Fried component (transistor?)

Hi there

I am in the late stages of my build and have been testing moving of axis’ and sorting out limit switches/homing etc.
I was having issues with the USB connection to the PC dropping out after a handful of moves so i installed a 5v 1a voltage regulator (7905CT) and attempted to connect via ethernet to fix the dropout issue.
At the same time i added a proper 24v PSU (had previously been running off a spare 12v unit for motor power) and 2x drv8825 drivers wired to spare GPIO pins (7 axis/4 head build)

When i first fired up the board with the new setup i had stable LEDs for VBB and 3.3v, no connection LEDs lit and seemingly no issues.

I plugged the ethernet cable into the PC and immediately all the magic smoke escaped from the component circled in red:
edit -cant post an image/link as a new user?
Fried part is the transistor looking thing immediately to the right of the voltage regulator connection, slightly up and left from the 1,2,3,4,3.3v,vbb LEDs when viewing the board with the mosfets to the top and USB to the right. Hope this is clear enough!

I immediately removed the ethernet cable and cut mains power to the PSU however the component circled is fubar,

Can somebody please provide me the part number (and maybe some alternatives, many overseas part numbers dont seem to work here in Australia, which is why i used a 7905 regulator)

If anybody has any theories as to why it fried itself and or possibly even my USB connection issues i’d be very appreciative. I really need to get this sorted asap.

Thanks in advance

Imported from wikidot

Le 7905 est un régulateur de 5v négatif (-5v) le brochage est différent du 7805 de plus le 7805 a une tension d’entrée plus faible que 24v il faut employer de préference le régulateur préconisé ou des régulateurs ayant une tension d’entrée supérieure à 30v

Merci pour votre aide Patrick .
Je ne suis pas bon avec l’électronique et ne suis pas sûr si le 5v négative fait une différence à part les affectations des broches ? Je l’ai remarqué et Bent broches de sorte qu’il est câblé au smoothieboard correctement.
Les broches i utilisés sur le régulateur sont : (de gauche à droite)

Si le régulateur de 5v négative est correctement câblé , ce sera toujours la cause de mon problème ?

Toutes les suggestions pour une partie # pour remplacer le transistor frit ?

Merci pour votre aide!

Thanks for your help Patrick.
I am not good with electronics and am not sure if the negative 5v makes a difference apart from the pin assignments? i noticed this and bent the pins so it is wired to the smoothieboard correctly.
The pinouts i used on the regulator are: (left to right)

If the negative 5v regulator is wired correctly, will this still cause my problem?

Any suggestions for a part # to replace the fried transistor?

Thanks for your help!

Ok ive had a look at some pictures on the google and it looks like the component ive fried is IC10 (LM1117-3.3v)
I cant find these at my local electronics store (Jaycar Electronics), can anybody suggest an alternative part number or what specs i have to look for in a similar voltage regulator?

Sorry but I do not speak English, but the 7905 is a negative regulator 5v ie it receives a negative voltage (9à20v) and when it delivers the output -5v pinout is different from 7805 and is not going to the application on the smoothieboard, that the regulator is 3.3V hs is explained by the different pinout therefore the output of 7905 is not the same place as the regulator for + 5v

Hi Andrew,

not sure if you already fixed your mistake, but you definitely need a positive voltage regulator like a LM7805 and NOT a negative one like the 7905 you’ve used. I think there are a lot of other types that should work, important is that you choose a fixed voltage type (not an adjustable one) and make sure it can handle your input voltage (24VDC i assume).

Next you need to replace the LM1117 3.3V if you fried that one.

Check out RS components Australia:

LM1117 3.3V

Hope that helps!

Thanks bouni

Ive already obtained a LM7805 to replace the negative regulator, but havent got a LM1117 yet. RS Components are around 1.5hrs drive each way from me, the closest 3.3v regulator i can find at my local electronics store is a LM3940 (3.3v out, 5v in, 1a). Will this be a suitable replacement or am i going for a long drive to get the LM1117? Postage from RS takes 2-6 weeks in my experience :frowning:
The LM1117 seems to be fed from the LM7805 5v regulator, so can i assume that it is only getting 5v?


unfortunately the LM3940 has another pin out than the LM1117! You could use it as a quick hack to make it work again and order an LM1117 to replace it later on.

You could use wires to connect the right pin tho the corresponding pad.

Thanks mate, I’m aware of the different pinout, but if the other specs are within range I will give it a try temporarily to check if the rest of the board is still OK then swap it out for a proper lm1117 from RS as you suggested.
Thanks for your help!

le lm1117 est un régulateur ajustable! brochage et utilisation différente, quan au lm7805 il peut aller pour une alimentation en 12v mais pas pour du 24v la tension d’entrée 24v est trop élevée pour lui, il vaut mieux utiliser le régulateur préconisé

Hi Andrew,

The LM1117 3.3V i linked above is a fixed 3.3V type like the originally used one is.
It is supplied by the 5VDC coming from the USB or the R-78E5.0-0.5.

For details check the schematics, 3rd page lower left corner.