Geeetech

I have a Geeetech Delta G2S.
I have been printing successfully for months. Had some problems with movement on the Z,X axis sorted that the bearings in top pulley`s had collapsed.
Printing was going well but I noticed that the smell of the pla was stronger than normal.Print finished and found that the heat bed was very hot. Checked the temp and found that it was well over the setting.
I have now found that as soon as the printer is switched on the bed heats up (Red led underneath is on) ignores the max temp setting.Ignores Repetier - Hosts manual control.
Any suggestions as to where the problem might be?
At the moment the I have disconnected the heat bed`s cables to stop it heating up. (The red led is on)
Thanks

There is a post about how to solve the problem of max temperature similar to your issue.
http://www.geeetech.com/forum/viewtopic ... 23&t=17030

Hi William
I have checked out the post. For Bed temp.
With thermister in it shows 21/0.
With thermister removed it shows 21/0 & err. MINTEMP Bed.
With jumper in its shows 0/0 Err MAXTEMP BED.

During this time the red led for the Bed is always on. Which tells me that power is being supplied to Heat the Bed.

What controls this? Pressing reset has not solved the problem.
It is a dual extruder model and I was wondering about using the 2nd extruder sockets for powering the bed/thermister.
Not sure about the power take on the extruders compared to the bed.
Any thoughts.

Sounds to me like one of the MOSFETs might have died.

If it's giving power constantly the MOSFET might be stuck, could there be a short on the board?

If the hardware has failed there's not much you can do unfortunately.

I do not know if there is a short on the board a visual check does not show any burn marks.
Everything else appears to be working ok. I am printing with pla on a cold bed at the moment and that is going fine.
I have been looking through the configuration.h settings and I see I can set the bed_maxtemp. So I shall see what happens when I set it to 50.
Also I was wondering if I could swap the bed power and thermister with extruder 2 inputs.

Set bed_maxtemp to 50. Connected bed, temp went up past 50 error come up Maxtemp_bed. Bed continued to get hotter.
Back to drawing board.

You are able to apply one of the extruder's power supplies to another extruder to examine the whether the issue continue.

Hi William
I have moved the bed power and its thermister to extruder 2. It works correctly (using extruder 2 slider in Repetier). This tells me thermister and heat bed are working correctly.
The problem must be with the electronics controlling the switching on and off for the heat bed. As I said before there is a red led which comes on when the heat bed is switched on. This is permanently on.
My knowledge of electronics is rather limited would I be correct in assuming that the Moset is the component that switches the bed on/off?

Yes you are correct, the MOSFET controls the power to the bed.

There are three of them on the board near the power connectors for the extruders and heat bed. Like I said before it sounds like one might have died on your board.

Another option could be that the digital pin driving the MOSFET has died.

If your running dual extruders you may need a new board or if your confident enough you could build a new MOSFET circuit on a separate board and use one of the spare PWM ports (I think one of the fan ports is capable of this) to drive it. This would require an update to the firmware though to use that port as the bed heater.

I hope this helps.

Most helpful wiccan2
I am only using one extruder at the moment. So for the time being I shall use those ports. I would like to alter the firmware to swap over the port allocation. Thus Repetier will show the bed temp under the bed control slider. Have not worked out where/what to alter in the firmwre at the moment.

What/where is the digital pin?
Visual inspection of the mosfet adjacent to the power socket shows the board as clean. Unable to see underneath at the moment.
I take it is possible to remove the mosfet and replace. Ithink my soldering skills are just up to it.