first of all: i successfully downgraded my iPhone 3G from a jailbreaked (with pwnage tool 4.01) 4.1 firmware to a original 4.0.1 firmware i downloaded from [http://www.hackint0sh.org/f127/22056.htm without the existence of any other saved SHSH hashes/blobs/whatever than the 4.1 ones!
a short history of my tragedy:
I am an iPhone noob and have little experience on jailbreaking my device since i bought it "years ago". Last week i got an iPhone 3G from a friend with a "gray no wifi" error (maybe you heard about this!?) and he asked me to solve the problem (lol).
At this time there was the firmware version 4.0.2 on the phone and it didn't boot up any more. Only the (pine-)apple appears and noting else happened. So i upgraded the firmware to the jailbreaked 4.1 version but the "no wifi" error still was there and it seemed to be a dead end because all other possible solutions mentioned much earlier firmware versions to work with.
I downloaded several tools and read the entire internet to find a way to downgrade from 4.1 to ... whatever. iTunes always refused the downgrades with a "3002 error" even with TinyUmbrella, a program that should start a TSS Server to bypass the version check (???). But: i used Umbrella to save the current SHSHs to the cydia server. I also checked if there are other SHSH versions saved - but 4.1 was now the only one
the things i did to downgrade:
1) i downloaded blackra1n by geohot RC3 (for windows - on a XP SP3 machine)
2) at startup a missing ASL.dll error appeared so i copied the .exe file to the "Apple Application Support" folder where the .dll is located.
3) i started blackra1n again and hit the "make it ra1n" button: "waiting for device" appeared
4) i connected the iPhone to the computer and iTunes started automatically (with an error message)
5) i closed iTunes while a man with a speech bubble appeared on the iPhone screen with "npebea" in russian letters!?
5) after a while (about 5 minutes) nothing else happened so i closed blackra1n - the npebea man was still on the phone screen!
6) i started iTunes and got the message, that a iPhone in service mode is connected
7) i chosed shift+upgrade and selected the 4.0.1 firmware and ... no errors!
There IS the 4.0.1 firmware on the iPhone!!! and everything is working fine (except the "gray no wifi" problem)
iPhone 3G with a jailbreaked 4.1 firmware using this howto
Windows XP professional SP3
iTunes 10.0.0.68 for Windows
blackra1n by geohot RC3 from here
and the original 4.0.1 firmware to downgrade
here it is: the iPhone running 4.0.1 with the 4.1 saved SHSHs
can anyone else verify this procedure???