combo to use or setting on the multimeter to not cause it to short circuit.

Any help would be most appreciated as I have been stumped by this for the last 4 days, about to try a couple options with the thermal runaway protection turned off but the mere idea seems like a poor option/solution.


Cheers

Edited 1 time(s). Last edit at 10/20/2016 07:52AM by VooDoo.maGiK.

You do have both the 5amp and the 11 amp circuits plugged in? (ie 4 wires, two 12v and 2 gnds, into the 4 pin power plug) It always pays to check the obvious...


Put a multimeter into both pins of D8, turn on the bed in software, do you get 12v?

Also try the heated bed with the bed +12v plugged into D8 + but the gnd directly to gnd on the power supply.. This is un controlled heating, but lets you test the entire 11amp cct, threw screw connectors, and fuse, but bypasses the mosfet (on the gnd wire)

also try removing the ramps, load up the led flashing demo sketch and change it to pin 8, check you get 5v on D8 pin when its on.. this tests the mega.

but its most likely the mosfet is dead. they are not very well suited for this job and are easily damaged by static
replace with a IRLB 8743

Edited 3 time(s). Last edit at 10/20/2016 04:17AM by Dust.

I just cringed, some times the obvious is the first thing you miss, will hang my head in shame and confirm tomorrow arvo that i am in fact a idiot when i wire in the second 12v + gnd cable

many thanks to you Dust for your wealth of other knowledge and advice will not go to waste as it helps me think and understand how to diagnose any likely future problems i encounter/make so many thanks for excellent post normally one must go digging very deep to find such information (which previous huntings for some one in a similar situation could not find which now makes sense as well)

cheers