Fan PWM output 0V umo+ board - Solved -Not solved :(

[neotko 1,417]

Hi, sorry to post this again but I have zero confidence on this new forum-facebook-scroll-thingy.

I been using x4 new fans on my umo+ connected to the fan pwm output. It was working great but yesterday the fans started to stay on after a print and I had to pwn off/on. They did seem fine. Also noticed that because My mistake the fans where at 40% but without moving for 20minutes so the power must have bounced back and burn something.

Anyway at the end of the day the fans didn't start anymore no matter the pwm setting I choose. I did check the voltage output and now it's a flat 0V no matter the setting. Also tested placing the led strip to that exit and it stays obviously off.

The last time this happened to me was when using a crossflow fan of 340mA and I did burn the bc817 transistor. This time the voltage stays at 0V and I don't know what component could do that. Anyone have any idea? I'll try to change the transistor again in a few days when a friend of mine that has the special solder and tools for this kind of board comes to give me a hand.

Oh also trsted the fans with an external pwm 'thingy' and they work perfect.

Edited September 15, 2015 by Guest

[neotko 1,417]

@amedee I'm rebuilding the marlin firmware from your repository (to change led pin to fan so I could at least recover some functions on this printer) and I was able to set dual extruders and all the basic stuff, but I don't know where should I rewrite to enable to fan info on the ulticontroller. It's not biggie but It would be great to have it if you can just point me to what to search.

I have installed a pwm external controller so I can have a real barrier to avoid killing the led circuit in the mean time.

Also did check again the voltage output and on the fan pwm I get 0.06-0.10 constant, just like on the led pwm when it's off. But the numbers don't change even at 255.

Hopefully it's just the transistor and I can change it in a few weeks when my friend comes with his equipment.

[amedee 349]

@neotko -- You just need to

#define DISPLAY_FAN

either somewhere in the Configuration.h file (does not matter where) or from the make command line in the "DEFINES=" (that's what my builder does)

[neotko 1,417]

Well just to close this. It was the transistor, again... Thank you very much @jonnybischof for answering my pm. I changed also the resistor just to be sure, but the tests outside show that it was working as intended.

Also just for the future I'll work with a 12-24v PWM external box with a big-ass diode to avoid any futher dmg on this board. At least if something blows it just costs 5€ on ebay.

So if anyone else want to test big ass fans on their umo+/um2 and want to avoid killing the transistor bc817...

https://www.youmagine.com/designs/pwm-external-case

[jonnybischof 60]

Very nice print quality on that box!

Just to note: The Ultimainboard does have a flyback diode on the PWM fan output, so there should be no problems. Yeah, the "npn transistor instead of mosfet" solution is kinda crappy, but it's what they chose to do...

The diode you got there could take on 1000 PWM fans

Edited September 4, 2015 by Guest

[neotko 1,417]

Thanks @jonnybischof for all the help.

The print quality now with gt2 and misumi shafts it's quite ok even at 75mm/s.

I have update the pwm box so it fits better and looks better. If anyone want to install more than 250mA fans to the umo+/um2 board and want a cheap solution to avoid killing the transistor this it's a great solution. It also allows me to do some pwm on fans that the board by default can't.

https://www.youmagine.com/designs/pwm-external-case

[neotko 1,417]

I'm starting to hate this board. The fans just died again. Not the output on the pwm fans it's at max. So again I can't control the fans. Again. I assume again third time now the transistor must be dead.

Does anyone knows anyway to make an external pwm that can be controlled by marlin so I can stop getting smashed by just 325mA fans.. This is really depressing.

On the good side I learned solder to fix smd boards...

Also anyone knows if the bc817 exactly the specs of it? On the ultimaker 2.1.1 documentation there no indication of exactly the bc817 that's it's used and I'll like to install one that it's really the exact transistor model.

[jonnybischof 60]

I doubt that the source of the problem is the transistor. It may be dead, ok. But it's pretty much impossible to get multiple faulty parts in succession - there must be another culprit tat lead to this failure.

So, did your external PWM board fail, or was it the Ultimainboard again?

Btw, I'm doing military service atm so I'll be slow to respond...

[neotko 1,417]

Well the pwm board works perfect I can manually control the pwm but the ultiboard it's sending again max power all the time.

My friend that knows about this stuff told me to make an external board connected to the board. Our idea (his) it's to make a board connected to the ultiboard and control it changing marlin to have a good stop. He's theory it's that because the transistor max (high) its 1 amp the x4 fans make a high point of more than 1amp frying the btransistor max. He's going to bring an osciloscope to check the fans highs and if it's that I'll start planning the board connected to ultiboard and changing marlin to control it reassingin the pin table.

It's weird how fast the transistor dies :S I have bough new transistors bc-24 and got some resistors also but last time the resistor was giving exactly 1kohm so on paper it's working.

[gr5 2,224]

Your friend seems smart. I like his theory. Fans are complicated and different manufacturers fans can have very different characteristics. The average flow of 340ma is just average. The peak flow could be much higher.

Also I wonder if the flyback diode is working on your um2 board. Did you blow the diode on the LED circuit also? Or did you never get the alternate circuit working? It seems unlikely that the flyback diode of both circuits would be bad but if you have only ever blown the bc817's in one position then I would definitely suspect the flyback. It may be difficult to test the flyback except when the bc817 is removed so that is a good time to test it.

[neotko 1,417]

Thanks @gr5. We will check the flyback since it's the third time I blow the transistor.

[neotko 1,417]

Well the transistor was toasted. @gr5 We did check the flyback diode and it's working perfectly. Resistor also was just great. Everything was just ok. So this time I changed the transistor (my friend was guiding me a bit so I finally get the hang on this).

We review my notes (I'm crazy like that, I like to note everything about the printer to have a diary when doing any change) and the 3 times the transistor died the fans where at max setting (or close to) and I did shutdown the machine by turning off the power button. It's weird that the energy from the fans can hit the transistor this way. Probably it's that the spike of the fans just sometimes it's bigger than what we measured and it forces the transistor to go beyond his limit.

Anyhow, this means that this x4 414H ebmpapst 66mA each (1.6W) so that's 264mA ain't good for this board. I'll try with my other x4 414 (1W) 144mA. Hopefully this ones won't kill the board. I'm a bit tired of this board fans pwm limitation.

Kapton really makes this easy to remove the transistor with an hotair solder. Peace of cake!

[neotko 1,417]

Btw anyone knows if the BC817 NPN transistor could be just replaced by other transistor that could hold better the spikes? Maybe a BC818? If anyone knows even if it's posible I'm ready to be the test dummy.