Geeetech A10 GT2560 v3 - Bed temp at 124/125/126/127 degrees... when cold

[simonemery555]

i have just checked the beds thermistor and it is working fine.

any help would be greatly appreciated

[simonemery555]

Shorted out the thermistor, and the temp jumps to 358 as it should, but drops back to 125.

Seems like it’s software eprom failure/or another chip/transistor failing to report logical readings

Help!

[TMeeks]

While our specific issues are a bit different, they are enough alike to work together to find resolution.

http://www.geeetech.com/forum/viewtopic ... 98&t=62327

Fortunately, we have a second unboxed A10 which we can raid for parts until we identify which part is the culprit. Our plan is to swap the following parts in order to see which new part solves the issue.

• Heated Bed
  GT2560 V3.0
  Wiring harness for the bed.

I will also be following your progress.

[simonemery555]

Perhaps similar, but mine has to be the control board, and I feel the actual eprom has failed.

Its stuck on 124-127 degrees and fails to actually heat no matter what I’ve tried:

Any version of Marlin, restore failesafes save clean setting etc.
Headless (without the LCD ribbon plugged in).
Without the bed main connector plugged in to control bord.
Without the extruder main connector plugged in to control board.

Unplugging the beds main connector should indicate -14 degrees, but on mine it does not. I think your problem is the wiring loom. They are notorious for wires or connectors splitting or dry joints in the connectors, and would explain why you are getting -14 randomly as it looks to be getting unplugged, or as it tries to heat, the is causing expansion and a connection is getting broken. Check the blue and green wires for continuity from your solder points on your bed to the end of the cable plug and wiggle them as you do. Or even better, from the thermistor solder joints under the insulation pad taped to the underside.

[simonemery555]

photos for clarity:

https://photos.app.goo.gl/iPz82tJomfD8PN9r5

[simonemery555]

Anyone any ideas?

[_kaktus_]

Hello


if possible, try switching the measurement input (ADC in) to the one that is not currently in use. This will be a very good test and will rule out the problem of a defective measuring input

In order to do this, you need to change the configuration of the pins and upload the firmware anew

[simonemery555]

Thanks for the reply, but are you able to give a little more detailed info please?

[_kaktus_]

Hi.


If this is not a problem for you, attach a file with the definition of µC leads to the message.
I will look at it in my free time.
I don't like Arduino environment and all the confusion around Marlin firmware ... well, but well ...

We will be interested in µC outputs, which have analog-to-digital converter functionality.
We have to check which of them are not used in the controller circuit.
.

pinout-ATMega2560_ADC.png (125.95 KiB) Viewed 8919 times

.
Unfortunately, the published circuit diagram of the controller board does not seem to be consistent in the PCB.

From one of the users of the forum (it's a pity not from the GT Team) I have a photograph of excellent quality:
.

GT2560_v3_ADC.jpg (351.08 KiB) Viewed 8919 times

.
I don't remember from whom I have this photo, but thank you beautifully, and I hope I can share it here.
You can see on it goldpin signed ADC.

Our task is to assign a new pin the necessary functionality, and a small modification of the PCB mosaic.

[simonemery555]

hmmm thanks, but i think think this is far beyond my skill set. I got it as a Christmas present so only know the basics.

Am i right in thinking that this is not normal at all? I've been searching the forums and no one else seems to of had the same issue.