K8400 heaters on uncontrollably (thermal runaway)

Vertex 3D Printer Vertex - Issues while printing
1

Hi everyone!

During the replacing of one of two damaged printheads on my K8400 I must have shorted something as all of a sudden the heaters started heating up uncontrollably (like a thermal runaway). Whenever the printer is powered the red lights on the printhead come on and it heats up, up until the point where everything starts smoking (ignoring the MAXTEMP 275C warning).
I have the feeling either the mainboard (VM8400MB) the individual drivers are broken (VM8400DB?).

Things I have tried:

• Using different extruder board (P8400EXTED) but on this one the two red LED’s also light up
• Unplugging drivers on the mainboard, same result
• Reflashing firmware. It performed this without problems however the uncontrollable heaters remain. I can also still control the printer like normal. Just the heaters are uncontrollable.

I have ordered a new VM8400MB and 2x VM8400DB to be sure. I am not sure these control the heaters as well or whether it is just the stepper motors. All stepper motors work fine

Does someone know what exactly is broken if the heaters are constantly on?

Any advice in what order I should replace the mainboard?

2

The VM8400DBs are not to blame since these just control the motors.
Sound like you need to just replace the VM8400MB.
When changing the firmware make sure the printer is not plugged in.
This can cause the heaters to turn on while the firmware upload is happening

3

[quote=“Wrong Way”]The VM8400DBs are not to blame since these just control the motors.
Sound like you need to just replace the VM8400MB.
When changing the firmware make sure the printer is not plugged in.
This can cause the heaters to turn on while the firmware upload is happening[/quote]

Perfect, thank you. As soon as I get the new VM8400MB I will come back and post results.

4

Did you check the supply voltage output of the power supply? A significant over-voltage on this part can also generate such effect.

5

The power supply is 15.1 DC which I thought was high. I connected it all to a clean 12V power supply but same results; both heaters still are on, uncontrollably.

Edit PSU apparently should be 15V.

6

A new mainboard (VM8400MB) solved the issue!! Everything working normal again!

Thanks for your input!

7

Glad to hear it’s up and running again.
Enjoy!

8

Is there another way to fix this without replacing the entire board? Some component that can be replaced on the existing board? Perhaps a blown transistor?

9

Not that I know of.