Fixing broken power supply?

Have been using my FolgerTech Prusa i3 printer for a few weeks now, and was doing some cable management when, "Pop!" goes the power supply.

I had the mains power unplugged from the power supply, and didn't connect or disconnect any other wires. I was working on hiding some endstop cables (That i will probably just go ahead and shorten later) and when i was satisfied with the job, i went ahead and plugged the printer back in. Pop! Immediately unplugged the printer to prevent further harm. Sounded as if a .22 went off in my room. No burning or acidic smell, just a pop. From the sound of it, i assumed it had to be the power supply. So i examined everything, the ramps boards, the arduino, etc. Nothing. Everything looks fine. I remove the power supply from the printer, and plug it back in. LED light stays off, no more sounds. Using my multimeter, i checked the output voltage, and sure enough, it's dead.

So i go ahead and crack the power supply open, and begin examining the components.
Absolutely nothing.
All the caps look fine, no charred marks, no scorches or burns. No component looks any different than its functional counterpart. Beyond the cheap chinese soldering job, the board looks fine.
So i take the board off of the metal plate to examine the backside. Solder splatter everywhere, but no shorts or anything (It worked for about 3 weeks.). I do, however, notice that there is a nice dry joint on one of the large capacitors. Thinking that might be the problem, i go ahead and fix the joint by reflowing the solder. Put it back in its case, plug it in, nothing.

Anyone have any idea what may have happened?
I am a student who currently doesn't have 30$ to fork out for another power supply, but do have an arsenal of spare electronic components. (Will eventually buy another power supply, but currently don't have money to set aside for it.)

What should i look for? What blew up? Why does it not work anymore?
If any more info is needed, let me know!

sort by: active | newest | oldest
1-10 of 26Next »

I see the capacitor joint you mentioned I also see a bubble on the side of the 39 ohm resistor beside the terminal bar (Pic 2) Nice pics by the way. wherever the falt is it is not obvious so the only thing I can suggest start at AC in checking with a meter and trace until you do not get power. Do you need suggested test points?

So I followed the trace, and it was all good until I got the the Bridge Rectifier. I did a test on the rectifier, and according to my multimeter, it checks out. However, after the AC goes into it, on the output side, I get ~320v DC... And when I try measure it in AC, I get 0v. Is this a problem? There are caps on that side of the circuit, so could that be it? After the Bridge Rectifier, I don't know which traces to follow.. (Begins branching out, going to the IC, a whole bunch of diodes and resistors, one of the small transformers, etc.)

If you have 220 mains 320 should be about right at the rectifier.

For a short cut in the yellow box line voltage AC and DC out the red boxes beside the yellow box.

If you don’t get AC in the yellow box the trouble is between the rectifier and the mains.

If you don’t get DC in the red boxes the trouble is in the rectifier.

Check the voltage switch, make sure it is working. If I am reading your picks right there should be a voltage between the brown arrows and no or vary little voltage between the yellow arrows.

Next check the light blue box at the light blue box, pink wire positive, black wire negative, next post not sure bottom post positive feedback to drive the mosfets, if you don’t get feedback voltages the mosfets won’t work.

Next check the dark blue box if you don’t get voltages there it is the transformer between the light blue box and the dark blue box.

Next check the green box you should get voltages on 5 of the six pins second from the bottom is not important doesn’t connect to anything.

trouble shoot1.jpg

First off, thanks for the in detail reply!

Uh, I don't have 220v mains... 120v Is what I run on o_o

That’s why I found it confusing.

I get 120v AC in the yellow box, so the fuse and the small transformer looking thing are functional.

In the Red Boxes that are on the rectifier, I get 333.3VDC

Between the brown arrows, I get 120v AC. (And 9-10VDC... ?) There is the large brown polyster cap on the other side of the board on one of the brown arrows, the other is the 120v in.

Nothing/ .008v between yellow arrows (This is the switch.)

I don't get anything from Pink and ground/black... So I assume my mosfet(s) are fried?

Went ahead and checked out the lime green area... Some pin combos outputed ~1.3-1.5VDC... Don't think that is anything though.

So I guess I'll look up a method of testing Mosfets... Strange I don't see any visible damage on them (Though this means nothing.) Am still trying to figure out how it made such a loud noise.

The high voltages on the DC side of the rectifier may be your meter misinterpreting current for voltage with digital meters it can give you weird readings. Your meter is under loaded. See my Instructable Circuit Testing for a more thorough explanation.


It could be your mosfets or it could be your feedback to drive your mosfets.

Between the light blue box and the dark blue box is a transformer with a feedback on the bottom pin in the light blue box. That is the feedback for your mosfets and it may not be working.

The only way to know if it is the mosfets or the feedback, take a wire or a set of jumpers and connect the bottom terminal in the blue box and connect it to the terminal just above the light blue box.

If the mosfets are Ok you should get a voltage at the pink and black.

If you do get a voltage at the pink and black the fault is in the feedback and the rest is too hard to do over the net.

I unsoldered the mosfets (Looking at the spreadsheets, they are actually plain old NPN Transistors... Their model numbers are D13009K... Good luck finding any spreadsheets in english.) and did some transistor tests on them. I have been lead to believe one/both of them are dead, as both give different readings, and according to the "tests" I put them through, they seem to be defective.

Tried looking for legit source to order them from (mouser, digikey, etc.) and couldn't come across anything. I did come across this: http://forums.reprap.org/read.php?1,238385,238543

But that's about it. Any recommendations on what alternative I should order? Possibly something more beefed up/overkill? Seeing as they aren't extremely expensive, wouldn't hurt to order a few and try, right?

I got one in both English and Manderan from here:


It was marked 3DD13009K.

This is a good supplier:


Scroll down click on transistors.

Next click on transistor type.

Next in available filters click on the parameters you are looking for.

Beside "Available Filters" you will see "625 Matches" or something like that.

Beside "625 Matches" you will see "625 remaining"

If remaining is 0 change the parameters until you get 1 or more.

The first transformer that gets electricity has 5 inputs, 3 outputs. No matter which combo of output pins i tried getting a voltage off of, i always got 0v. On the input side, i have "~320-340v DC" going in (Still can't figure that out...) and nothing coming out. There is, however, an array of diodes and resistors right before the transformer, so that may also be interfering.

If i am looking at this board correctly, it appears the diodes are also forming some sort of AC to DC rectifier of somesorts. Why is this needed if there is already one on it?

Its actually suppose to be a 390 ohm resistor (Orange White Brown Gold, unless if I did my conversion wrong) But I end up getting 220 ohm with my multimeter....

Not a bad idea. Will do that this weekend. Would leaving one lead on one of the 120v inputs and the other moving down the traces work, then repeat with the other 120v line?

It looked black in the pic so that would be 390 ohm.

Remember to switch to the secondary when you reach the step down transformer.

1-10 of 26Next »