[SOLVED] I'm looking for BBK Vivo Y928 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my BBK Vivo Y928. 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.

@Katja

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 BBK Vivo Y928 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/kernel-21-09-gcc-4-10-sm-uber-sense6-4-4-3-hacker-kernel-for-htc-one-m8-intl.2870937/
Take a look at comment #1205
Also, this : https://www.ifixit.com/Answers/View/576192/iPad+Mini+dead+after+digitizer+replacement.
You can also check this video starting from minute 5:

The BBK Vivo Y928 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 BBK Vivo Y928 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 BBK Vivo Y928 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 BBK Vivo Y928 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/windowed-ui-on-70it.1615256/

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

Battery Issues: A severely discharged or failing battery can sometimes lead to erratic boot behavior, including getting stuck in Fastboot. When connected to a computer, pull down the notification shade on your phone and tap the USB notification. LDO (Low-Dropout Regulator) Outputs: The PMIC contains numerous LDOs that step down the VCC_MAIN voltage to lower, stable voltages required by specific components (e.g., 1.8V for certain ICs, 3.0V for display, 1.2V for CPU core). However, these devices, having survived years of use, often bear the scars of time: scratched screens, dented frames, worn buttons, and discolored plastic housings. A hard brick, on the other hand, means the device is completely unresponsive. This step is very risky and should only be attempted if you are confident in your dexterity and understand the risk of permanent damage. Any specific symptoms, when the problem started, and what steps the customer has already taken. Furthermore, small starch particles and dust from rice can get into ports and components, causing more problems. Workspace Protection: Cover your work surface with a mat or old towel that can be easily cleaned or disposed of. An incorrect programmer file or XMLs will result in QFIL errors or a failed flash. In Safe Mode, only pre-installed applications run, which can help determine if a third-party app is interfering with the sensor's operation. A via is essentially a small hole drilled through the PCB, the inner walls of which are plated with a conductive material, typically copper. Phase 2: Functional and Internal Indicator Checks (Advanced User/Technician Assessment) Could be bad solder joints, incorrect chip programming, heat damage to surrounding components, or an underlying motherboard issue not related to NAND. A faulty ALS can lead to a screen that is perpetually too dim or too bright, or one that flickers erratically. Isopropyl Alcohol (IPA): 90%+ pure IPA is used for thorough cleaning of the board before and after the repair, removing dirt, corrosion, and flux residue. It manages the radio frequency (RF) transceiver, power amplifiers, and various other components that process signals between the phone's antenna and the cellular network. Thermal Cycling: Repeated heating and cooling cycles (from device usage, charging, or environmental changes) cause the solder and PCB materials to expand and contract at different rates, leading to fatigue and cracking. Surface tension will help it snap into place during reflow, but initial alignment is critical. It requires immense patience, a steady hand, meticulous attention to detail, and considerable practice. The reballed (or new) BGA chip is carefully aligned onto the motherboard pads using a microscope. No Power / Dead Phone: If a main power line fuse blows, the entire phone may not power on. Install a reputable third-party camera app (e.g., Open Camera, GCam mod if applicable) that allows manual control over white balance. Misapplication of heat can lead to a range of issues, from cosmetic damage to severe component failure, including battery fires. Carefully peel back these cables using a plastic spudger, being mindful not to tear them. Work in a clean, well-lit, and organized environment to prevent misplacing tiny screws and to minimize dust contamination, especially when dealing with the display. It also places greater stress on the multi-layered PCB, potentially leading to warping, delamination, or damage to internal traces. Crucially, it must have adjustable temperature settings to avoid overheating sensitive components like batteries. The logic board will detect a mismatch between the serial numbers of the installed components and the ones it expects, and Face ID will be permanently disabled, displaying the "Face ID Not Available" message. Excessive current at any stage, especially after the initial boot logo, can pinpoint a problem.

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