[SOLVED] I'm looking for G-BEST M20 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my G-BEST M20. It's started acting up, and I'm looking for a detailed service manual with boardviews and schematics to properly diagnose and repair it. I need to take precise voltage measurements around the board, so having the right documentation would be very helpful.

Thanks in advance for your help.

Selected Answer

I actually found that service manual on a tech Discord server a while back. A really helpful member there shared a direct link to their blog and I've saved it. I'm happy to pass it along here. Hopefully, these boardviews and schematics help you fix your phone, just like they got me through my repair. Looks like we have the same model.

@Frederic

Absolute legend! That's exactly the info I was searching for. This is going to save me so much time probing in the dark. Seriously, thanks a ton for sharing the link!

Hi there,

I also have the G-BEST M20 and just downloaded the manual you shared. I'm pretty new to board-level phone repair, and this is a bit intimidating with all the tiny test points and the schematics. Could you point me in the right direction on how to start troubleshooting this ? Any advice on the first few things I should check would be a massive help.

Thanks so much for your time

General advices: start by checking the voltage at the battery connector on the board. With a known-good battery connected, you should see a steady voltage between 3.7V and 4.2V. After that, a great next step is to check the main power management IC (PMIC) for shorts. Using your multimeter in diode mode, check for shorts on the large input capacitors surrounding the PMIC.

Here are a few useful references for troubleshooting your device:
https://xdaforums.com/t/htc-evo-4g-themes.1316295/
Take a look at comment #1546
Also, this : https://www.ifixit.com/Answers/View/313440/What+board+should+I+use+for+replacement.
You can also check this video starting from minute 1:

The G-BEST M20 service manual and boardviews from the link above were exactly what I've been searching for. I couldn't find a complete, free copy anywhere else. Seriously, thank you for sharing this you're a lifesaver!

Hi everyone, I'm working on a G-BEST M20 with a no power issue and need some guidance with my measurements.
I'm detecting 3.3V on the VREG_MAIN line (pin 1 of the PMIC), which looks good, but I'm getting 0V on the VDD_CPU line (pin 8) where the schematics indicate I should see about 0.9V.
Since this is a core voltage for the application processor, could this missing rail be why the device shows no signs of life?
What's the best procedure to diagnose this further? Should I check for shorts on the CPU rail first, or look at the PMIC's enable signals?
I've already verified the main 3.3V and 1.8V power rails are present and stable.

My G-BEST M20 was working perfectly until yesterday when it suddenly went completely dead. Now it won't respond to the power button, doesn't vibrate, and shows no signs of life even when connected to a charger. I'm worried there might be a serious issue.

I have a decent multimeter, a basic soldering iron, and a healthy dose of patience. While I've successfully replaced iPhone batteries and charging ports, this will be my first attempt at actual diagnosis. The sheer density of BGA chips and microscopic components is honestly a bit overwhelming.

I'm particularly curious about the alcohol trick I've seen online where you apply isopropyl to the board and look for evaporation hotspots to locate shorts. Is this actually a reliable method for beginners, or are there better approaches I should try first with just a multimeter?

I learned this lesson the hard way last month with mine, it was declared "dead" by two different shops. The phone showed absolutely no signs of life - no charging indicator, no vibration, nothing. Before diving into complex board work, I decided to try one more basic test: wireless charging.

To my complete surprise, it actually heated up on the charging pad! This single discovery completely changed my diagnostic path. It turned out the issue wasn't with the main board or processor, but with the notoriously fragile USB-C port that had failed completely. A $15 replacement part and some careful soldering brought it back to life.

The moral? Always exhaust every external testing method before opening the device. Test wireless charging if available, try different charging methods, and don't assume the worst case scenario. Sometimes the most "dead" devices have the simplest solutions hiding in plain sight.

I suspect my issue might be related to that cheap, third-party fast charger I used at the airport last week... Now the device gets extremely hot during charging, the screen flickers at low brightness, and sometimes it randomly shuts down at 30% battery. Could this have damaged the power management IC or battery calibration?

