Bed Heater Not Heating

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Possible causes (if other parts, particularly the hot end, are working):

1. Your gcode isn't telling the bed heater to heat up: IAP's Cura video says to uncheck the "heated bed" option; this is incorrect. If left unchecked Cura will generate gcode that will NOT heat the bed regardless of having set a temperature. If you have the LCD and notice ##/0 or if you don't have the LCD and have "heated bed" unchecked in Cura, try checking it. If you have the LCD, you should see a "##/##" reading... to start, it'll probably read as like "24/0" as the ambient room temperature is the left number or "current temp" and the right number, the target temp, is zero. Once you start printing or if you use the LCD to tell it to pre-heat, it should read something like "24/70" and the 24 will rise as it heats up. If you see a target temp and it's still not heating, then it's time to look at the next few things. And, obviously, make sure you have a temperature set before generating the gcode.

2. Damaged PCB: Some people have received bed heater PCBs that were damaged. This was generally visible damage to the PCB which severed circuit traces so there was no electrical flow to create heat. Check for scratches on the PCB. If you have a multimeter, check the resistance between the bed heater's contacts (it should be very low).

3. Thermistor faulty or missing: The PCB has a thermistor just like the hot end has (but in a different package). If that's not working properly, the firmware, for safety reasons, will not allow the bed to be heated since it can't tell how hot things are. The thermistor should be near the center of the bed.

If the thermistor is faulty, it can be replaced. Desolder the faulty thermistor from R1, and solder in a replacement. You should use a soldering iron/station with temperature control, as most SMD thermistors are only heat tolerant to 260C but can withstand a bit above this when using an iron. Up to 300-350C should be okay, just do not leave the iron on the pads or contacts for more than a second at a time.

It is currently unknown what the OEM thermistor used on the Rigidbot is, but the Vishay BC Components NTCS0603E3104FXT is an easily available replacement from digikey (http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=173220666) , mouser (http://www.mouser.com/ProductDetail/Vishay-BC-Components/NTCS0603E3104FXT/?qs=sGAEpiMZZMuBd0%252bwiCVS24o8envvpdBo10p3l8T73t0%3d) and others.

Two changes are necessary in firmware to configure the Vishay thermistor.

In configuration.h, look for TEMP_SENSOR_BED and change it from the default value to 8

 #define TEMP_SENSOR_BED 8

In thermistortables.h, look for the #if statement below and replace the table values with the ones below (credit to http://etherpod.org/blog/?page_id=7886 for doing the work to calculate the real measured value table)

 #if (THERMISTORHEATER_0 == 8) || (THERMISTORHEATER_1 == 8) || (THERMISTORHEATER_2 == 8) || (THERMISTORBED == 8)
 // 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup)
 const short temptable_8[][2] PROGMEM = {
    {1*OVERSAMPLENR, 816},
    {36*OVERSAMPLENR, 282},
    {71*OVERSAMPLENR, 233},
    {106*OVERSAMPLENR, 207},
    {141*OVERSAMPLENR, 189},
    {176*OVERSAMPLENR, 176},
    {211*OVERSAMPLENR, 165},
    {246*OVERSAMPLENR, 156},
    {281*OVERSAMPLENR, 148},
    {316*OVERSAMPLENR, 141},
    {351*OVERSAMPLENR, 135},
    {386*OVERSAMPLENR, 129},
    {421*OVERSAMPLENR, 123},
    {456*OVERSAMPLENR, 118},
    {491*OVERSAMPLENR, 113},
    {526*OVERSAMPLENR, 108},
    {561*OVERSAMPLENR, 103},
    {596*OVERSAMPLENR, 98},
    {631*OVERSAMPLENR, 93},
    {666*OVERSAMPLENR, 89},
    {701*OVERSAMPLENR, 84},
    {736*OVERSAMPLENR, 79},
    {771*OVERSAMPLENR, 74},
    {806*OVERSAMPLENR, 68},
    {841*OVERSAMPLENR, 62},
    {876*OVERSAMPLENR, 55},
    {911*OVERSAMPLENR, 47},
    {946*OVERSAMPLENR, 37},
    {981*OVERSAMPLENR, 23},
    {1016*OVERSAMPLENR, 0}
 };
 #endif

4. Bad cable or connector: Check your bed heater cable and connectors. Several bad cables have been reported. Ensure cables are plugged in tightly on both ends. Using a multimeter to check for continuity would be more definitive that visual inspection.

5. Main board failure: The last resort is a main board problem. If you are not experienced in circuit board repair, it's probably best to request a replacement part.

Board with missing thermistor and scratch
Board with missing LED and resistor (this won't impair function)