Public Service Announcement:
So, this happened to a bunch of BetaFPV F3 FCs recently. I have reported this to the manufacturer and they said they will fix it in the next revision. This is also known to happen to other FCs, because the problem is based on a popular way of setting up the power supply across the board.
Its one if these issues that appear intermittently, create different symptoms, and are caused by various reasons. Most annoying problems to have!
The problem is that the receiver on the board stops working completely. Or it is unreliable. Takes a few tries to bind, then looses connection randomly. Or the receiver only works when the board is powered over USB, but not when powered over the battery.
After examining a few broken boards, we conclude that a blown voltage regulator is the cause for all these issues.
Why do you need a voltage regulator?
Some components only work good at a very constant voltage. A receiver usually needs very precise 3.3V. Since the input voltage from a battery changes a lot depending on load and charge condition, we need to regulate the voltage. Voltage regulators are often rectangular black components with 4-6 legs. They smell funny when you apply reverse voltage.
How can you blow up a voltage regulator?
There are three popular methods:
1. Just connect a battery in reverse. That will reliably kill the regulator completely.
2. Solder the camera connections to the wrong pads. Upon applying power, that might dump so much current through the cams signal input that cam and voltage regulator go boom.
3. Power the board from USB and battery. We cannot 100% confirm this, but it seems to damage the voltage regulator in some cases.
1. TRIPLE-CHECK polarity!!
2. TRIPLE-CHECK polarity!!
3. only ever use ONE powers source!!
and bonus lesson: damage is not always obvious immediately..
Here is an article on the betaFPV forum with more details and info how to replace a blown voltage regulator: https://betafpv.freshdesk.com/support/solutions/articles/27000021324-troubleshooting-battery-polarity-reserved-connection