faulty gt2560?

[ash2k14]

Hi, I ran into 2 problems on my gt2560;

1. I tried to use the drv8825 that were correctly installed and everything was wired correctly, however, when the motor was plugged in, the stepstick became hot all of a sudden approx. 90'c++, and I didn't try to move the motor. Also, disconnecting the motor would seem to calm down the stepstick, but this doesn't make any sense why the stepstick would go rogue in having the temp being so high when the power was poured in. I also turned the potentiometer to counterclockwise direction and it is still the same. This however doesn't affect my A4988, the temperature were okay which lead to the next problem

2. In this problem, I got mintemp error, where the error suggests that I don't have thermistor or the thermistor legs were shorted. I tried swapping the plugs out but the results were the same. As far as I know, the thermistor input pin are right next to the reset button. I also tried the plug on my old sangui 1.3a, my sanguino board shows the thermistor is present. However, on the gt2560, it gave me error, I tried everything, none seems to work

[Mark]

1) what is the voltage of the 8825? measure the voltage of the potentiometer when powered with USB. you can compare it to 4988 to see the different .
2) Mintemp must be a open circuit of the thermistor. How about the readings at room temperature when not heated up? the one that show 0℃ at room temperature is bad contact with the outlet , you can plug and unplug it for several times to check it .

[ash2k14]

I tried measuring the voltage reference, from the +5v point to the left of the atmega chip and the pot screw, it shows me a constant 5.0xxV even I tried to turn it on the drv8825, on my spare a4988, it shows roughly about 3.7xxV, I moved the probe to the main power input and the volt on drv8825 shows about 0v, while the a4988 shows around mv or 1.3v max. When turning it in clockwise, it somewhat resets itself again to mv values

About the thermistor. I don't understand why it won't work on this gt2560 even though it really works on my sanguino 1.3a now. My room temp here is 28-32, this board however throws me max temp error if I remember correctly. I did try measuring some resistance on the thermistor input pairs, the meter returned about 8.7k value. All the pairs are the same values

[Mark]

"MAXTEMP ERROR:
1. If it shows "358/0, room temp/0; Err: MAXTEMP". The extruder thermistor is short.
2. If it shows "358/0, 358/0; Err: MAXTEMP". Both extruder thermistor and hot bed thermistor are short.
3. If it shows "room temp/0, 358/0; Err:MAXTEMP BED". The hot bed thermistor is short.
Please check if somewhere of the wire are connected. If so, the current will not go through thermistor, and LCD will diaplay TEMP ERROR ."
And the voltage should be measured like this:

[ash2k14]

Both reported max temp error, however, both physical thermistor legs are not shorted and I tried it in my sanguino 1.3a board and it reported okay at room temp of 28-32'c

I will try again on measuring the voltage value

[Mark]

So if the thermistor works fine then must be something wrong with the board or heating parts.
You can check the resistance of the hotbed and heating cartridge, when not plugged into the board, it should be 1.5ohms for hotbed and 3.6ohms for the cartridge.
And to check the board, unplug the thermistor or short the thermistor out, if it reads 0 or 385 at room temperature then the board is OK.

[ash2k14]

I tried connecting the board (only with my drv8825 plugged) using pronterface, the board returned maxtemp error (no thermistor connected).

Also in accordance to voltage measurement from pot and gnd pin for stepstick, I get 0v on my drv8825, not tested on a4988 yet

[Mark]

Which firmware are you using? Have you reinstalled it?

[ash2k14]

Yes, in fact, I used the same firmware that i'm using for my sanguino. But even reflashing the firmware wouldn't solve anything because it is the physical pins that were shorted within the board, the firmware is just to drive the electricity

[Mark]

Then you'll need a new board.