GT2560 heated bed failure, MOSFET LED blinking

[tml]

Hi,

I recently installed a GT2560 in my Prusa printer. I am having some trouble getting the heated bed to work and I suspect that it's a control board problem, I need someone to confirm that what I am observing is not normal.

The control board is getting 12V from a 15Amp power supply.
When I turn on power, the 2 control lights next to the power input are lighting up and 2 fans start spinning.
When I try to turn on the hot end, the LED next to the hotend MOSFET lights up and the hot end starts heating up. This is normal behavior.
However when I try to turn on the heated bed, the following happens:

• fans turn off
• LED next to the heated bed MOSFET starts blinking (about 3 times a second)
• both control LEDS next to the power input start blinking (same frequency as the MOSFET LED)
• if the hotend heating was on, it stops and the hotend starts cooling back

I checked the SMD fuses and they seem to be okay. If I swap them, same result.
I also tried connecting the heated bed to the hotend's MOSFET, it couldn't heat it up either (its LED was blinking, not constant lighting).
I measured the resistance of the heated bed, it seemed to be normal, around 1.5 Ohm.

Is this a GT2560 problem?

[William]

Hi,

I recently installed a GT2560 in my Prusa printer. I am having some trouble getting the heated bed to work and I suspect that it's a control board problem, I need someone to confirm that what I am observing is not normal.

The control board is getting 12V from a 15Amp power supply.
When I turn on power, the 2 control lights next to the power input are lighting up and 2 fans start spinning.
When I try to turn on the hot end, the LED next to the hotend MOSFET lights up and the hot end starts heating up. This is normal behavior.
However when I try to turn on the heated bed, the following happens:

• fans turn off
• LED next to the heated bed MOSFET starts blinking (about 3 times a second)
• both control LEDS next to the power input start blinking (same frequency as the MOSFET LED)
• if the hotend heating was on, it stops and the hotend starts cooling back

I checked the SMD fuses and they seem to be okay. If I swap them, same result.
I also tried connecting the heated bed to the hotend's MOSFET, it couldn't heat it up either (its LED was blinking, not constant lighting).
I measured the resistance of the heated bed, it seemed to be normal, around 1.5 Ohm.

Is this a GT2560 problem?

Hi,
You can have a try to the followings:
1.Check if the heatbed fuse was broken.
2.Check if the heatbed mosfet is normal.
3.Can you attach a LCD pic after you connect the heated bed cable to the hotend port.
You can find more details in this link:http://www.geeetech.com/forum/viewtopic ... 19&t=17039

[tml]

Hi,
Thanks for the link to the guide, I was already following that one when debugging the problem.

Fuses:
The fuses look completely intact. I cannot measure any voltage drop on them, I also tried swapping them and it's not making a difference.

MOSFET:
The MOSFET looks visualy okay. I tried measuring the voltages between the heated bed MOSFET's GND and the fuse (as described on http://www.geeetech.com/forum/download/file.php?id=1578) but I could not measure a voltage difference there when the lights were blinking. It was definitely not 12V as it was supposed to be. But I still do not think that this was a fuse problem as swapping the fuses do not help and I also tried connecting the heated bed to the hotend's MOSFET and I got the same blinking result, even tho when I have the hotend connected there it heats up nicely.

LCD:
I attached a screenshot of the LCD

I also did some more debugging. If I do not connect my computer with USB and use the LCD controls to heat up the bed, the firmware resets. You can see it here:
https://www.youtube.com/watch?v=dnwPgx6NZ2w

If I have the computer connected over USB and use Printrun to heat up the bed, the firmware does not reset but I get this strange blinking on the board:
https://www.youtube.com/watch?v=Oloh4mXtfew

Is it possible that with the heated bed on the whole electronics reboots and reboots and reboots and that's why it seems to be blinking? What do you think this is, control circuit problem or maybe a power problem? I know that a 15A power supply is not very powerful, can that be causing a behaviour like this?

[William]

Hi,
Thanks for the link to the guide, I was already following that one when debugging the problem.

Fuses:
The fuses look completely intact. I cannot measure any voltage drop on them, I also tried swapping them and it's not making a difference.

MOSFET:
The MOSFET looks visualy okay. I tried measuring the voltages between the heated bed MOSFET's GND and the fuse (as described on http://www.geeetech.com/forum/download/file.php?id=1578) but I could not measure a voltage difference there when the lights were blinking. It was definitely not 12V as it was supposed to be. But I still do not think that this was a fuse problem as swapping the fuses do not help and I also tried connecting the heated bed to the hotend's MOSFET and I got the same blinking result, even tho when I have the hotend connected there it heats up nicely.

LCD:
I attached a screenshot of the LCD

I also did some more debugging. If I do not connect my computer with USB and use the LCD controls to heat up the bed, the firmware resets. You can see it here:
https://www.youtube.com/watch?v=dnwPgx6NZ2w

If I have the computer connected over USB and use Printrun to heat up the bed, the firmware does not reset but I get this strange blinking on the board:
https://www.youtube.com/watch?v=Oloh4mXtfew

Is it possible that with the heated bed on the whole electronics reboots and reboots and reboots and that's why it seems to be blinking? What do you think this is, control circuit problem or maybe a power problem? I know that a 15A power supply is not very powerful, can that be causing a behaviour like this?

OK,looks like everything is ok.I guess it is caused by the unstable DC output.Some questions and tips:
1.Was your heatbed rated voltage is 12V？
2.Did your fans voltage reach 12 V when you're heating up the hotend?
3.What happens when you exchange the hotend cable and the heatbed cable on the motherboard?
4.Try another PSU if you have one in your hand.

[tml]

Hi,
I checked the setup again and found that the power supply was making a clicking noise, so your suspicions about it having an unstable DC output seems to be holding. I also did a more precise measurement on the heated bed and it only seems to have 0.4A resistance which is way too low for a 15A power supply, so as of this moment I am ruling out a control board problem. I'll try getting hold of another HB or a power supply. Thanks for your advices!

[William]

Hi,
I checked the setup again and found that the power supply was making a clicking noise, so your suspicions about it having an unstable DC output seems to be holding. I also did a more precise measurement on the heated bed and it only seems to have 0.4A resistance which is way too low for a 15A power supply, so as of this moment I am ruling out a control board problem. I'll try getting hold of another HB or a power supply. Thanks for your advices!

Hi,
Looking forward to your good news!