So yesterday I got my power supply in the mail and I thought, let's check it out!

I put all the wires in correctly (as shown in this YouTube video, Anet A8 power supply unit fuse blown, I just searched really quickly, this person has the same problem as me) and "BANG", it blew.

Image from YouTube video

Luckily the only thing broken on it is the fuse, for which I can get a new one, but my main question is .. why? why did it blow out? Did I wire it up wrong? The 12 V output goes to a RAMPS 1.4 board which is working correctly.

It worked the first time I plugged it in; the little green light went on. The second time a nice "big bang". When I tested it the first time, I didn't add the 12 V wires to the RAMPS board yet. When I did, the fuse of the PSU blew out.

The board is a RepRap RAMPS 1.4, which works fine when connected via USB to laptop.

Upon closer inspection I found a burned out resistor in the circuit of the power supply, maybe this caused the bang?

BIG update!

I opened it up and flipped the board, and noticed that there was a big ol' blob of tin connected to one of the pins I connected my wires to. I am very sure that this blob shouldn't connect to that pin at all, hence shorting my board.

Is this the cause?

Close up of PCB

Close up of PCB - Highlighted potential short circuit

Here is a link to the webpage I bought it from: Anet® 12 V 20 A 240 W Power Supply Dual-input Centralized Power Monitoring For 3D Printer

Here is how I wired it up at the PSU side:

Power supply connections

At the RAMPS side:

RAMPS board connections

This shows the internals of the PSU, it clearly shows burn marks:

Overview of the failed electronic component in the PSU

  • $\begingroup$ I think we also need to see how things are connected on the other end before we can help you see where you went astray or if there indeed is something wrong with the power supply. It appears from the picture you have up you installed the wiring correctly (except for the missing ground as 0scar pointed out in his answer). The controller end of the equation is important, because if you've crossed something up on that end, you're most likely in for an issue as well. $\endgroup$ Commented Feb 10, 2019 at 18:47
  • $\begingroup$ Added images from your imgur link ... it looks like your board is fried to me, but I'm not an electrician. Disconnect the power from the supply to the board, replace the fuse, then plug it in and check the voltages coming from the power supply to verify it's still good. If it is, the main board is going to need replacement is my bet. $\endgroup$ Commented Feb 10, 2019 at 19:26
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    $\begingroup$ The "burned" image is from the power supply? Sorry, that wasn't made clear, but if so, yah, power supply no good! ;-) $\endgroup$ Commented Feb 10, 2019 at 19:32
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    $\begingroup$ @Pᴀᴜʟsᴛᴇʀ2 Always nice to see people have the hammer close by in case of emergency! ;) Please try to keep the workspace clear when using electronics, metal screwdrivers laying around is not optimal. $\endgroup$
    – 0scar
    Commented Feb 11, 2019 at 8:30
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    $\begingroup$ The resistor shows burn marks, but these are residues from the other component next to it (4-way diode?). I think this question is best asked in the Electrical Engineering Stack. In reaction to ` Thank god my ramps board is still okay!`; what makes you say that? You have no reason to assume that from this experiment. Is this your second PSU, as the Anet A8 comes with a board and PSU as it is a complete kit, you need to add more information. What kind of PSU did you buy? (make and model or link/image of info plate) $\endgroup$
    – 0scar
    Commented Feb 11, 2019 at 8:49

2 Answers 2


You need to closely look at how to connect to the output connectors. In this case it appears that you have wired it correctly according to the stamped in markings above the connectors. You have chosen not to connect the earth, this is strongly advised.

Did you check if the power switch matches the voltage of your country? If you are in Europe the switch should be set to 230 V, not 115 V (which is used in America).

E.g. for the following power supply you see such a switch on the side: PSU voltage setting

If a PSU is connected without load and works, and short circuits when externals are connected there are a few options:

  • there is a short in the connected printer board,
  • the load that the board takes is too large for the PSU,
  • the PSU cannot deliver the load,
  • the PSU was faulty to begin with.
  • $\begingroup$ Hello! I just found this youtube video after i blew it, finding out he used the same method of connecting it as me. The voltage switch is on 230V, which is correct. I looked at charts which told me to connect it this way. $\endgroup$ Commented Feb 10, 2019 at 15:48
  • $\begingroup$ Dear oscar, the board is a ramps 1.4 board that doesn't short when i connect it to my laptop via a usb cable. the lights all flash nominal. I don't think it really takes such a big load, since most 3d printers use it, and i didn't connect any motors to it yet. If it's broken, then how do i prove to Banggood (ironic name) that it wasn't my fault? $\endgroup$ Commented Feb 10, 2019 at 16:30
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    $\begingroup$ @wesseldijkstra "If it works over USB" has no relation to powering it with 12 V. $\endgroup$
    – 0scar
    Commented Feb 11, 2019 at 8:35

Unless you know what you're doing, do not remove the covers from a PSU. The components can store a lethal charge long after power is removed, even if the fuse is blown.

My guess is something loose (now vapourised) in the PSU. Electronics have a tendancy of failing either quite soon after manufacture, or lasting reasonably well. This is described with the Bathtub Curve.

Looking at the failure, there was a significant short circuit somewhere - quite likely within the PSU itself. This doesn't mean you can be sure that the RAMPS board survived, but it has a reasonable chance of not being harmed.

There is no significant chance of the PSU failing like that simply due to an excessive load in its output - unless it was overloaded for a significant period of time. Generally these PSUs will have some degree of overload protection even if they are not explicitly designed to survive an overload.

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    $\begingroup$ No, completely wrong (unless your image is misleading, but I doubt it). This is common technique to increase the current carrying capability of the copper track. It goes without saying that you are not experienced enough to safely work on this with the covers removed. $\endgroup$ Commented Feb 12, 2019 at 9:32

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