[SOLVED] I'm looking for Unknown Pixi 3 8 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Unknown Pixi 3 8. 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.

@Ewelina

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 Unknown Pixi 3 8 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/435016/How+do+I+solve+software+crash
Take a look at comment #490
Also, this : https://www.ifixit.com/Guide/Asus+X502C-RB01+Keyboard+Panel+Removal/77656.
You can also check this video starting from minute 10:

The Unknown Pixi 3 8 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 Unknown Pixi 3 8 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 Unknown Pixi 3 8 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 Unknown Pixi 3 8 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/translation-app-hprojecttracker.3012650/

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

Clean and Organized: A cluttered workspace increases the chances of losing tiny screws or knocking over components. This helps to determine if the issue is with your specific pad or the phone. Thermal Cycling: Repeated heating and cooling can cause materials to expand and contract, eventually weakening solder joints. Batteries can explode, screens can be damaged, and other components might not withstand the cleaning solution or the cavitation. Connectors: These are the interfaces where flex cables attach to the logic board or other components. Charging: Especially during fast charging or wireless charging, the power delivery circuitry works intensively to convert and supply power to the battery. Dust and Grime: The most frequent cause of proximity sensor malfunction is obstruction. "Fingerprint Hardware Not Available" / "Sensor Not Calibrated" Error: A software message indicating a deeper hardware or driver issue. Mechanical Action - Fiberglass Brush/Pencil Eraser (Use with Extreme Caution): For persistent oxidation on flat, larger contact pads (e.g., battery terminals or antenna contact pads), a fiberglass brush pen or a pencil eraser can be used. Carefully lower the new screen into place, ensuring perfect alignment. Identify Target: Using schematics and board views, accurately locate the specific chip or memory area that contains the data to be read or written (e.g., the display EEPROM, the battery chip, the baseband EPROM). These carry signals and power and can act as antennas if damaged or improperly shielded. Access to these is often challenging for consumer devices but is invaluable when available. Loudspeaker: Typically found at the bottom of the phone, often integrated into a module that might also contain the charging port or vibration motor. Physical Repair Tickets/Forms: If digital systems aren't used, ensure paper forms are detailed, legible, and stored securely. Damaged Battery Flex Cable: If the damage is on the battery's flex cable and not the logic board connector, the entire battery (as the flex is usually integrated) needs to be replaced. Use your phone normally for a period, observing for any recurrence of ghost touch. Power it on and perform a final test of the proximity sensor and all other functions to ensure everything is working correctly. High-Demand Usage: Prolonged gaming, video streaming, or heavy multitasking, especially in a hot environment, can push the hardware limits. This often involves applying Kapton tape to protect nearby sensitive components from the heat of the hot air station. App-Specific Issues: Rarely, a poorly coded or malfunctioning third-party application might interfere with the display's refresh rate or graphics rendering, causing flickering when that app is in use. Corrosion: Check the motherboard connector for any signs of water damage. If the frame is bent or cracked, it can deform or damage the integrated antenna, impairing its performance. Identify Target Areas: Based on symptoms and visual inspection, identify components or areas likely to be causing or suffering from EMI. The NFC system in a smartphone typically consists of two main parts: the NFC chip, which processes the data (often integrated into the PMIC or a separate dedicated IC on the logic board), and the NFC antenna. Faulty Replacement Part: Though unlikely for a new part, the replacement daughterboard itself could be faulty. Angle-Dependent Polarizers: Some high-end displays might employ polarizers designed to optimize viewing angles. This might involve unscrewing brackets, disconnecting other flex cables (e.g., camera, display), or lifting a sub-board. Guide to Replacing the Dedicated Gaming Button Flex Cable on a Smartphone Do you hear any rattling? This could indicate a loose haptic motor or another component.

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