Geeetech Prusa I3 Pro B problem with heatbed

[Anehall]

Hi!

I have used my printer for several months now but yesterday when i was starting the printer the bed started heating up on its own?

In repetier it says that bed/nozzle are turned off but the bed temp wont stop rising... it reaches over 100C and i have to cut the power to the printer to stop it rising...

Reinstalled my firmware now and are out of ideas because it didnt work...

Thanks for the help

Fredrik

[William]

Hi!

I have used my printer for several months now but yesterday when i was starting the printer the bed started heating up on its own?

In repetier it says that bed/nozzle are turned off but the bed temp wont stop rising... it reaches over 100C and i have to cut the power to the printer to stop it rising...

Reinstalled my firmware now and are out of ideas because it didnt work...

Thanks for the help

Fredrik

Hi,
Maybe the heatbed mosfet caused it.The mosfet controls the bed to heat up or not.So you'd better check if it is bad.
Refer to this:http://www.geeetech.com/forum/viewtopic ... 19&t=17039

[Anehall]

Hi again!

Looks like the mosfet is burned. Look at the photo. What do I do now? Do i have to change the board or can i just replace the mosfet?

[William]

Hi again!

Looks like the mosfet is burned. Look at the photo. What do I do now? Do i have to change the board or can i just replace the mosfet?

Hi,
Actually,you don't need to change the board cuz everything is OK except the heatbed.And you can replace the bad mosfet with the one neighbours the extruder 2,cuz the extruder2 is not in use.
Let me know plz how it goes after you have done that.
Regards

[Anehall]

Hi again

Changed the mosfet from extruder 2 to my heatbed... now the heatbed wont heat up anymore and the extruder cant heat up over 197C... so i didnt work. Ordered a new board... Is there a way to protect the mosfets so i dont happen again?

[William]

Hi again

Changed the mosfet from extruder 2 to my heatbed... now the heatbed wont heat up anymore and the extruder cant heat up over 197C... so i didnt work. Ordered a new board... Is there a way to protect the mosfets so i dont happen again?

Hi,
Except the heat sink,the codes will help to protect the mos from overheating:
//#define HEATER_BED_DUTY_CYCLE_DIVIDER 4
Increase the value "4" will work,but it will take a bit longer time to reach the target temp.

[searider19]

Hi,

maybe some find useful tips from my story around extruder heating on Prusa I3 Pro B. At first turn on of printer, extruder turned on and go to 280°C (PTFE tube was damaged). Ok many suggested that check for MOSFET, but the mosfet was OK. I take another mosfet but extruder turned on on power on. So I figured out the problem was bad GT2560 board production around mosfets (bad lacquer protection). Small unprotected area under heatsink caused short between heatsink(mosfet TAB in this case it's DRAIN and it means 12V) and G-line passing directly under heatsink. So I had always open mosfet because of this short. This was the cause of my problems and maybe others have same problems but never pay attention to that. I think that this unprotected area a result of mounting heatsink to board (heatsinks have a very sharp edges). So I protected G-line simple with cd/dvd marker (use something not conducting) and I also remove lower edges of heatsinks, that G-line isn't anymore directly under heatsink. Another thing what I did was to remove original mosfets with better one, so now under full load the mosfets are cool.
I printed for 1 mont without problems and now another problem appeared (Y-axis misaligment).


Best regards.

[Anehall]

Hi again...

Changed the mainboard and now it works... Was the burnt mosfet... thank you!