V2 board starts burning when attempting dfu mode

[boannarrow]

My monster8 v2 starts burning on the marked piece after holding the boot button while the board is off and turning it on with the button pressed. I'm trying to add marlin binary file transfer via octoprint. Marlin 2.1-bugfix. My ras-pi and my computer see my board as a com port but the .bat files don't run and dfu-utils isn't recognizing my device.

[MKS-hosiey]

you can copy the mks_monster8.bin file to the TF card, and you can update it with the card, or update the .bin file through dfu

[HattonLe]

I confirm this "V2 board burning" issue - When you put the Monster8 board into DFU mode the bed heater MOSFET Q7 is enabled (the red LED turns on), and the printer bed heats up. It does this because the HOTBED signal comes from PB10, which happens to be UART3 TX which can be used for DFU communications by the bootloader. When idle UART3 TX sits at a HIGH state (3.3v).
The resultant smoke and a smell of burning from my Monster8 circuit board was not a good sign. Upon investigation I see that the MOSFET Q7 got so hot it has almost melted itself off the circuit board. Looking into the Q7 drive circuitry R40 was measuring 100 Ohms (should be 100k). This indicated the MOSFET was destroyed.

I was using a 12 VDC silicone heater which took 14 Amps, so approx 169 Watts. According to the MOSFET datasheet it should have been fine with this amount of load.

I am waiting for a response from MKS technical support regarding this issue.

[HattonLe]

In the end I think Q7 MOSFET was a faulty component from manufacturer. Not good ;O(
Got naff all help from the Monster8 supplier so I repair the board myself by replacing Q7 MOSFET with a equivalent one and also changed MOSFET drive signal from PB10 to PA8. This just needed removing of the 100Ohm SMD resistor situated near the external drive jumper.
I'm going to be using a 240VAC mains powered bed heater anyway which is way more efficient and this will take the strain off the bed heater circuitry - using high power MOSFETs for this application isn't a good idea.

Anyway the repair is working and entering DFU mode doesn't cause problems any more.

[FauthD]

+1 here.

[FauthD]

Well, I do not think this is a faulty Q7 device. Too much coincidence for this many cases. All after using DFU with 24V connected.

For Q7 the situation in DFU is the same as in normal bed heating (if 3.3V is applied from the TX3).
Perhaps the ouput of TX3 (PB10) is much less (1.8V ?), leading to a partially switch on situation that heats up Q7 until it dies.

Just my guess after 50 years of experience in electronics.

[masapod2892]

Just encountered the same issue on the v1 board but in a different scenario. When I was heating the bed up to do my first print I smelled something burning then to my surprise the mosfet was hot enough to desolder itself.

I also did notice in dfu that mosfet is powered for some odd reason