[Acer Iconia A500] drkalo:
Well as long as we have ICS OTA this thread seems to be less needed. Anyway, I'll leave it this way in case someone is stuck on HC 3.2 without root and without being able to update to ICS. How to get root on your stock ICS, look here or here

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If you’re reading this may be you’re stuck with a 3.2 OTA update without ROOT privileges on your A500. This tutorial explains how to revert your OTA 3.2 to 3.0.1. Original article for those of you who speak Russian here

Thanks to begemot666.

These methods could be used to unbrick your device i.e. when boot.img and recovery.img are corrupt.

METHOD 1 - thanks, vache

It is best to use a PC with Windows 7 on it. Most of the problems reported seem to be XP related.

1. Download and unpack the archive provided by vache here - for Firefox rightclick and select "Save link as".

MIRROR

2. Get your UID (without it nothing is going to work). How to do that – read sc2k’s itsmagic thread. Enable USB debugging on the tablet.

3. Edit the file CPUID inside the extracted folder with a text editor - you have to change this line with your UID number but you need to add “zeroxzero” in front of it, example: if your UID is 37c7040425ff0d7, at the end it needs to look like 0x037c7040425ff0d7.

Save the file.

4. Connect your tablet with the PC.

5. Run PBJ20upgrade.exe as administrator and follow app instructions. USB drivers are provided with this archive and the app installs them automatically according to your system.

6. After driver installation the app scans your tablet and it will show version number of your current firmware and version number of the firmware that is going to be applied after restoration. Follow all application instructions. Tablet will switch to APX mode with ACER logo on its screen and on your PC you’ll see the progress bar of the process. Before the beginning of the flashing process the app will ask you for identification number. Here you enter your UID which you have placed in the CPUID file with a zero infront. Example: 037c7040425ff0d7

Below are screenshots from the EUU app that's used to downgrade to 3.0.1

The whole things takes 10 or more minutes so be patient. Then you’ll have HC 3.0.1 :D

All data on your system and data partitions will be lost. Storage will remain intact.

7. Once on Honeycomb 3.0.1, install Iconiaroot 1.3, root your tab and then install CWM from thor's site (there you can find the latest version) or use Acer Recovery Installer from the Market, or look at the original thread here

8. Boot into CWM and flash whatever ROM you like!

METHOD 1 update:

You can use timmyDean 's modified and tweaked EUU tool that will flash directly a rooted stock 3.2.1 ROM:

http://xdaforums.com/showthread.php?t=1307539

METHOD 2 - thanks GamezR2EZ

This is even easier because it does not need your UID. It is just flashing as a normal update but actually it is an older HC version that is rootable by Iconiaroot. Additionally method 2 leaves your data intact and you will be able to backup your apps after downgrading with tools like Titanium Backup. Thanks heldc for pointing this out.

1. Download this package (named "downgrade not stable"). mirror1 mirror2 mirror3

2. Extract the update.zip from it and place it on your external SD card.

3. Turn off your tab and then turn it back on while holding Volume Down key. This will automatically flash the update.zip from your SD card.

4. After flashing is finished you'll have unstable Honeycomb 3.0.1 - gives errors and crashes but you only need it to root and install CWM. If it fails to boot try to hard reset your device *.

5. Install Iconiaroot 1.3, root your tab and then install CWM from thor's site (there you can find the latest version) or use Acer Recovery Installer from the Market, or look at the original thread here

6. Boot into CWM and flash whatever ROM you like!

GOOD LUCK !

* How to hard reset your Iconia A500

1. Turn off your tablet

2. Place the screen lock button on the left (red not visible)

3. Hold Volume UP + Power button

4. After the vibration, release the power button and toggle the screen switch few times left-right until you see the following lines appear on the screen

Erasing Userdata...

Erasing Cache...

You can now release Volume UP button.

5. In the top left corner you'll see formatting has started.

6. Tablet will reboot