[SOLVED] I'm looking for Xolo Q900s repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Xolo Q900s. 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.

@Samet

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 Xolo Q900s 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/648526/Can+someone+identify+this+part
Take a look at comment #1167
Also, this : https://xdaforums.com/t/skip-buying-a-case-and-replace-battery-cover.976502/.
You can also check this video starting from minute 5:

The Xolo Q900s 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 Xolo Q900s 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 Xolo Q900s 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 Xolo Q900s 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/swype-my-thoughts.704404/

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

Apply Stencil: Place the appropriate reballing stencil over the IC, aligning it perfectly with the pads. These are typically snap-on connectors, so gentle upward pressure from the bottom of the connector is usually sufficient. Conductive Copper/Aluminum Tape: This is a versatile and common DIY shielding material. Debris: Small foreign objects that have entered the device, such as tiny pieces of glass from a cracked screen, metal fragments, dirt, or hardened liquid residue. System Instability: The entire phone can become unstable, leading to crashes, freezes, or reboots. The exact button combination to enter recovery mode varies slightly between smartphone manufacturers and models. Low-light performance is often severely impacted, with increased noise and an overall muddy appearance. Adhesive: Many components, especially screens and batteries, are secured with extremely strong, proprietary adhesives. Inspect these for dust or obstructions and clean them gently with compressed air and a soft wipe. If it came with any pre-installed adhesive, ensure it's in good condition. Controlled Tilt/Movement: Slowly tilt your phone around each axis (roll it left/right, pitch it forward/backward). Go to your phone's Bluetooth settings and disconnect or "forget" any paired devices, then retest. Magnetometer (Compass): Detects magnetic fields, used for compass functionality and location services. When a temperature sensor fails or provides inaccurate readings, the smartphone's operating system may trigger various protective measures, such as: Old adhesive, if left behind, will create uneven surfaces and prevent the new adhesive from forming a strong bond, leading to the screen lifting again. If you do, clean it with IPA and a microfiber cloth specifically designed for optics. Remove the screen assembly and set it aside safely on a soft, clean surface. They are the arteries and nerves of your smartphone, carrying power, data, and sensor information. Corrosion: More severe chemical degradation, often caused by liquid ingress (water, sugary drinks, sweat) creating acidic or alkaline residues. Carefully inspect and re-seat all flexible connectors, particularly the battery FPC, display FPC, and charging port FPC. Use your precision screwdrivers to remove all screws, keeping them organized by type and location using your small container or a magnetic mat. Diffuser Films: Multiple layers of optical film that further homogenize the light and improve viewing angles. Weak Cellular Signal: When the phone struggles to maintain a strong connection to the cellular tower, its modem has to work much harder, transmitting at higher power to compensate for the poor signal. The most common causes include physical damage from drops or impacts, which can bend or break the springs. When you open a mapping app, the phone might take an unusually long time to pinpoint your location, or it might display "Searching for GPS" indefinitely. With the right equipment in hand, you'll be well-prepared to tackle a wide array of smartphone repair challenges.## 5. A smartphone motherboard is not a single flat piece of circuit board but a complex, multi-layered sandwich. Fitness Trackers Inaccurate: Step counts or activity tracking is unreliable. This conversion is crucial because the pixels themselves are essentially tiny light-emitting diodes or liquid crystal gates that respond to specific electrical stimuli. Filters/Duplexers: Small RF filters can be damaged by liquid or impact.

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