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I have 12 V/30 A PSU. I have also installed the firmware onto the Arduino Mega2560. But the problem is that the display on the LCD keeps turning on and off automatically (it's stuck on the Marlin logo because it keeps restarting).

When I hear the PSU fan, it also turns on and off automatically. I suspect that there is something wrong with my PSU because when I supply power directly using the Arduino Mega's port, the display didn't repeatedly restart automatically.

When I connect an LED to the PSU, it blinks. It blinks and continue goes normal. It keeps repeating like that.

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    $\begingroup$ Connect a voltmeter, scope, or an led+resistor to the PSU output and see if it blinks or stays on continuously. $\endgroup$
    – Navin
    Mar 8, 2022 at 2:30
  • $\begingroup$ It could be broken, buying a spare doesn't cost much and you'll be able to troubleshoot. But, since you have supplied another power source which doesn't show the intermittent on/off behavior, it is most likely the PSU is faulty. $\endgroup$
    – 0scar
    Mar 8, 2022 at 10:04
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    $\begingroup$ Does the PSU behave in the same manner when not under load (without the printer or anything at all, connected)? Without photos of the inside of the PSU, or any results of testing various components within the PSU, it's going to be rather difficult to provide a definitive answer. $\endgroup$
    – Greenonline
    Mar 8, 2022 at 12:42
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    $\begingroup$ Previously you had said that when an LED was connected to the PSU, then the LED blinked - giving the impression that only the LED was connected to the PSU. Now you are saying that with only an LED connected, the LED does not blink..! If previously you had connected the LED to the PSU, whilst the PSU was still connected to the RAMPS and exhibiting the stop/start behaviour, then obviously the LED would blink as well. So, to clarify: When not under load, the PSU is fine (both the old and the new PSU), but when under load the PSU stops and starts... is that correct? $\endgroup$
    – Greenonline
    Mar 9, 2022 at 6:01
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    $\begingroup$ To me, if seems like you are attempting to draw too much current from the PSU, and it shuts down momentarily, as part of its self-protection. That seems to be the most logical, and obvious, reason. Try disconnecting one of the high current draw devices, i.e. the headbed, and then see if the PSU works OK. If so, then the heatbed needs a separate supply as per my previous answer. $\endgroup$
    – Greenonline
    Mar 9, 2022 at 6:05

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Simple answer

If the PSU continuously restarts, even when not under load, i.e. nothing is connected to it, then it is clearly faulty.

If you then connect this faulty PSU to a 3D printer then the printer will not work either.

The long and short of it is: The PSU is faulty; buy a replacement.

Given your previous questions, and apparent high current requirement (heatbed, etc), you may have damaged the PSU by attempting to draw too much current. If so, then any similar spec'd replacement PSU will probably suffer a similar fate as this one.


Guesswork answer

As to why it is restarting could be down to a number of factors. The most common failings of LED PSUs (assuming that is indeed what it is) is one (or both) are the power FETs (usually there are two of them), which are bolted to the side/rear of the case. This fix is to simply replace them, like for like.

The FETs are by no means the only possible issue - there could be a faulty/blown capacitor, or any other of the components. The only way to tell for sure would be to open the case of the PSU and visually inspect the PCB for burn marks, and maybe thereafter probing it with a DMM.

However, if you don't know what you are doing, then don't attempt this as as mistakes could well be dangerous and/or fatal.

IMHO, cheap unbranded LED PSUs have a notoriously bad reliability. You will probably find that you have better luck using a branded ATX PSU for a PC instead.

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