Omnibus F4 Flight Controller won't power up when lipo battery is connected but it does power up when USB cable is connected looking for some help to get this FC working again if possible, some help would be appreciated.

The most likely cause is that the 5v regulator which steps the LiPo voltage down to 5v in order to provides the 5v rail with voltage has fried itself. Either that or the diode after the 5v regulator that provides the 5v rail with voltage has gone open circuit.

Do you have a multimeter? If so, test the voltage on one of the 5v pads when you plug in the LiPo.

Which Omnibus F4 Flight Controller actually is it? There are a ton of different versions (and also clones). If you can put a link to where you bought it from that will make it clear.

Watch this. It is likely your problem. BTW, the photos have very low resolution. I can't make out anything.

(02-Jan-2019, 01:12 AM)SnowLeopardFPV Wrote: The most likely cause is that the 5v regulator which steps the LiPo voltage down to 5v in order to provides the 5v rail with voltage has fried itself. Either that or the diode after the 5v regulator that provides the 5v rail with voltage has gone open circuit.

Do you have a multimeter? If so, test the voltage on one of the 5v pads when you plug in the LiPo.

Which Omnibus F4 Flight Controller actually is it? There are a ton of different versions (and also clones). If you can put a link to where you bought it from that will make it clear.

It's Omnibus STM32F4 Brushless i bought it from Banggood power supply is 2-4S i connected 2S to it  i tested the voltage on one of the 5v pads with my multimeter, multimeter show only 1.72v.

(02-Jan-2019, 02:34 AM)voodoo614 Wrote: Watch this. It is likely your problem. BTW, the photos have very low resolution. I can't make out anything.

Thanks for your help i'll watch it.

It is a bummer that it doesn't work. If it is within 30 days, Banggood is pretty good with getting you a replacement.

Where is the voltage regulator on the board does it has two or three pins where is it located on the board?

I guess your board is the following one...

https://www.banggood.com/Micro-20x20mm-B...32495.html

That board is using an MP2359 DC-DC Step-Down Converter (BEC) rather than a standard voltage regulator. Internally a BEC contains some standard voltage regulators along with a load of other components. I've indicated the location of the BEC on the board in the edited image below...




There's a whole load of circuitry around it as shown below that controls what voltage the BEC actually outputs. Input voltage (VBUS) is supplied on pin 5 (IN), and the stepped down regulated voltage (VDD) comes out on pin 6 (SW). If you look at my image above, pin 6 is the one on the top left of the chip, nearest to the 10uH inductor (the square component that has the number "100" stamped on it). Plug a LiPo into the board and measure the voltage going into pin 5 which is the top middle pin (it should be the same voltage as the LiPo), and then measure the voltage being output on pin 6 (it should be ~5v).

Given your issue, it is probably your diode that is bad.

Thank you very much this Forum rocks this forum is awesome other forum leave you stranded scratching your head wondering WTF could be wrong i have two of these boards one comes one when the lipo is connected it and the other comes on when USB is connected to it so i decided i wasn't going to order any more of these boards, instead of just throwing them away why not just try to fix them because that's like throwing my money away i have alot of brush drones but not brushless so since i'm kind of new to brusless i messed them up by mistake.

6 pin shows a reading of 1.71 and the 5 pin shows a reading of 7.41 it's the same as my 2S lipo.

(03-Jan-2019, 02:24 AM)MicroFn Wrote: 6 pin shows a reading of 1.71 and the 5 pin shows a reading of 7.41 it's the same as my 2S lipo.

That does sound to me like it's the BEC to blame then in this particular instance. I suggest you do the same test on the other board you have which powers up fine from the LiPo to see if you get 7.41V on pin 5 and the expected 5V on pin 6.

Flight Controller circuit design seems to follow a general pattern in that the 5V from the USB Port (which has already been regulated so it generally doesn't need to go through the on-board BEC) goes directly to one side of a Schottky diode and then on to power the rest of the Flight Controller.

The LiPo voltage on the other hand needs to be stepped down to 5V, so the VBAT input voltage first goes through the on-board BEC and the 5V that comes out of that then goes into the other side of the Schottky diode that the 5V line from the USB Port also goes into, and then on to power the rest of the Flight Controller.

The Schottky diode effectively acts as a one-way gate only allowing 5V from VBAT-->BEC-->5V-->Schottky-->FC-Power  OR  USB-Port(5V)-->Schottky-->FC-Power . The Schottky will prevent 5V from the USB port going back down the wire to the  BEC / VBAT, and visa versa the Schottky will prevent 5V from the BEC going back down the wire to the USB port.

