<p>Considering:</p>

<blockquote>
  <p>Multimeter shows zero across the board's heat bed contacts</p>
</blockquote>

<p>this implies that </p>

<ul>
<li>If you measured <strong>resistance</strong>, the heated bed has no resistance. Basically this implies that the bed has a short. This might be the reason why it is not working. If you would power it as such you create a short. Instead of replacing the board, you need to replace the heated bed. Typical values for a heated bed of about 200&nbsp;x&nbsp;200&nbsp;mm are in the order of 1.2&nbsp;&Omega; (measurements between 0.9 and 1.5&nbsp;&Omega; are reasonable to be expected).</li>
<li>If you measured <strong>voltage</strong>, the heated bed does not receive power for heating, or the power does not reach the bed (not turned on or broken wire?). It would then be wise to measure the resistance (of the bed and the wires). If the resistance is in the order of about 1.2&nbsp;&Omega; (see above) for the bed, you could try to connect the heated bed directly to the PSU to see if it gets warm, if so, please disconnect immediately to prevent damage. From this experiment you can find whether the heated bed is broken (or the cables), or that the board is not functioning correctly, this is, however, strange as you tried 2 boards. A possible suspect could be the MOSFET that schedules the powering of the heated bed if you use an external MOSFET board that it.</li>
<li>If you measured <strong>current</strong>, then you found out that no power is delivered to the board, but you also might have broken your board in the process, as measuring current is a (close to) 0&nbsp;&Omega; connection and has to be done <em>in line</em> of a circuit.</li>
</ul>

CC BY-SA 4.0
2019-02-14T09:35:45.553Z
Perhaps the multimeter was in voltage measuring mode. The question doesn't say they were measuring resistance.
Tom van der Zanden
CC BY-SA 4.0
2019-02-14T10:05:30.610Z
@TomvanderZanden Good point! Updated the answer to include both.
0scar
CC BY-SA 4.0
2019-02-14T14:13:22.823Z
But it's unlikely the same MOSFET would be bad on both boards  (if the power MOSFET isn't on the board he replaced, then ignore this comment)
Carl Witthoft
CC BY-SA 4.0
2019-02-14T14:35:23.007Z
@CarlWitthoft The question does not state the use of an external MOSFET, good to make that clear
0scar
CC BY-SA 4.0
2019-02-14T19:13:03.040Z
1: The MKS GenL is a purpose-built board, nothing external. 

2: With the bed (supposedly) heating (issued M140 S60, response OK), I measured DC voltage on the board's heated bed connector, as shown in this image: postimg.cc/jD5Sbhtj
Bill in Kansas City
CC BY-SA 4.0
2019-02-14T19:41:38.587Z
More info: put 12V to the bed and it began heating. Multimeter on 200Ω measured .5. Anything higher than that was zero.
Bill in Kansas City
CC BY-SA 4.0
2019-02-13T20:07:03.870Z
2019-02-14T16:44:31.460Z
2019-02-14T16:44:31.460Z
0scar
<p>Since the bed was warm when you connected to 12 V that means the bed and the wiring are good. It sounds like your multimeter is not too accurate, with a reading of 0.5 Ω (or you measured accidentally some other circuit), but no worries. </p>

<p>Since both boards do not power the bed, it seems like it could be a firmware setting. To help with that, a look at your config file, and possibly the <code>pins_ramps.h</code> file can help.</p>

<p>As a first check, your <code>mks_gen_L.h</code> file should look like this;</p>

<pre><code>    #if HOTENDS &gt; 2 || E_STEPPERS &gt; 2
  #error "MKS GEN L supports up to 2 hotends / E-steppers. Comment out this line to continue."
#endif

#define BOARD_NAME "MKS GEN L"

//
// Heaters / Fans
//
// Power outputs EFBF or EFBE
#define MOSFET_D_PIN 7

//
// CS Pins wired to avoid conflict with the LCD
// See https://www.thingiverse.com/asset:66604
//