If your G-BEST M20 starts acting up, random reboots, fast battery drain, or connectivity issues, there are several diagnostic steps you can take before assuming the worst:

• Check your charging habits: Using poor-quality chargers or wireless pads can gradually damage your battery and charging circuit, leading to unpredictable behavior.
• Inspect the physical components: A slightly damaged charging port, worn battery, or even accumulated pocket lint can cause issues that seem like major hardware failures.
• Monitor temperature patterns: If your phone gets unusually hot during specific tasks (like camera use or gaming), it could point to a failing component rather than a software issue.
• Use diagnostic tools wisely: Ampere for battery health, phone diagnostic codes (*#0*# on many models), and a thermal camera can reveal problems without opening the device.
• Know when to stop: If you see liquid damage indicators tripped or smell burnt electronics, it's time to consult a professional before causing irreversible damage.

Also visit this link it may help : https://xdaforums.com/t/usb-host.1530192/

Here's what I discovered on forums and technical databases:

Repairing a damaged RF shield can range from a relatively straightforward mechanical fix to an advanced micro-soldering challenge. Back Cover Removal: Most modern smartphones are designed with a glass back cover secured by adhesive. Then, use a flashlight and a magnifying glass to meticulously inspect all microphone holes for lint, dust, grime, dried liquid, or any other foreign material. Understanding the symptoms associated with connector wear helps in targeted inspection. If only one specific device experiences issues, the problem might be with that device's Wi-Fi adapter or software, not the hotspot itself. iPhone: Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings. Improper Repair Attempts: If a device has been opened for repair, using incorrect type/quantity of adhesive, failing to properly clean old adhesive residues, or not allowing new adhesive sufficient curing time can lead to premature adhesive failure. ADB and Fastboot Drivers: For your PC to communicate with the phone in Fastboot, the correct Android Debug Bridge (ADB) and Fastboot drivers must be installed. If it's always the same color (e.g., always green on a black, red, or blue background), it's stuck. If input voltage is present but output is not, the boost converter (IC, coil, diode) is likely faulty. If any issues, power off, disconnect battery, and recheck connections. Water Damage: Liquid ingress can corrode internal components, including the digitizer's connectors, causing erratic behavior. Short to Ground: A very low reading (close to 0V) on a power or data line indicates a short circuit. Charge Your iPhone: Ensure your iPhone has at least a 50% charge to prevent it from dying during the restoration process. Carefully align the new screen with the frame and gently press it down around the perimeter to engage the adhesive and any clips. It's distinct from a "No SIM card detected" error, which usually points to a physical issue with the SIM card or the tray. Inspecting smartphone camera OIS mechanisms is a highly technical procedure that demands precision, specialized tools, and a thorough understanding of micro-electronics. Replacing a speaker mesh fabric is a relatively minor repair in the grand scheme of smartphone fixes, but it's one that significantly impacts audio quality and protection. When a touchscreen becomes unresponsive, exhibits "ghost touches," or has dead zones, it renders the device partially or completely unusable. Usually, this involves removing a small metal shield with Tri-point screws, then prying up the flex connector. Ultra-Thin Metal Prying Tool or Guitar Picks (use with extreme caution): Only if absolutely necessary for initial separation, but plastic is preferred. Restart the Device: A simple reboot can often clear temporary software glitches that might be preventing the vibration motor driver from activating. Within the intricate confines of a smartphone, numerous small plastic components serve vital, often unheralded, roles. Commonly, the NFC antenna is located on the rear housing, adhered to the back of the battery, or integrated into a larger flex cable near the camera module, loudspeaker, or wireless charging coil, typically in the upper or lower part of the phone's back. This comprehensive guide will equip you with the steps to systematically identify and fix a smartphone that randomly restarts. Power Off Device: Crucially, power off your smartphone before any inspection or cleaning attempts. An LCD display, much like its OLED counterpart, is susceptible to damage from drops, impacts, or pressure, resulting in cracks, dead pixels, discolored areas, or a complete loss of image. This guide will take you through the process of diagnosing and replacing a damaged digitizer, enabling you to restore full touch functionality to your smartphone. Intermittent Power: The phone powers on erratically or refuses to stay on. Smudges, fingerprints, or debris on the external lens glass are a common cause of blurry or hazy photos.

@Silvia, Not sure what you're trying to say but ok :)