[EVO 4G Android Development] Bang3r:
UPDATE: With all of the newer rooting and S-Off methods, and new hardware and firmware revisions, this thread may or may not help with your specific case if trying to unroot and go back to unrooted stock. I originally wrote this based of of the very first root methods known for the Launch EVO. There is a good chance that this method will still work, but there could definitely be something unaccounted for in your own specific case, so tread with caution. It is very doubtful that anything in this tutorial will result in your EVO becoming a fancy-schmancy paperweight, but if something goes afoul, you could have a nice headache to deal with...

Ok guys. There is a lot of partial and mis-information floating around out there about how to UN ROOT if you have to send your phone back for replacement, or you want the official unrooted OTA 2.2.

OLD NEWS!!!---> NEWER METHODS AVAILABLE TO ACTUALLY FIX PRI DOWNGRADE> SEARCH!!!! EDIT your PRI to show 1.40, thanks to sturmen for the pointer, and Calkulin for the method: http://xdaforums.com/showpost.php?p=7267559&postcount=66

This assumes you are full root, S-Off. Note, this is not tested with simple root but should work (EDIT, Simple Root is basically Toastcfh's method, so you simple root users should be set), only with Toastchf's root method and nand unlock.

After reading every thread on the forum here, I think I finally found a fool proof way to do it. All the info was out there, but in several places and each one was missing something.

1) Before you start clicking and flashing and running RUUs, Check your HBoot build. You need to have the 0.76.2000 from Toastcfh's method #2. If you have 0.79.0000 (whatever) go to step 2 below. If you're getting Bootloader errors when running an RUU, I can almost guarantee that you don't have the correct HBOOT. If you somehow still have 0.76.2000 from previous modding, proceed to step 3.

2) Toast's Nand Unlock method. Found here: http://xdaforums.com/showthread.php?t=701835

EDIT: The more I think about it, I think you can just run Simple Root to re-attain the .76 HBOOT and engineering build. It would eliminate the need for any adb, and SHOULD produce the same results. Just run the RUU after you run and complete simple root. See notes in BLUE below too!

THIS STEP IS 100% NECESSARY IF YOU HAVE THE .79 HBOOT version!!!...Do step #2 in Toast's thread, just like you did when you originally unlocked NAND (OR YOU SHOULD BE ABLE TO JUST RUN SIMPLE ROOT AGAIN...UNconfirmed, but should work methinks...). Not 100% sure which steps are necessary, but I do know you need to do steps #1 (Well, #1 is Nandroid Backup, so proceed at own risk if you skip) and #2 again. Make sure after you flash the Flash_Image, and the mtd-eng through adb, that you then load the PC36IMG.zip (Engineering Build), onto the root of your SD card, and boot into HBOOT, and let it install (just like you did when rooting). I didn't bother to flash the Recovery image at the end of step 3, but I don't think it would hurt if you're nervous about losing a custom recovery image in case this method for some reason does not work. It has come to my attention that flashing the engineering build (the PC36IMG from Toast's thread)through fastboot, might be as crucial as simply having the .76 HBOOT version. It at least is a surefire way to make sure you can run an RUU on top of it. There are probably other builds/roms that will work and allow you to run the RUU, but this one is confirmed, so don't skip that step!

3) If you have the 0.76.2000 HBOOT (can be checked by powering down, and booting by holding VOL down and Power), then you can go ahead and boot into the rom, and proceed with downloading the RUUs found here: http://shipped-roms.com/shipped/Supersonic/

Go ahead and download the first one (at least). I think the others are optional to "upgrade" but why should we care. We just want to go back to unrooted stock.

4) Make sure you have the latest version of HTC Sync installed, found here: http://www.htc.com/uk/SupportViewNews.aspx?dl_id=933&news_id=627

Install, and let it do it's thing. Will probably have to restart your PC when complete. Not even 100% sure this is necessary, but it won't hurt. It's basically for the HTC drivers from what I understand.

5) Run the RUU from your pc while your evo is in the phone loaded state of the Rom, (not the bootloader) with the phone connected through USB and have HTC sync selected. Even if it doesn't connect to HTC sync on your PC, you should be ok.

If you get a USB error after the screen goes black with the HTC LOGO, don't touch the phone. Exit the RUU via the EXIT button when given the option.

6) Run the RUU again and see what happens. The Error could happen 1 more time, but just exit again, and run RUU one last time.

7) Thank everyone here at XDA that our EVOs are so badass...I'm certinly not a dev, but these devs work hard for us to have the baddest ass phone there is right now.

Any problems, let me know. I assume your errors are the same ones I was getting, and it's all because of the wrong HBOOT.

I really take no credit for this, as I'm just compiling information in a tut....