It isn't a requirement to use a Schottky diode. Two separate standard silicon diodes could be used instead, however the advantage of Schottky diodes is that they have very little forward voltage drop compared to standard silicon diodes so you lose less voltage when going through them which is one reason they're generally used for this type of application.

The text diagram below is my crude attempt to try and illustrate the above description.

EDIT: Replaced plain text diagram with image of the same below to eliminate formatting issues with text wrapping.

(03-Jan-2019, 03:38 AM)SnowLeopardFPV Wrote: That does sound to me like it's the BEC to blame then in this particular instance. I suggest you do the same test on the other board you have which powers up fine from the LiPo to see if you get 7.41V on pin 5 and the expected 5V on pin 6.

Flight Controller circuit design seems to follow a general pattern in that the 5V from the USB Port (which has already been regulated so it generally doesn't need to go through the on-board BEC) goes directly to one side of a Schottky diode and then on to power the rest of the Flight Controller.

The LiPo voltage on the other hand needs to be stepped down to 5V, so the VBAT input voltage first goes through the on-board BEC and the 5V that comes out of that then goes into the other side of the Schottky diode that the 5V line from the USB Port also goes into, and then on to power the rest of the Flight Controller.

The Schottky diode effectively acts as a one-way gate only allowing 5V from VBAT-->BEC-->5V-->Schottky-->FC-Power  OR  USB-Port(5V)-->Schottky-->FC-Power . The Schottky will prevent 5V from the USB port going back down the wire to the  BEC / VBAT, and visa versa the Schottky will prevent 5V from the BEC going back down the wire to the USB port.

It isn't a requirement to use a Schottky diode. Two separate standard silicon diodes could be used instead, however the advantage of Schottky diodes is that they have very little forward voltage drop compared to standard silicon diodes so you lose less voltage when going through them which is one reason they're generally used for this type of application.

The text diagram below is my crude attempt to try and illustrate the above description. You need to view it on a wide-ish screen otherwise the text wraps round and screws up the formatting.

Code:

USB_PORT(5V)-----------------SCHOTTKY_INPUT_1---|
                                                |---SCHOTTKY_OUTPUT------FC_5V_POWER----->
VBAT(LIPO)------BEC(5V)------SCHOTTKY_INPUT_2---|

I appreciate your help but i don't have a wide-ish screen and i'm not a circuit board tech i been watching a lot of youtube video's but this is the closest I've came when it come's to attempting to fix my FC. Does the scottky diode have two legs the one above the step down converter next to the sqaure thing with a 100 on it?

The one that comes on when the lipo battery is connected shows 6.95V on pin 6 and 7.34V on pin 5 then i connected my Multimeter to my 2S lipo battery and it reads 7.40V.

(03-Jan-2019, 10:56 AM)MicroFn Wrote: Does the scotish diode have two legs the one above the step down converter next to the sqaure thing with a 100 on it?

I replaced the text diagram in my previous post with an image of the same which won't word wrap on narrow screens.

Did you watch the video by Drone Mesh that Voodoo posted a link to earlier?

Schottky diodes have 3 legs on them - 2 legs on one side and one leg on the other. They look like the component that is directly below the large IC chip in the image which has 28 legs on it. There are only two of them on the board and they are on the same side of the board as the 5V BEC as shown in the image. Be aware that other components also share the same style 3-leg package such as transistors. So you need to trace the circuit with your multimeter to find out which one is the Schottky diode that is connected to both the 5V supply of the USB socket and also the 5V pads on the board. That will be the "gate" Scottky shown in my crude text diagram. Drone Mesh's video shows you how to find that Schottky diode on the board using a multimeter.

Thanks i did watch the video and i'm gonna watch it again and i do see those 3 legged components and i wish they were color coded but it is what it is, i'm gonna try my best to trace the circuit with my multimeter again i appreciate you guys help thanks.

I'm not sure about this because the board in the video is a Dalrc F405 and mine is a Omnibus F4 but what i did was..

i connected my 2s lipo battery to the FC and then i put the negative probe of the multimeter on ground then the red probe of the multimeter on the last pin on the USB, the pin next to the small square chip its next to the very big one with the sticker on it and my multimeter shows 5.02V.

Then i disconnected the battery i connected my positive probe to the first pin of the USB connector it's the pin above the big chip with the sticker on it then i connected the negative probe to the schottky diode the board has two of them at the bottom and on one of the two pins i get a beep, both schottky diode's give me a beep and a little battery sign also comes on my multimeter every time i checked both schottky diode's.