#ifndef X_CS_PIN
  #define X_CS_PIN 59
#endif

#ifndef Y_CS_PIN
  #define Y_CS_PIN 63
#endif

#include "pins_RAMPS.h"
</code></pre>

<p>Now all you need to confirm is that your bed is hooked to D7.</p>

CC BY-SA 4.0
2019-02-26T14:11:48.890Z
the main part is good, but I have experienced a lot of people just having problems how to measure the resistance correctly.
Trish
CC BY-SA 4.0
2019-02-26T16:23:18.593Z
@yellow I'm grateful for the firmware comment: when I upgrade to the latest version of Marlin (in about a week when I get new stepper drivers; I'm going to do everything at once) I may well have to know that. However, the original board WAS powering the bed, and then stopped; I can see on the board where the connection failed. At the time it was still running the original firmware, and no other changes had been made.
Bill in Kansas City
CC BY-SA 4.0
2019-02-26T16:23:51.293Z
@Trish This is quite likely. I'm currently attending the University of Google, and the class content isn't always clear. "A Beginner's Guide To..." articles are rarely vetted by actual beginners.
Bill in Kansas City
CC BY-SA 4.0
2019-02-26T16:59:37.447Z
@BillinKansasCity how about having a talk about that in [chat]?
Trish
CC BY-SA 4.0
2019-02-26T20:22:18.197Z
@Trish At your convenience. I'm back at my desk and available.
Bill in Kansas City
CC BY-SA 4.0
2019-02-26T12:32:41.240Z
2019-02-26T14:11:11.113Z
2019-02-26T14:11:11.113Z
yellow
<p>Flsun 3D Cube; Marlin 1.1.1; main board: Makerbase MKS Gen_L V1.0; running from either Repetier or OctoPrint.</p>

<p>I was recently obliged to replace the main board when it stopped powering the heated bed. I got the new main board - same make, version, etc - got everything setup just as it was before, but the bed still doesn't heat. Multimeter shows zero across the board's heat bed contacts, whether using G-code from the terminal (in both Repetier and Octoprint), G-code in the print file, or the control panel on the front of the printer. The thermistor works: if I shine a heat lamp on the bed, it registers the temp change.</p>

<p>Bad board? Something in the Merlin config I missed? Is the board smart enough to not power it on if the bed heater itself is bad?</p>

CC BY-SA 4.0
2019-02-13T17:52:04.633Z
Welcome to 3dPrinting.SE! You state "Marlin 1.1.1" ... is that correct? Marlin [1.1.9](http://marlinfw.org/meta/download/) is the most current stable version. You might try loading it and seeing if the issue still exists.
Pᴀᴜʟsᴛᴇʀ2
CC BY-SA 4.0
2019-02-14T14:13:34.360Z
One of the prime rules of problem-solving: don't assume a cause.  In this case, that means don't replace a board until you know it is actually the reason you're not heating.
Carl Witthoft
CC BY-SA 4.0
2019-02-14T14:14:23.980Z
Do any other outputs (e.g. xyz drives) work?
Carl Witthoft
CC BY-SA 4.0
2019-02-14T19:15:55.387Z
@CarlWitthoft 1. Good advice for any situation. Not replacing the board (in other words: spending more money) until I'm sure.

2. All other outputs work: the printer functions normally otherwise. My prints are curling on the corners, so I am motivated to fix the bed.
Bill in Kansas City
CC BY-SA 4.0
2021-01-21T19:37:27.287Z
have you solve Your problem? I have the same issue with bed heating in the same printer. Everything works great till today. When I set up heating the LED on board turn on, but I don't have any voltage on pins.
Kamil Kozieja
CC BY-SA 4.0
2021-01-22T23:28:06.603Z
I solved it by switching to an MKS GEN L v1.4 with an external mosfet. The MKS boards just don't have the oomph to drive a heated bed for any length of time.
Bill in Kansas City
<electronics><flsun-3d-cube>
Main board heated bed connectors aren't powering up
Bill in Kansas City
# Main board heated bed connectors aren't powering up

(Asked by: username_0 on 2019-02-13)

Flsun 3D Cube; Marlin 1.1.1; main board: Makerbase MKS Gen\_L V1.0; running from either Repetier or OctoPrint.

I was recently obliged to replace the main board when it stopped powering the heated bed. I got the new main board - same make, version, etc - got everything setup just as it was before, but the bed still doesn't heat. Multimeter shows zero across the board's heat bed contacts, whether using G-code from the terminal (in both Repetier and Octoprint), G-code in the print file, or the control panel on the front of the printer. The thermistor works: if I shine a heat lamp on the bed, it registers the temp change.

Bad board? Something in the Merlin config I missed? Is the board smart enough to not power it on if the bed heater itself is bad?

**Tags:** electronics, flsun-3d-cube

> **Comments:**
> **username_1**: Welcome to 3dPrinting.SE! You state "Marlin 1.1.1" ... is that correct? Marlin [1.1.9](http://marlinfw.org/meta/download/) is the most current stable version. You might try loading it and seeing if the issue still exists.  
> **username_2**: One of the prime rules of problem-solving: don't assume a cause.  In this case, that means don't replace a board until you know it is actually the reason you're not heating.  
> **username_2**: Do any other outputs (e.g. xyz drives) work?  
> **username_0**: @username_2 1. Good advice for any situation. Not replacing the board (in other words: spending more money) until I'm sure.  2. All other outputs work: the printer functions normally otherwise. My prints are curling on the corners, so I am motivated to fix the bed.  
> **username_3**: have you solve Your problem? I have the same issue with bed heating in the same printer. Everything works great till today. When I set up heating the LED on board turn on, but I don't have any voltage on pins.  
> **username_0**: I solved it by switching to an MKS GEN L v1.4 with an external mosfet. The MKS boards just don't have the oomph to drive a heated bed for any length of time.  

