[SOLVED] I'm looking for Xiaomi Redmi 9C repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Xiaomi Redmi 9C. 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 Xiaomi Redmi 9C 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/886398/Truck+vibrated+between+45+mph+to+70+mph+when+gradually+accelerating.
Take a look at comment #445
Also, this : https://www.ifixit.com/Answers/View/396104/MacBook+Pro+Mid+2012.
You can also check this video starting from minute 9:

The Xiaomi Redmi 9C 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 Xiaomi Redmi 9C 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 Xiaomi Redmi 9C 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 Xiaomi Redmi 9C 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/418622/iPhone+5s+stuck+in+DFU+Mode

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

This is where advanced micro-soldering skills and diagnostic tools come into play. Fire and Explosion Hazard: If the swollen battery is punctured, overheated, or further compromised, the gases can ignite, leading to a thermal runaway event, fire, or even an explosion. True low-level reprogramming is largely outside the scope of independent repair due to OEM restrictions and proprietary tools. If you are using a larger sheet of acoustic foam, you will need to cut a tiny piece to precisely match the size and shape of the original filter. Android (Google Assistant): Open Google Assistant, tap your profile picture > Settings > Assistant > Voice Match. This often involves removing small screws, prying delicate connectors, and transferring components like microphones or haptic motors if they are integrated into the flex cable. If it recognizes it as a generic USB device but cannot access storage, it might be in a state where the bootloader is functional but the OS isn't. Missing Parts: Sometimes a broken clip piece might still be stuck in the frame. Always research your specific phone model's teardown guide (sites like iFixit are excellent resources) to understand the exact opening procedure. Research Your Specific Model: Search for a detailed teardown guide or video for your exact phone model (e.g., "iFixit iPhone 11 Power Button Replacement" or "Samsung Galaxy S20 Power Flex Replacement YouTube"). Failing RAM or Storage Chip: If the phone's memory or internal storage chip is failing, it can lead to constant system instability. A professional can accurately diagnose whether it's a loose connector, a faulty antenna, or a complete Wi-Fi IC failure, and advise on the most cost-effective solution.3. Extreme Cleanliness: Any dust, lint, or fingerprint trapped between the new polarizer and the display panel will be magnified and highly visible. Activate Flux: Allows the flux to become active, cleaning oxidation from pads and solder balls. Tack One Corner: Using your fine-tip soldering iron or hot air (briefly), tack one corner pad to secure the microphone in place. Adhesive Softening (Display/Back Panel/Battery): Start with a low to medium temperature setting, typically in the range of 60-80°C (140-175°F). Clean External Sensor Area: Thoroughly clean the top part of the phone's screen, especially around the earpiece. This security measure means that simply swapping a faulty sensor with a new, generic one will often result in a "fingerprint sensor not recognized" error or a complete loss of functionality. This effectively reinstalls the entire operating system, overwriting any corruption. It's a specialized chip that controls the boost converter, regulating the voltage and current supplied to the LEDs. Once the haptic motor is accessible, perform a thorough visual inspection: Disposal: Place the swollen battery in a fire-retardant bag or a bucket of sand. By Component Type: Separated bins for screens, batteries, charging ports, cameras, etc. Restart Device: A simple reboot can often resolve temporary software glitches. Manufacturers frequently release updates that include bug fixes, performance improvements, and updated display drivers, which could address known flickering issues. Diagnosing a flickering flashlight involves a methodical process, moving from the simplest software checks to more intricate hardware inspections. Small Pliers/Vise Grips (Precision): For gripping exposed screw heads or shafts. Scenario 1: Damage to the Wireless Charging Coil Flex Cable or its Connector (Coil Side) Protocol Management: Implementing cellular communication standards (GSM, CDMA, LTE, 5G). Preventative Measures are Key: There is no magic trick to recover data from a secure folder if its underlying encryption context is lost.

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