FrSky D4FR 1st batch PPM timing issue

Hello,

I did not want to make this information public until I received and confirmed a fixed version from FrSky. First batch of the D4FR receivers sold by HiModel and perhaps other places had a bug where the CPPM (not sure about individual channel output as that doesn't interest me) output was offset by as much as 40us requiring substantial trims to get center stick points to 1500us.

I contacted FrSky and they were very helpful and acknowledged the issue, and said were working on a fix. A day later I was informed this was fixed, but because D4FR is not user-firmware-upgradeble, I was told they'd ship me a new unit for review, which they did. It arrived today and I can confirm the issue has been fixed.

Here's some scope screenshots of PPM output to show the bug. On my Turnigy 9X with DJT module I had to trim almost 80% in order to correct the channels with original module.

D4FR trimmed (not optimal, this is the problem)


D4FR untrimmed (this shows the offset from 1500us)


For comparison, here's D8R untrimmed


Here's radio's PPM output from trainer port


And, here's the fixed D4FR I just got in the mail today:


Everything is good.
So, if any of you were 'early adopters' of D4FR and noticed that you need substantial trim in order to zero channels from CPPM output, you might want to contact FrSky and get them swapped/upgraded. Don't ask me how to do it, but I just emailed their support4tech email.