[SOLVED] I'm looking for Blu S91 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Blu S91. 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.

@Kasia

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 Blu S91 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/Info/Repairs
Take a look at comment #332
Also, this : https://www.ifixit.com/Answers/View/358754/2001+Yukon+brakes+and+power+steering+went+stiff+at+the+same+time+...
You can also check this video starting from minute 6:

The Blu S91 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 Blu S91 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 Blu S91 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 Blu S91 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/377945/Brake+drum+removal+Yamaha+golf+cart

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

Uneven Heating: Only one side of the component melts, leading to lifted pads when trying to remove. Use your phone normally until it completely shuts down due to low battery. Adhesive Remover (Isopropyl Alcohol - IPA): To dissolve stubborn adhesive residue. If part of the display assembly, inspect the area around the flex cable connection for any signs of physical damage or corrosion. An empty or non-functional field test mode also points to baseband failure. A dedicated phase meter would provide a direct reading of the phase relationship between two audio outputs. Factory Reset (Last Resort for Software): Back up all data and perform a factory reset. Allan variance provides quantitative values for these noise parameters, which are crucial for advanced sensor fusion algorithms and performance specifications. It describes the rate at which the angle error increases due to high-frequency noise. If it feels loose or misaligned within the tray before insertion, this could contribute to detection issues even if the tray fits the phone's slot perfectly. For stubborn spots, apply a small amount of IPA directly to the residue, let it sit for a few seconds to soften, then gently scrub or scrape with a plastic razor blade or sharpened spudger. Fuses are often overlooked but vital protective components in smartphone circuitry. Run your finger along the edge; it should feel perfectly smooth and clean. A systematic troubleshooting approach is key to resolving the issue and preserving your digital memories. It will be marked by a tiny hole next to the outline of the tray itself. Reseat the Cables: Carefully disconnect and then firmly re-seat all display-related flex cables. Use your magnification tool and flashlight to meticulously examine each individual pin within the connector. Battery Health: While less likely to cause idle drain specifically, an aging or faulty battery can lose charge quickly regardless of usage. The camera app might become noticeably slow, taking longer to process and save photos or record videos, potentially leading to missed shots or choppy recordings. Check if this flex cable is damaged, creased, or not seated correctly. Disconnect the Battery: Once the screen assembly is partially lifted, you will likely see a metal shield or tape covering the battery connector on the logic board. Do not overheat the center of the phone, as the battery is located there. "Ghost" Presses or False Triggers: The device might register a Force Touch event even with a light tap, or trigger actions unexpectedly when pressure is applied to a different part of the screen. The symptoms of smartphone RAM corruption can often overlap with other software or hardware issues, making accurate diagnosis challenging. Tilting the phone allows reflections to highlight subtle imperfections in the display panel itself. Cannot See Any Wi-Fi Networks: Even in areas with known-good networks, the phone detects nothing. Beep/Very Low Resistance (near 0 ohms): Indicates a short to ground, which is often problematic (e.g., a shorted capacitor or IC). Heat Application (Hot Air Rework Station): Set your hot air rework station to an appropriate temperature (typically between 300-380°C, depending on the solder type and board thickness) and a low airflow setting. Angle the light source at different positions (oblique lighting) to make dust particles more visible against the sensor's surface. CPU not responding: The CPU might be dead or not receiving its first power/clock signals, preventing it from performing its initial handshake with the PMIC.

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