Although we now have Flash Image GUI to flash kernels on rooted HTC EVO 3Ds that are locked on S-ON, there may come a time when we need to flash a ROM or kernel that's misbehaving from recovery mode due to a massive system crash and lack of proper Nandroid backups.
You've probably heard the quick and dirty statement when something does not flash properly to "just flash it from fastboot," but what exactly that entails is usually not included.
If you've unlocked your NAND/bootloader by visiting HTCdev.com and going through their process, you have been left with a device in NAND-unlocked/S-ON state. What this means is you can write ROMs that use stock kernels pretty normally, but attempting to flash kernels, ROMs with custom kernels, and a few other things will look like it works but will never stick properly. You'll flash a kernel or a ROM but the result will be an unstable WiFi-less mess running the stock kernel.
For recovery to work as it used to in the good ol' EVO 4G days (or for anyone lucky enough to have a 3D with S-OFF), you need to have a couple of programs and a computer. As I only have access to a Windows box for the next few days, what follows is going to be Windows-centric.
You'll need ADB, fastboot, and a recovery image.
Although I would normally suggest familiarizing yourself with ADB, we'll do this a rather quick and dirty way.
1. Download just the basic HBOOT 1.50 tools here, which you might want to get before attempting the HTCdev steps above, and skip the several hundred meg install of the Android SDK. The link includes an old working recovery, but you can also download a newer recovery image if you want. Make sure to download the image, not the .zip, and place it in the c:htcroot directory.
2. Unzip the basic tools somewhere you'll be able to get to it easily on your computer. For purposes of this piece, we'll extract that to c:htcroot and plug in your EVO 3D (USB debugging on, charge only).
3. Open a command prompt on your computer.
4. Type cdhtcroot and press enter.
5. Type adb reboot bootloader and press enter.
6. After your phone boots into the bootloader type fastboot boot cwm-184.108.40.206-shooter.img and press enter
This "normal" recovery will last only until you exit and reboot your EVO.
Without a computer to execute those commands, you will not be able to write normally and will be stuck with S-ON issues. You can still make Nandroids and do a lot of things the cool kids do, though.
Until we get S-OFF for HBOOT 1.50, we will have to rely on a computer or Flash Image GUI to place the EVO 3D into a fully-flashable state. And don't forget that Flash Image GUI can only be run if your phone can boot up.
As a note, it does not matter what recovery you have flashed on your phone. Booting the recovery image via this method does not write the recovery to the phone. What this means is that if you have TWRP installed and follow the above commands, you'll boot into ClockworkMod (CWM) but after the phone resets, there won't be a trace of CWM left.