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conny_g

UM Board 2.1.5 transistors burnt for fan / LED

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Hi,

 

recently I plugged the power adapter into the board with the on/off switch at „on“.

Heard some sizzling noise, then got some burnt smell, afterwards the printer was dead aside of some glowingof the LEDs.

 

The step down converter on the board was burnt (had a hole in its case), part „U6“ not far from the Atmega16u2 that does the USB communication.

It‘s a Allegro A4403 step-down converter, creates the 5V for the board from 24V.

 

After replacing it the board generally works, but two issues are left:

the LEDs are dim, only one segment is bright with one dead led.

the model fan does not work.

 

Both are PWM controlled outputs with a transistor, see linked thread where a similar thing happened.

 

Not entirely sure if the LED output is damaged or if that dead LED causes the problem.

 

Now my question:

 

these outputs burning out, is this a common thing to happen? Anyone experienced this, too?

I am looking for the reason why this happened.

 

cheers,

Conny

 

 

A4403-Datasheet.ashx

 

 

 

 

Edited by conny_g

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Researching about it I find that @neotko killed these transistors a few times, so it seems to me they are in fact a weak point of the board.

 

Thinking about what might have happened.

The power adapter - the chinese one with 360W, not the original - might have significant output capacitance, maybe it even causes a voltage surge when plugging it in.

So possibly it sent that surge across the board on the 24V „rail“, that would hit all components exposed and surely these BC817 and the step down.

Then there is this damaged LED on the stripe, it could be dead due to that as well. 

Or the LED dying actually killed the transistor? But that would not explain why the step-down died.

 

Wondering if that chinese power converter will kill my board more often. But on the other hand I am using the same model on my other printer for 1 year without issues...

Anyway, some more fun to be had with dissassembling the printer and repairing the board another time the next days. Would just ignore the light for a while, but the model fan missing is fatal. Had a really bad print due to that today. That triggers the repair.

Edited by conny_g

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If the LED would be short-circuited, I could imagine that it would destroy its driver transistor. With the power off, you could try to measure with an ohm-meter on the LED, while in-circuit. This method is of course unreliable, but if you would get 0 ohm, then it is at least an indication, and then you might consider removing it. But it seems unlikely to me that the LED would be the cause? It rather seems like an overvoltage spike, causing all the damage, including destroying the LED?

 

I read that a lot of switched mode power supplies cannot generate a stable output voltage if there is no load. Thus this applies to almost all modern supplies with tiny transformers running at high frequencies, instead of the old huge and heavy transformers running at 50Hz. These modern switched mode supplies need a minimum load to work well. So I could imagine that the output voltage would have been way too high, due to no load, and that your board got an overvoltage spike when you inserted the plug, and the overloaded capacitors discharged into your board? This is just guessing, since I don't know the circuits of the UM-board nor the supply, but it might be an explanation.

 

Some of the better switched mode power supplies have provisions to switch off the output if there is no load. Or they have an internal resistor over the output, to always give it enough load to be stable (the old Delta Electronics supplies had this, around 1990). But maybe yours doesn't?

 

But normally both the power supply and the printer board should have overvoltage protection diodes (transzorbs or zener diodes?), to absorb such spikes. I don't know if the UM board has these? Or maybe they weren't up to the charge?

 

It is best to only connect such power supplies with the main power off, and the supply discharged before connecting. To discharge it, place a suitable lamp over the output, for example you could use a suitable car or truck lamp, and solder wires on it. (Not a LED, unless you put a suitable resistor and protection diode in series with it, or unless you put two LEDs in anti-parallel, and that in series with a suitable resistor.)

 

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10 minutes ago, tinkergnome said:

The nozzle looks interesting - is it something special?

 

Good point, need to check that when back at the printer. Just had a quick look & photo in the morning.

It’s a 3D Solex Matchless block and nozzle. Looks like the nozzle is unscrewed and flooded with filament....

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1 hour ago, neotko said:

Check the small fan. It also has a transistor. Just in case...

 

The hotend fan works. Also checked the transistor via diode test and it was ok.

 

I have only two things open from this Mark 2 build and board repair: 

- the E2 feeder (Bondtech) seems to have issues. E2 tends to underextrude and it makes decent strange clicking/crackling noises while extruding. But it does not grind. Interestingly I have swapped extruders for the dual mod (former E1 became E2) and that printer already had issues with the feeder before. So I should disassemble the feeder and see if there is something broken.

- E2 model fan not working. Next steps: factory reset to make sure it’s not software. Double check firmware. Unplug and power the fan directly. Check expansion board connections. Check output signal of expansion board.

Edited by conny_g

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Finally a first "two-color cat" with the freshly built Mark 2. The back is not very clean, forgot to switch on the "Mark 2 Tweaks".

Disassembled the feeder, did not find anything unusual. 

Found that I used an old version of the firmware, whyever I did that late in the night :-) Hope that's the reason for the E2 model fan not working.
So I updated, reset the firmware, configured the parameters. Now calibrating and then another cat.

 

fullsizeoutput_1cb1.jpeg

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I have 2 UM2+ and three original boards, fried one two years ago. Unfortunately the repair of that failed. Changed the Atmega16u2 on that which works again now, but now the board has other issues (m2560 can be flashed directly, but not through USB and the board won’t start, display stays dark). Currently no time / enthusiasm to look further what the problem is.

 

So I am actually considering of buying a chinese one as spare. It seems the frying of boards happens every 1-2 years :-)

Which board or seller could you recommend?

Any issues with the chinese I should be aware of or is it plug & play?

Edited by conny_g

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I had two china clone boards, one was running for year and a half without issues. The only issue I had with them is that the fan/led molex plug was inverted (the plastic) other than that no issues. Can’t recommend a seller since the ones I bought from have removed the product 

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38 minutes ago, neotko said:

I had two china clone boards, one was running for year and a half without issues. The only issue I had with them is that the fan/led molex plug was inverted (the plastic) other than that no issues. Can’t recommend a seller since the ones I bought from have removed the product 

 

And how did the china board "end", by being replaced with Duet3D or did it fail? And the other one? :-)

 

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2 hours ago, conny_g said:

 

And how did the china board "end", by being replaced with Duet3D or did it fail? And the other one? :-)

 

 

I have 2 original um2 and 2 china on a bag, for a rainy day. But probably if I build a fourth one would also be with duet3d 

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