The ZTE Obsidian (model Z820) is a compact, entry-level 4G LTE smartphone from 2015, primarily offered by the T-Mobile network in the USA. It’s designed for basic smartphone functionality, featuring a 4.5-inch display and powered by a MediaTek MT6735M processor. This guide provides the official stock ROM, which is essential for unbricking the device, fixing software bugs, removing a Google FRP lock, or restoring the phone to its original T-Mobile software.
Important: This firmware is specifically for the ZTE Obsidian (Z820). As a MediaTek device, it requires the SP Flash Tool for flashing. Flashing this on a different model will cause a hard brick. This process will erase all data on your device.
Quick Device Specs
- Device: ZTE Obsidian (Z820)
- Release year: 2015
- Chipset: MediaTek MT6735M
- Display: 4.5″ TFT Display
- Battery: 1800 mAh
- Original OS: Android 5.1 Lollipop
Required Downloads
To flash a MediaTek device, you will need the specific drivers and flashing tool. You can find the downloads for these in our main guide linked below.
- SP Flash Tool
- MediaTek VCOM USB Drivers
Stock ROM (Firmware)
| Region / Carrier | Android | Type | Download | Chipset |
|---|---|---|---|---|
| USA (T-Mobile) | 5.1 | SP Flash Tool Firmware | Download | MediaTek |
How to Flash the Stock Firmware
Flashing the stock ROM onto your ZTE Obsidian requires a Windows PC and the SP Flash Tool. The process involves installing the MediaTek VCOM drivers, loading the MT6735M_Android_scatter.txt file from the firmware into the tool, and then connecting your powered-off phone to start the flash. This will completely restore your device to its original T-Mobile software.
For detailed, step-by-step instructions with screenshots and tool download links, please follow our comprehensive pillar guide: How to Flash Firmware with SP Flash Tool.
Device-Specific Troubleshooting for ZTE Obsidian (Z820)
- Correct Driver Installation: The most common failure point is incorrect drivers. If the tool doesn’t see your phone, you must install the MediaTek VCOM drivers, which often requires you to disable ‘Driver Signature Enforcement’ in Windows first.
- Using the “Boot Key”: To initiate the flash, power the phone off completely. Press and hold the Volume Down button, and while holding it, connect the phone to your PC. The tool should then detect it and begin the process. If Volume Down doesn’t work, try holding Volume Up.
- Fixing Google FRP Lock: If you’re locked out of your phone by Google’s Factory Reset Protection (FRP), flashing this stock ROM will perform a complete wipe and remove the locked account.
- T-Mobile Carrier Firmware: This is an official ROM for the T-Mobile USA network. It will restore all T-Mobile branding and pre-installed applications. It will not remove the SIM lock; your device will still be locked to the T-Mobile network after flashing.
FAQs
Q1. My phone is very slow and apps keep crashing. Will this fix it?
Yes. For a device with basic hardware like the ZTE Obsidian, a clean flash of the stock ROM is the best remedy for age-related software slowdowns and frequent app crashes by restoring the operating system to a clean, factory state.
Q2. Can I upgrade this phone to a newer Android version like Marshmallow or Nougat?
No. This device’s official support ended with Android 5.1 Lollipop. Due to its basic hardware and MediaTek chipset, a custom ROM community for it is virtually non-existent, so no unofficial upgrades are available either.
Q3. Will this unlock my phone from the T-Mobile network?
No. Flashing the official carrier firmware will restore the phone’s software, but it will not remove the SIM/network lock. The device will remain locked to T-Mobile.
Q4. What is a “scatter file”?
The scatter file (e.g., MT6735M_Android_scatter.txt) is a crucial map for MediaTek firmware. It tells SP Flash Tool the name, size, and location of every partition on the device’s storage, ensuring each part of the software is flashed to the correct place.
