[SOLVED] I'm looking for DESAY DS-M903 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my DESAY DS-M903. 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.

@Lila

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 DESAY DS-M903 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/419624/Phone+won't+turn+on
Take a look at comment #672
Also, this : https://www.ifixit.com/Answers/View/373635/Can+I+use+a+charging+port+for+a+10+in+on+my+7.0+in+instead.
You can also check this video starting from minute 10:

The DESAY DS-M903 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 DESAY DS-M903 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 DESAY DS-M903 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 DESAY DS-M903 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/Guide/HP+Deskjet+F4480+Scanner+Light+Replacement/12756

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

Charge Your Device Fully: Backups, especially large ones, can consume significant battery life. Dust Ingress: Microscopic dust particles getting trapped between layers during re-lamination, creating visible bubbles. Restart Your Phone: A simple reboot can resolve software glitches that might be preventing charging. Ensure the surface is perfectly clean and dry for optimal adhesion of the new flex cable. Metal EMI Cages/Shields: These are small metal cans soldered directly onto the PCB (Printed Circuit Board) over sensitive components like the processor, Wi-Fi module, or RF transceiver. It leaves minimal, typically non-conductive, and non-corrosive residue. Consult a Teardown Guide: Before touching your phone, find a disassembly guide or video for your exact model (e.g., iFixit). Pay close attention to power ICs, charging ports, and battery connectors, as these are common points of failure. Dental picks, fiberglass scratch brushes, or very fine brass brushes can be used carefully under a microscope to physically scrape away stubborn corrosion. Reliable USB Cable: Use an original Apple Lightning cable or a high-quality MFi-certified cable. Factory Reset (Last Resort): If all else fails and you suspect a software issue, a factory reset (after backing up all data) can sometimes resolve deep-seated software conflicts. If you are not confident, it is always best to seek professional repair to avoid irreparable damage to your device.10. Suction Cup: To help lift the display assembly (if opening from the front). Front display removal: Use a suction cup and opening picks after heating the display edges. This unit provides comprehensive motion data to the phone's processor. Refer to a specific repair guide for your device (e.g., iFixit, YouTube tutorials). Scalpel/Razor Blade: For carefully removing underfill (if present) or adhesive. This detailed analysis is instrumental in performing effective and lasting repairs, restoring the device's functionality and preventing future thermal failures.5. Highly Advanced Micro-soldering: Some repairs, such as replacing CPUs, dedicated ISPs, or complex BGA reballing (beyond the basic fuse or connector), require highly specialized equipment and years of micro-soldering expertise. However, this miniaturization comes with increased fragility at the component level. Physical Damage: A drop or bending can crush battery cells, causing an internal short. Aftermarket: Gaps between glass and frame, misaligned cutouts, visible glue residue, or cheaper plastic frame materials. Apply heat evenly around the edges of the screen (typically 1-2 minutes with a heat gun, or follow iOpener instructions). Adhesive Application: A new, optically clear adhesive (OCA) layer is needed. If the new Audio Codec IC is a BGA package and not pre-balled, you will need to reball it (see Topic 3 for detailed reballing instructions: clean chip, use stencil, apply solder paste, reflow, clean). Authorized service centers and manufacturers have proprietary tools and software that can legitimately program a new logic board with an IMEI. Some pressure marks might only be visible at specific brightness settings, often becoming more prominent at lower brightness or on uniform backgrounds. Puncture: Puncturing a LiPo cell exposes its internal chemicals to oxygen, triggering a rapid chemical reaction that releases heat and gas. Apply the coating in even, sweeping passes, moving the can constantly to avoid concentrating the spray in one spot. Stand: A sturdy boom stand or articulated arm for flexibility and stability.

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