---

## 2 answers

### Answer by username_4 on 2019-02-13. Score: 2

Considering:

> Multimeter shows zero across the board's heat bed contacts

this implies that

* If you measured **resistance**, the heated bed has no resistance. Basically this implies that the bed has a short. This might be the reason why it is not working. If you would power it as such you create a short. Instead of replacing the board, you need to replace the heated bed. Typical values for a heated bed of about 200 x 200 mm are in the order of 1.2 Ω (measurements between 0.9 and 1.5 Ω are reasonable to be expected).
* If you measured **voltage**, the heated bed does not receive power for heating, or the power does not reach the bed (not turned on or broken wire?). It would then be wise to measure the resistance (of the bed and the wires). If the resistance is in the order of about 1.2 Ω (see above) for the bed, you could try to connect the heated bed directly to the PSU to see if it gets warm, if so, please disconnect immediately to prevent damage. From this experiment you can find whether the heated bed is broken (or the cables), or that the board is not functioning correctly, this is, however, strange as you tried 2 boards. A possible suspect could be the MOSFET that schedules the powering of the heated bed if you use an external MOSFET board that it.
* If you measured **current**, then you found out that no power is delivered to the board, but you also might have broken your board in the process, as measuring current is a (close to) 0 Ω connection and has to be done *in line* of a circuit.

> **Comments:**
> **username_5**: Perhaps the multimeter was in voltage measuring mode. The question doesn't say they were measuring resistance.  
> **username_4**: @username_5 Good point! Updated the answer to include both.  
> **username_2**: But it's unlikely the same MOSFET would be bad on both boards  (if the power MOSFET isn't on the board he replaced, then ignore this comment)  
> **username_4**: @username_2 The question does not state the use of an external MOSFET, good to make that clear  
> **username_0**: 1: The MKS GenL is a purpose-built board, nothing external.   2: With the bed (supposedly) heating (issued M140 S60, response OK), I measured DC voltage on the board's heated bed connector, as shown in this image: postimg.cc/jD5Sbhtj  
> **username_0**: More info: put 12V to the bed and it began heating. Multimeter on 200Ω measured .5. Anything higher than that was zero.  

---

### Answer by username_6 on 2019-02-26. Score: 0

Since the bed was warm when you connected to 12 V that means the bed and the wiring are good. It sounds like your multimeter is not too accurate, with a reading of 0.5 Ω (or you measured accidentally some other circuit), but no worries.

Since both boards do not power the bed, it seems like it could be a firmware setting. To help with that, a look at your config file, and possibly the `pins_ramps.h` file can help.

As a first check, your `mks_gen_L.h` file should look like this;

```
    #if HOTENDS > 2 || E_STEPPERS > 2
  #error "MKS GEN L supports up to 2 hotends / E-steppers. Comment out this line to continue."
#endif

#define BOARD_NAME "MKS GEN L"

//
// Heaters / Fans
//
// Power outputs EFBF or EFBE
#define MOSFET_D_PIN 7

//
// CS Pins wired to avoid conflict with the LCD
// See https://www.thingiverse.com/asset:66604
//

#ifndef X_CS_PIN
  #define X_CS_PIN 59
#endif

#ifndef Y_CS_PIN
  #define Y_CS_PIN 63
#endif

#include "pins_RAMPS.h"

```

Now all you need to confirm is that your bed is hooked to D7.

> **Comments:**
> **username_7**: the main part is good, but I have experienced a lot of people just having problems how to measure the resistance correctly.  
> **username_0**: @username_6 I'm grateful for the firmware comment: when I upgrade to the latest version of Marlin (in about a week when I get new stepper drivers; I'm going to do everything at once) I may well have to know that. However, the original board WAS powering the bed, and then stopped; I can see on the board where the connection failed. At the time it was still running the original firmware, and no other changes had been made.  
> **username_0**: @username_7 This is quite likely. I'm currently attending the University of Google, and the class content isn't always clear. "A Beginner's Guide To..." articles are rarely vetted by actual beginners.  
> **username_7**: @username_0 how about having a talk about that in [chat]?  
> **username_0**: @username_7 At your convenience. I'm back at my desk and available.  

---

