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Broken Thermistor killing the GT2560 V3.0 board

Posted: Sat May 04, 2019 5:47 am
by caesar_1111
Now for the second time :oops: a broken thermistor on the extruder killed my GT2560 V3.0 board!
The board now only shows some fixed temperatures.
Is the board should not break if only a thermistor is breaking and since it is now the second time, I wonder if other users are also experiencing this issue? :?: :?:
Or is something wrong with other components like the wiring and I have to replace the printer completely.
Also if anyone knows which element on the pcd does the processing of the thermistor values. :?: :?: :?:
I already tried the resistors but with no effect....

Re: Broken Thermistor killing the GT2560 V3.0 board

Posted: Sat May 11, 2019 8:45 am
by caesar_1111

after a few days root cause analysis I found the reason:
At some heater cartridges the wire insulation is not firm, moving to far and revealing the bare wire.
If this wire touches the hotend, 24V voltage is applied to the hotend even when the extruder is not heating.
No if the thermistor breaks like the glass pearl is breaking and revealing the wires and those wires are touching the hotend, you will have the 24V voltage no on the thermistor line T0 wich is directly linked to the T0 pin of the ATMEGA2560 chip on the board. This most likely is killing the measuring capability of at least the T0 pin which will result in crazy temp reading on the display.

So better take precautions:
Every time your are doing something with the hotend it is recommended to check if the heater cartridge or the thermistor is touching the metal parts of the hotend.
REASON: If both the cartridge wire an the thermistor wire it touching the metal, you instantly fry the mainboard!
Just unplug the cartridge and thermsitor plugs on the extension board, use a multimeter in diode mode and check the metal hotend vs. every line of the wiring.
Heater cartridge: The heater cartridge wires need to be bent 90 degree so make sure your heater cartridge is at least even or about 1mm outside the heatend. Best is if you also turn the cartridge vertically, so the little piece of wire exposed has enough clearance to the hotend. Advanced: you can also get yourself some hight temp silicone (+350°C e.g. K2 bond black silicone) or even exhaust assembly paste (+1000°C e.g. holts firegum but this will not be flexible) to seal the bare wires. this stuff might also help you with some hotend sealing...
Use a PTFE washer for the screw pushing the thermistor into the hotend. You might get the same result with a PTFE plumbing tape wrapper around the screw and the thermistor wires. Also possible is to use the high temp silicon, to just glue the thermistor into place, but this is somehow permanent.

Currently Geeetech is looking into the problem and trying to find an improvement and maybe a silicon sock will help in insulation the hotend.

Meanwhile I am waiting for some replacement ATMEGA2560 chisp trying to just resolder the new ones to the old board. If this is successful, you might have a cheaper solution than replacing the whole board.
I will keep you posted.

BTW: for further tips you can always check out:

Re: Broken Thermistor killing the GT2560 V3.0 board

Posted: Sat May 11, 2019 6:18 pm
by _kaktus_

I was going to help you solve this problem, but I didn't make it in time. :roll:

But you did a great job on your own. My congratulations.

I've prepared a snippet from the schematic for you. So I put it here.
GT2560_V3.0_Temperature_sensor.jpg (19.58 KiB) Viewed 1428 times

If you feel strong you can change the ADC µC input, and you don't need to solder a new chip.

Re: Broken Thermistor killing the GT2560 V3.0 board

Posted: Sun May 12, 2019 11:00 pm
by caesar_1111

thks for the solution, but since I managed to fry 2 boards.... the one board your solution might help, but on one board frying the chip did not only throw off the T0 readings but grounded T1, so I have a permanent -14°Celsius :)

Ah and nice that you are showing the shematics....
they are worng as well!
the mixed up the T0 and T2 number on the current PDF at their homepage.
You you will defenitly change the wrong capacitor if you use the shematics numbers....;)

...anyway, I got myself a backup board since I now run 2 A10M and I like to have one spare. Geeetech meanwhile is sending me replacement for the fried board.

And I will post a design for a improved hotend silicone sock, as soon as I get my silicone an was able to poor one and test it.


Re: Broken Thermistor killing the GT2560 V3.0 board

Posted: Mon May 13, 2019 12:39 am
by _kaktus_

Full schematics are available on the forum.
Search in the appropriate section. ;)

Re: Broken Thermistor killing the GT2560 V3.0 board

Posted: Mon May 13, 2019 1:44 am
by _kaktus_

Oh, and one more thing:

This version of the controller board has all ADC inputs routed to the goldpin connectors.
So you can successfully try to restore your controllers. If of course you are not afraid to modify the PCB.

Re: Broken Thermistor killing the GT2560 V3.0 board

Posted: Fri May 17, 2019 6:55 am
by caesar_1111
@ _kaktus_: I used the official link of geeetech: which contains the full shematics.... but with the mixed T0 T2 numbers.....

and here we go with the physical solutions:
I designed a mold for a silicone sock wich will insulate the thermistor and heater cartridge wires.
....keep you posted when my new ATMEGA2560 will arrive...

Re: Broken Thermistor killing the GT2560 V3.0 board

Posted: Fri May 17, 2019 12:26 pm
by _kaktus_