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Acer (Chromebook) - C740

This repo is far from done, it can be updated any time.

This repository is created for To share with me knowledge and everything is done for educational purposes. I take no responsibility whatsoever over other users' responsibility and I urge no one to use these methods to bypass and remotely lock the chromebook.

All pictures is from my Google Pixel 4 device, got few q about that robot

Screenshot Screenshot

Unbrick a bad flash

Bypass a remote locked Chromebook (Acer C740) wich will be my device for show and give you examples, it works same for all laptops no matter what sytem you run.

I always want to find out what's going on on the other side and not only know how to get things done but because I love learning new things and then I need to know how it goes when locking a chromebook as an administrator, so if if you want to learn more, you can create a Google Admin account that costs some money, but it's worth it, so you do not have to speculate about what your chef / teacher can see, but I will not address that here and now. until later. A chromebook that is first via the remote control and leaves a message on the screen that the device should te.x return to X and on the phone number X so the serial number must be changed, this is how they lock the device and it is possible to get past by flashing bios with a new rom. For this you need three things.

  1. Bios Programmer (I use ch341a myself)

  2. One 8 soic clip (recommended: don't buy a cheap one, they will last 1-3 times then you wont be able to attach the clipper again and it is annoying something extreme so go for a 3M one)

  3. A new rom (this can be found on variou places online)

Either you can buy a fixed clip or you can connect cables as I do in the banner.

A pre-fixed clip + contact (price for this is usually ~1€->3€, you can get over them cheaper but in avg this is the price) 8_soic_clip-done

A custom made clip if you are really poor you can get a clip from ~0.1$ Screenshot

How should i place pins?

Screenshot Screenshot

CH341 as a programmer OR a reader

From store, you will get a jumper for pins, hence my own jump on the picture but when 1&2 are bracked the device is conifgured as a programmer:

Screenshot

If you remove the jumper the ch341 is a serial console reader, as a TTL Serial Converter (ftdi rs232, for example) adapter:

Screenshot

The dot i marked is were the VOLTAGE should be, this is really really important otherwise your ship may burn: Screenshot

Flashing

First we need flashrom, install as below:

  • Gentoo:
emerge --ask flashrom
  • Ubuntu/Debian/Kali/Mint:
apt-get install flashrom
  • MrChromebox:
wget https://mrchromebox.tech/files/util/flashrom_20200918.tar.gz && tar -zxf flashrom_20200918.tar.gz

Test connectivity and ensure the flash chip is properly identified:

flashrom -p ch341a_spi

Extract old BIOS:

flashrom -p ch341a_spi -r old_bios.rom

Write new BIOS:

  • It's really important to wait until whole process is done, it will also VERIFY the new bios
flashrom -p ch341a_spi -w new_bios.rom
  • Thats it :)

ChromeOS Hacking

Change serial/service number/tag

vpd -i RO_VPD -s serial_number=xxxxxxx" (xxxxxxx is the Service Tag of the system
  • Verify that things has been written:
vpd -l

Misc:

We are not allowed to browse mrchromebox archive site but after some digging I found 'cbmodels.json' and from here we can get all files (sorry if you don't like this), so with below command you can download all roms from mrchromebox wiki (they all are stored under roms)

curl -sL https://nr1.nu/archive/chromebook/misc/cbmodels.json|grep -Eo '(http|https)://[^/"].*rom'| xargs wget -q --show-progress

Also available from:

https://github.com/wuseman/Acer_Chromebook-C740/tree/main/roms

Firmware Sources for Google ChromeOS

GREP latest firmwares for your chromebook model (grunt in this example):

elinks -dump https://cros-updates-serving.appspot.com/|grep -i grun |cut -d' ' -f3|xargs wget -q --show-progress

Requirements

A chromebook device, soic 8 clip and a ch341 eeprom/bios reader

Web

Visit my websites and profiles for the latest info and updated tools

https://github.com/wuseman/ && https://nr1.nu && https://stackoverflow.com/users/9887151/wuseman