As many of you may know, you are locked out of using fastboot commands unless you have an engineering SPL. But I made a little discovery last night about how the HTC Rom Update Utility actually installs ROMs. Turns out it uses... fastboot!
Here's how it works:
- With phone powered on, do "adb reboot bootloader" to enter fastboot.
- -OR- With phone powered down, power on phone while holding VOL DOWN. From there press VOL UP to enter fastboot.
- Run the command "fastboot oem rebootRUU"
Now you should see a black screen with a silver HTC logo. Look familiar? This is the screen you'll see when using the RUU.
From here you can re-flash an original HTC ZIP, with "fastboot flash zip filename.zip", where filename is the name of your signed HTC image.
As an added bonus, if your phone is S-OFF (even if you're not using the ENG SPL), you can flash ANY fastboot-compatible ZIP from here, signed or not.
When you're done, "fastboot reboot" will boot the device.
Found this by accident trying to help someone on IRC who had screwed up both their ROM and recovery somehow. All they could get into was fastboot/hboot, and they were S-ON.