[SOLVED] I'm looking for Qmobile B800 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Qmobile B800. 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.

@Vincent

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 Qmobile B800 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/rsa-key-problem.3389109/
Take a look at comment #914
Also, this : https://www.ifixit.com/Guide/Melitta+Caffeo+Solo+microswitches+in+the+gear+drive+replacement/131912.
You can also check this video starting from minute 7:

The Qmobile B800 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 Qmobile B800 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 Qmobile B800 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 Qmobile B800 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/621103/Why+can+I+only+charge+my+phone+using+a+power+bank

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

Do not pull the display completely off yet, as it's still connected by flex cables. For smartphone repair technicians, the ability to accurately identify and interpret thermal discoloration is a critical diagnostic skill, as it often points directly to the source of various device failures, from performance degradation to complete device non-functionality. Dampen a lint-free wipe or microfiber cloth with 90%+ isopropyl alcohol. Press Gently: Once aligned, gently press down on the module to ensure its adhesive makes good contact with the phone's surface. Replacing an audio amplifier IC is not a simple modular component swap; it's an advanced micro-soldering task that requires specialized tools, a steady hand, and significant expertise in board-level repair. If buttons are worn or scratched, they can often be lightly sanded and polished (if plastic) or polished (if metal). Test in Safe Mode: Boot your phone into Safe Mode (disables all third-party apps). Ensure the wireless charging coil is properly connected to the motherboard. Flex Cables: Verify that all FPC (flexible printed circuit) cables are firmly seated in their connectors. The power button circuit is faulty: The PMIC isn't receiving the power-on signal (refer to Topic 6). Several factors can contribute to screen lift, both during and after a repair: Search for "black screen test" or "AMOLED black test" (even though you're testing an LCD, it works perfectly). Slower Wi-Fi/Bluetooth Speeds: Data transfer rates over Wi-Fi are noticeably slower, or Bluetooth audio experiences frequent stuttering or dropouts. Apply heat evenly around the perimeter for a minute or two, being cautious not to overheat any single area. Software Interference: Ensure no "headphone mode" software glitches are present. Identifying smartphone charge controller anomalies is a complex diagnostic process that moves from basic user checks to advanced professional hardware analysis. If it's consistently poor (-100 dBm or worse), the modem might be working harder, increasing "Cell standby" drain. Apply new adhesive strips or a thin, even bead of B-7000 glue to the perimeter of the new back cover frame (or the mid-frame, depending on your phone's design). Cure the Adhesive: If using liquid adhesive, allow it sufficient time to cure (usually several hours, refer to product instructions) before heavily using the camera or exposing it to dust/moisture. Frequent Full Discharges (0%): Constantly draining the battery to 0% before recharging puts more stress on the battery. Verify the new antenna contact springs/module are correctly installed and making solid contact. Carefully peel back these cables using a plastic spudger, being mindful not to tear them. Server Issues: Occasionally, the manufacturer's update servers might be overloaded or temporarily down. The secondary microphone is typically a very small SMD (Surface Mount Device) component, often integrated onto a flex cable that might also house other components like the earpiece speaker, power button, or volume buttons. Replacing a smartphone fingerprint sensor is a common repair, though its complexity varies significantly depending on the device's design and the sensor's integration. Widgets and Live Wallpapers: Animated widgets and live wallpapers require resources to load and run immediately upon boot, potentially extending the boot time. Follow this with a can of compressed air to blow away any remaining dust particles. Remember that patience and meticulous attention to detail are your best allies in smartphone repair. Without a DDI, the raw data from the AP would be meaningless to the physical display, resulting in a blank or garbled screen. If a high current persists, the fuse will blow, opening the circuit completely.

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