Contrary to popular belief, FW 3.71 brought a bit more than fixes to PSPEMU and the rest of the system to patch TheFlow’s Trinity exploit chain since it also changed some stuff in lv0. According to SKGleba in this Reddit thread, Sony added some checks in lv0 preventing modoru from working correctly and in order to get around them, one has to load an older ‘update_sm’ module that doesn’t have the checks included. In order to achieve this, SKGleba released dsll-mdr72 which lets you load a less secure version of the ‘update_sm’ module on FW 3.71/3.72 thereby getting past the checks Sony introduced and allowing modoru to work correctly!
Apparently, creating dsll-mdr72 was no easy feat as SKGleba ended up not sleeping in 34 hours in order to deliver a functional and tested product for the PSVita community to enjoy.

In order to downgrade your FW 3.71/3.72 PSVita or PSTV, you have to follow these steps as outlined in this PasteBin guide:

  1. First, you need to download a few files (links included in PasteBin guide) in order to get you started which include:
    • The FW 3.65 and FW 3.72 PUP filesDowngrading from FW 3.71/3.72 is pretty easy and only requires you to do a little work in order to make modoru work properly!

    • Modoru
    • dsll-mdr72
    • A decrypted version of FW 3.65’s ‘update_sm’ lv0 module

  2. Make sure you’ve run h-encore˛ to enable homebrew loading
  3. Copy the FW 3.65 PUP file to ‘ux0:app/MODORU000/PSP2UPDAT.PUP’ and the FW 3.72 PUP file to ‘ux0:data/PSP2/UPDATE/PSP2UPDAT.PUP’
  4. Place the decrypted ‘update_sm’ module you downloaded in ‘ux0:data/update_sm.bin’
  5. Install Modoru’s and dsll-mdr72’s VPK on your PSVita via VitaShell
  6. Restart your PSVita and run h-encore˛ to re-enable homebrew
  7. Open the ‘decsecldr[LITE]’ bubble (i.e dsll-mdr72), wait until it says ‘Module Loaded’ and then press ‘START’ to exit
    • As the application’s success rate is around 25%, the application may crash or hang, if these happen do a force restart by holding the power button after 30 seconds of nothing happening

  8. After the above step is successful, it’s recommended to make sure that the module loading was stable by opening some apps such as the ‘Settings’ and ‘Welcome Park’ apps
  9. Open modoru and downgrade as normal
    • If you get a long floating bubble before Modoru starts , reboot your device and repeat from step 7
    • If the downgrade process crashes, reboot to safe mode by pressing ‘PS (PS button) +RT (Right Trigger)+POWER’ and navigate to ‘update system firmware->update from vita memory card’ in order to reinstall FW 3.72 and try again

  10. Enjoy your FW 3.65 PSVita and remember to install HENkaku Ensō!

While the guide is specific to FW 3.65, you can easily use it to downgrade to another FW by substituting the FW 3.65 PUP file with another one like FW 3.60’s PUP file for example. A full list of PUP files can be found here – make sure to download the ones in the ‘Complete Official Firmwares’ section!