Printer heating bed switches off

[Hajo]

Recently the printer heating bed switches off after 1-2 hours of printing time and the printer part comes off the printing plate (all other functions are ok). After cooling all printer parts to room temperature, I can start the printer again with full function. After some time the heating will turn off again.
Is the power supply overloaded and turns off or is this a motherboard error?
Note: The printer has worked flawlessly for many hundreds of hours and this error occurred for the first time after a 20-hr. print.

[_kaktus_]

Hello.


In my opinion, your reasoning is good.

If an important electronic component starts to overheat, the symptoms you describe may occur.
Now you have to find out which element contributes to this.

As you suggest in the first step I would check the power supply.
You can connect a voltmeter to it and monitor the readings during operation of the printer.
You can also use another PSU.

[Hajo]

Thank you for your prompt reply.
Here's an update: In between, the heating did not work anymore. A check of all voltages directly at the PSU resulted in 12.35 V at all outputs and no voltage at the print bed connection. After a reset on the mainboard, the function was back.
The printer works for about half an hour and then I could see that the heater failed several times briefly and then worked again until the final failure.
Standby mode: all PSU outputs 12.5 V.
during printing: all PSU outputs 12.31 V, print bed 11.4 V.
The print bed has a resistance of 0.7 ohms at room temperature.
Is it a motherboard error after all?

Hajo

[_kaktus_]

Hi.


In order to make a good diagnosis it is necessary to measure the voltage of the power supply during a preheating failure.

[Hajo]

...Sorry, I forgot to write:
When the error occurs all voltages at the PSU are normal (12.5V) and at the heating bed 0.0V.
Is the heating bed resistance normal with 0.7 ohms? In some posts I read 3.5 ohms. (12.5V / 0.7ohm = 17.8 A !!!).
thank you for your help
Hajo

[_kaktus_]

Hi.


You have now given very important facts.

As you noticed yourself, this is not normal.
Probably somewhere is a short circuit. Do you use metal clips

[Hajo]

No, I do not need metal clips, heating bed and Superplate are firmly connected.
A test with a replacement PSU gave no other results and I can find no damage to the heating bed. As a precaution, I have desoldered the power indicator - LED + resistor to exclude a short circuit.
Conclusion: I will order a new heating bed!
Thanks for the help

[_kaktus_]

Hi.


You know what ...
Take a very careful look at the connectors to which the cables are soldered. Maybe there is short circuit there.
You can also try to change the configuration to a typical 24V configuration and perform a test.
Then the resistance of the circuit is higher.

[Hajo]

New development :
Now I have done a printer test without bed heating, the printer has worked perfectly for 8 hours, then there was a loud bang and all fuses turned off. The control on the PSU returned 0V at all outputs. I have seen that the PSU is actually designed for 41 A, a heating current of 17-20 A on the heating bed should not be a problem. Has there been a mistake in the PSU in advance?

[_kaktus_]

Hi.


In my opinion, the power supply could have been overloaded earlier.
And now the inevitable has arisen.

Not so often, but I regularly observe problems with these power supplies.
Will you show his photographs