[SOLVED] I'm looking for Chea A90 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Chea A90. 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.

@Bridget

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 Chea A90 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/408076/How+can+I+reprogram+the+Blu+Studio+5.5+to+get+into+it
Take a look at comment #28
Also, this : https://www.ifixit.com/Guide/Mac+Pro+First+Generation+HDD+Replacement/13270.
You can also check this video starting from minute 6:

The Chea A90 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 Chea A90 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 Chea A90 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 Chea A90 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/sky-go.2394563/

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

Securing the Board: Place the motherboard securely in a universal PCB holder or jig. Good Lighting: A desk lamp or flashlight is crucial for clear visibility. OLED (Organic Light-Emitting Diode) displays have become the gold standard for high-end smartphones, celebrated for their vibrant colors, deep blacks, high contrast ratios, and energy efficiency. Regardless of how your phone opens, the very next crucial step after gaining internal access is to disconnect the battery. While designed to be resilient, they remain vulnerable to environmental factors like moisture, dust, and corrosion, especially after undergoing repairs that might compromise original factory seals or expose bare solder joints. Component Protection: Apply Kapton tape to shield any very close, sensitive components that might be affected by the heat from the hot air station. Plastic Spudgers and Prying Tools: For safe disassembly and handling of display flexes. Then, remove all screws securing the motherboard and carefully lift it out. Not all cables are created equal; some are only good for data, not high-speed charging. Alternatively, a tiny dab of suitable non-conductive epoxy can be used, but solder mask is often preferred for its precision and electrical properties. Identifying smartphone motherboard short circuits is a challenging but essential skill for advanced repairs. An integrated circuit (IC) chip directly on the main logic board (motherboard). Corrosion: Check for green, white, or blue residue on the speaker module's contacts or within its housing, indicating water damage. Avoid Constant 100% Charge: Don't leave your phone plugged in at 100% charge for extended periods (e.g., overnight, every night), especially if it doesn't have smart charging features that limit charge to 80% for longevity. Physical Damage: Under good light, inspect the area where the magnetometer is located. Fault Points: Communication can fail at the module IC itself, the SoC, the traces on the PCB, flex cables, or the connectors. Forcing screws can strip threads on the posts, damage the motherboard, or even crack the PCB. Connecting an iPhone to a computer running software like iMazing, CoconutBattery (for macOS), or 3uTools can sometimes provide more detailed battery health and temperature information. Impact Damage: A severe drop can dislodge components, crack solder joints, or damage integrated circuits (ICs) on the logic board. Liquid Damage: Even if external signs are minimal, internal liquid damage can cause shorts on the motherboard, particularly around the charging control components. PMIC (Power Management IC): No power, not charging, rapid battery drain (phantom drain), device randomly shuts off. The new adhesive will not bond properly to old, gummy residue, dust, or grease. To enter Safe Mode: Press and hold the power button until the power menu appears. Component Ground Pins: With schematics, identify the ground pins of key ICs (power management ICs, Wi-Fi ICs, audio ICs). Check for Software Updates: Outdated software can sometimes have bugs that affect charging. They must be perfectly flat, shiny, and free of old solder bumps or residue to ensure the new microphone seats correctly. In conclusion, the "decryption unsuccessful" error is a severe problem for smartphone users. Open Phone: Most phones open either from the display side (requiring heat to soften adhesive and careful prying) or from the back cover (similar process). Action: As a final software troubleshooting step, perform a factory reset on the host phone. Incorrect Timing: Even if signals are present, their timing relative to each other (e.g., data valid time after clock edge) might be incorrect.

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