A) Things to know about your iPad:
1. iPad previously jailbroken, and with SHSH on file with Cydia for at least 4.2.1 and 4.2b3
Cydia MUST have your 4.2b3 SHSH for this method to work.
2. Willingness to lose your app settings as you should set up your iPad as new device to avoid potential problems
(However, there are a few apps in Cydia to save those data, and restore them manually later if you know how to)
3. A Macintosh computer (Sorry no Windows version of redsn0w yet)
B) Gathering Files:
1. Download the current iOS 4.2.1 ipsw file from Apple – iPad1,1_4.2.1_8C148_Restore
2. Download redsn0w_mac_0.9.7b6 from iPhone Dev Team
3. Download iPad1,1_4.2_8C5115c_Restore.ipsw (google for link)
4. Download Pwnage Tool from http://blog.iphone-dev.org/
I used PwnageTool 4.1.3 Unlock Edition – PwnageTool_4.1.3_Unlock_Edition.dmg
5. Download TinyUmbrella (ver 4.21.05)
1. Install TinyUmbrella, and launch the app with your iPad attached to Mac
2. Click "Save SHSH" to get all files available from Cydia.
3. Now go to the Advance Tab. Leave "Set Hosts to Cydia on Exit" as checked
(Uncheck this in the future when you want a clean restore from Apple)
D) Put your iPad in DFU mode and Restore to a fresh copy of iOS 4.2.1
1. Unzip PwnageTool_4.1.3_Unlock_Edition.dmg, move the pineapple icon to your desktop (or in Application folder) and run it.
2. Select the iPad, so there is a green check mark beside it.
3. Click the DFU icon, and follow the instruction
4. It will confirm when your iPad is in DFU
5. Go to iTunes, hold OPTION button on keyboard and click Restore.
6. Select the iPad1,1_4.2.1_8C148_Restore you downloaded
7. After iPad started, leave connected to iTunes so it would activate.
(Stop here, don’t set up your iPad with iTunes)
E) The jailbreak:
1. Unzip the redsn0w, and drag the folder or the pineapple icon to desktop and launch it.
2. Click browse and point it to your iPad1,1_4.2.1_8C148_Restore.ipsw
3. Go Next, then select both "Install Cydia" and "Jailbreak Monte"
4. Now point it to your iPad1,1_4.2_8C5115c_Restore.ipsw
5. Next, and read the instruction carefully (It instruct you to bring your iPad to DFU again)
6. Follow the steps (timing is very important). If you mess up, just click ‘back’, and start over.
7. When your iPad enters DFU, it app will do its job to jailbreak it.
8. Hopefully everything will go well, it’ll restart, and you are DONE!
F) My Result
It appears to be working flawlessly, just as it was with iOS 3.2. No problem with bluetooth or dropping wifi signals. From Cydia, I installed RetinaPad, Activator, Display Out, and FAkeClockUp, and they are working great. Multitasking working nicely. Airprint is working after I installed Airprint Activator (free) on my Mac.