For anyone who has a Happymodel EPx ExpressLRS receiver, be aware that some of them have a hardware defect which can cause the 5V regulator to burn out. Not all receivers are affected, but the ones that are have the marking "SDG" on the ESP receiver chip.

The ExpressLRS devs are proposing to implement a software fix to eliminate the problem by skipping RF calibration at start-up on these receivers which is what triggers the issue, but this is less than ideal and is really just a kludge to get around the hardware defect. The real fix is to replace the onboard 150mA 5V regulator chip with one that can supply 500mA of current, or to modify the circuit so that 3.3V is supplied to one of the input legs of the 5V regulator.

Happymodel have now apparently rectified the issue on newer batches of their EPx receivers so if you find that you have one of the affected receivers then the best course of action would be to contact the vendor you bought it from (or Happymodel themselves) and ask for a replacement EPx receiver under warranty.

A detailed description of the issue can be found in pull request #928 of the ExpressLRS GitHub page.

Thanks! I will check my RX, I have 3 RX in quads and 2 RX on their way today or tomorrow..

For reference, this is what you're looking for on your EPx receivers. If the chip on the top left says "SDG" like here, your receiver is affected and you should try to get a replacement or at least run the new patched firmware to help mitigate the issue. 
   
Credit to Hofa on ELRS Discord for the image. Luckily none of mine are affected.

Thanks V-22
I really needed to see that picture to figure it out.
I have an EP1 and a EP2 both are unaffected as well.


Scott

One of my 3 Happy Model receivers has the LDO regulator with SMD mark SDG. Coincidentally, this is a receiver that I only tested for 2 days and was ready for another project. The test ran at a power of 100 mW and throughout the testing I did not notice a single problem, firmware was updated to v.1.0.0 prior testing.
This piece of receiver, along with other components, was purchased at Banggood. Has anyone asked Banggood for a replacement of receiver with this SDG LDO?

From what I understand, the 5V regulator may not burn out immediately but can burn out over time, and the last thing you want is for any damage that might have been done to it to suddenly surface when your quad is a few kilometres out. I certainly wouldn't be using one of the affected receivers without the firmware patch applied, and even then I would probably still be a little nervous. Best to just replace it with a known good one at the earliest opportunity.

If BG aren't aware of the issue and/or Happymodel haven't informed them then you might struggle to get them to understand what the issues is and for them to send you out a replacement, but you have nothing to lose by contacting their customer support.