I am getting ready to upgrade the trusty LaForge module in my Fat Shark Dominator v3’s to the new ImmersionRC RapidFIRE. While looking over the manual for the RapidFIRE module, I noticed that it says older goggles (mine included), do not supply enough power through the module interface. An option is given to the installer to perform a mod on the Fat Shark module PCB or to obtain a power from the head tracking & power board on the right side of the goggles. Since I had some spare time and was curious, I decided to mod the PCB in my goggles. I’ll outline the procedures for doing the mod in this article.
Why Mod Your PCB?
Older FatShark goggles, which include almost every Dominator-branded goggle that are not the HDO’s, provide power to attached modules through a filtered circuit which includes an inductor that pulls down the voltage levels when high current is demanded. This lowered voltage is a result of the inductor doing too much work and continued operation will potentially result in it burning out altogether. This type of high-current demand is exactly what is required by the new ImmersionRC RapidFIRE RX module. The inductor in question is also well known to burn out in Fat Shark goggles under “normal” loads by other RX modules.
Fortunately, the inductor can be removed entirely from the PCB without any issues. This is because most quality RX modules contain internal power filters which perform the same job and have circuit components which are properly sized for their usage.
This is a long way of saying there are three reasons you might want to perform this mod:
- You are installing the ImmersionRC RapidFIRE RX module in a pre-2017 model of Fat Shark goggles.
- Your L1 inductor burned out during normal usage with your goggles and you want to get them working again.
- You are having power issues with your RX modules, which can include brownouts or diversity modules not working.
What’s Required for the Mod?
Mainly killer soldering skills. You do not want to attempt this modification unless you are quite confident in your ability to solder to small PCB components. If you have successfully built 2 or more quadcopters without any major electrical issues, you probably have the skills needed. You may still want to practice soldering to PCB components on scrap electronics you might have handy. You will want a good soldering iron with a fine-pointed tip. You will also need some thin, high-gauge wire. This wire can be harvested from pretty much anywhere – I got mine from some spare connector wire that came with one of my flight controllers.
This mod requires a decent amount of expertise and skill to pull off. Screwing it up could mean permanently damaging your $500 Fat Shark goggles. If you are not confident in your soldering skills I recommend you look elsewhere to solve one of the above problems, or send your goggles to a professional. We are not responsible for what you do to your own equipment, even when following our guides. Mod at your own risk.
First off, you’ll want to split your goggles. This starts by removing the faceplate, which is accomplished by removing the black screw circled in red below:
And firmly pulling the faceplate away from the goggles. Several plastic tabs lock the faceplate in place, so it may help to twist the edges a bit to unlock the tabs. After removing the faceplate, remove the goggle strap by feeding it through the slots on each side of the goggles.
Next, you’ll remove the screws on the bottom of the goggles, circled below:
This will allow you to split the goggles in half. This procedure can be complicated if you don’t know what you’re doing. However, if you squeeze the plastic near the upper part of the nose ridge and the back of the goggles, I’ve found that the two halves pop apart easily. Note that in the below picture, the goggles are being held upside down:
Now yo uwill be free to access the module PCB inside of the goggles. It is attached to the rest of the goggles with a delicate ribbon cable. Carefully pull the plastic grey/black tab where the cable attaches to the PCB out to release the cable. Be careful here! These tabs break easily and will be very hard to replace.
Once the ribbon cable is removed, you will be able to take out the module PCB. The ribbon connector in the picture below is in the lower left hand corner.
Now that we’ve extracted the part we’ll be modding, let’s get into the procedure itself. It’s actually quite simple: you’ll be bypassing the inductor labelled “L1” on the PCB with a simple wire. This inductor is apparently under-rated for modules with higher power draws and thus causes problems. We are fortunate that the power-filtering provided by this inductor is not necessary with most well-designed modules, so it can simply be bypassed. Bypassing can be performed by removing the inductor and creating a solder bridge, or by adding a shunt wire. The latter solution is easier to do and easier to remove if you ever decide to return your goggles to “stock” form. For these reasons, this is the way I will approach the problem.
First, you’ll need to identify where your L1 inductor is located. These PCBs have gone through several revisions and the L1 inductor seems to have changed places in each revision. Fortunately, it is always labeled. On mine, it is placed just behind the switch in the lower right hand corner of the picture above. I have heard many reports that others have found their L1 inductor on the backside of the PCB. Just put your PCB under the microscope and find the element labelled “L1”.
Next, you’ll build your shunt. I used a small segment of silicone wire, with each end exposed and pre-tinned:
Make sure the exposed ends of your wires are as small as possible. You do not want to short multiple circuit elements together.
If you have a sufficiently thin soldering tip, it should then be trivial to solder each wire end to each side of the inductor on the circuit. Again – pay special attention that you do not short the inductor pads to any of the other circuit elements on the PCB. Here is my shunt installed:
With the shunt installed, you just need to reverse all the above steps to re-insert the module PCB and put your goggles back together. If you have a RapidFIRE module, you can test whether or not your mod works by going to the settings menu and verifying that “power mode” is “ON”.
A special thanks to the ImmersionRC RapidFIRE manual and YouTube user FlightClub for providing reference material for this article. Please check out FlightClub’s videos to see this mod being performed live: