[SOLVED] I'm looking for G-BEST 8820 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my G-BEST 8820. 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.

@Melinda

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 8820 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://www.ifixit.com/Answers/View/774446/I+have+this+iPhone+but+it's+icloud+account+is+locked+.
Take a look at comment #1570
Also, this : https://xdaforums.com/t/opinions-needed-on-phone-upgrade.564182/.
You can also check this video starting from minute 2:

The G-BEST 8820 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 8820 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 8820 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 8820 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://www.ifixit.com/Answers/View/278906/Why+is+my+screen+flickering+and+the+programs+aren't+loading.

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

Corrosion: Severe liquid damage can corrode the frame, especially metal-infused plastic ones. Network Mode Selection: For each SIM, check the preferred network type (e.g., 2G/3G/4G/5G automatic, or manual selection). Hot Air Rework Station: Absolutely critical for desoldering and soldering surface-mount components like the SIM reader. In the intricate world of smartphone repair, damage to the Printed Circuit Board (PCB) is one of the most challenging problems. If misaligned, the proximity sensor might always detect an object (screen stays off) or never detect one (screen stays on during calls, leading to accidental touches). IMPORTANT: Disconnect the battery first as soon as you open the phone. Schematics will provide the component's part number and location on the PCB, often labeled as "MAG," "COMPASS," or by its manufacturer's specific IC code (e.g., AKM, Bosch, STMicroelectronics). With the device partially reassembled (battery connected, screen connected but not sealed), power it on. As lithium-ion batteries age or are exposed to excessive heat, they can expand, exerting pressure against the internal components and, subsequently, the screen or back panel. Physical Impacts: Drops, bumps, or bending can deform the frame, crack glass, or loosen adhesive seals, even if superficially the phone looks fine. Slide Around the Edges: Carefully slide a pick along the edges of the phone, slowly separating the adhesive. Be mindful of flex cables connecting the display, which are often located on one side or the bottom. Capillary Action: Liquid can wick into nearly every crevice, under ICs, and into connectors, making thorough cleaning challenging. MIPI (Mobile Industry Processor Interface): A suite of standards widely used for high-speed communication between the SoC and peripherals like cameras (CSI) and displays (DSI). Pentalobe/Philips screwdrivers, spudgers: If phone disassembly is required. Other FPC Cables: Check all major flex cables (display, charging port, camera) for proper seating and any signs of damage. Also, check for shorts to ground on either side of the coil; a short on the output side could indicate a shorted backlight IC or shorted LEDs. Excessively high temperatures during charging or even idle usage can be a sign of a failing charge controller or other power component. Initial Test (before final sealing): If possible, power on the phone before fully sealing it. Preferred Network Type: Go to Settings > Network & internet > Mobile network > Preferred network type (or similar). Ensure it clicks properly and performs its intended functions (e.g., back to home, recent apps). Ensure Proper Seating: Make sure the cables lie flat within the guides, are not twisted or bent sharply, and are not under any tension. This can lead to sudden voltage drops, causing the phone's power management integrated circuit (PMIC) to trigger a protective shutdown and restart. Place the bare frame on a flat, protected surface (e.g., with a soft cloth underneath). Cracks or Gaps: Thoroughly examine the screen and back glass for any cracks, even hairline fractures. Entry-level thermal cameras, often smartphone attachments or handheld units, offer sufficient resolution for general board scanning. While relatively simple, this mechanism can suffer damage from physical force, material degradation, or improper use, leading to an inability to insert or remove SIM cards, which effectively disables your phone's primary function as a communication device. Wi-Fi audio solutions, like screen casting, can also add their own set of latencies due to network conditions and encoding/decoding overheads. Reassemble Components: Replace any components you removed in reverse order. While on the "no command" screen, press and hold the Power button for about 10-15 seconds until the phone restarts.

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