[SOLVED] I'm looking for Samsung SM-S721N Galaxy S24 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Samsung SM-S721N Galaxy S24. 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.

@Sara

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 Samsung SM-S721N Galaxy S24 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/Guide/Dell+Latitude+E5400+Hard+Drive+Replacement/141867
Take a look at comment #984
Also, this : https://xdaforums.com/t/sound-problem.322456/.
You can also check this video starting from minute 1:

The Samsung SM-S721N Galaxy S24 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 Samsung SM-S721N Galaxy S24 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 Samsung SM-S721N Galaxy S24 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 Samsung SM-S721N Galaxy S24 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/a800i-usbsettings-has-stopped.3531148/

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

Signal Interference: Wi-Fi, Bluetooth, cellular, and GPS signals can become weak, intermittent, or completely drop out. Connect the logic board to a screen and battery (outside the phone frame if possible). Black Probe on Pads: Using the schematic and boardview, identify key test points or pads around the Tristar/Hydra chip. Observe the chip: As the solder balls melt and reflow, the chip will subtly "settle" or "snap" into perfect alignment due to the surface tension of the molten solder. Intermittent Functionality: Features like Wi-Fi, Bluetooth, cellular signal, camera, or touch screen might work sometimes and fail at other times. Factory Reset Glitch: Rarely, a factory reset might fail and corrupt system files. Effectiveness: Can work for stubborn screws but carries very high risk. Open the Device & Disconnect Battery: Follow a reputable repair guide specific to your phone model. Faulty New Cable: Rarely, the replacement cable itself could be defective. Repeated Connection/Disconnection: While designed for a certain number of cycles, excessive or rough handling can wear out the pins. Infrared Camera: This specialized camera captures the IR light reflected from the face, including the distorted dot pattern projected by the dot projector. If the camera struggles to focus but otherwise produces a clear (albeit unfocused) image, the autofocus motor might be malfunctioning. USB Cable: A genuine Apple Lightning-to-USB cable or a certified MFi (Made for iPhone/iPad) cable. Physical damage or liquid damage can also lead to intermittent connections or component failures that manifest as forced restarts. If multiple people across different devices and networks report the echo, the problem is almost certainly with your phone. In Fastboot Mode, in your command prompt/terminal, type: `fastboot flashing unlock` Function: Repels oils and grease, reduces friction for smoother finger glides, and makes the screen easier to clean. It contains multiple small pins (e.g., 4-24 pins for USB-C, 8 pins for Lightning, 5 pins for micro-USB) that must make solid contact with the corresponding pins on the cable. Fluctuating or extremely low/high current can indicate a problem with the charge controller or the power negotiation process. This requires a steady hand and a light touch; excessive force will likely break the pin or its internal spring. Disconnect Battery: Locate the battery connector on the logic board and carefully pry it up with a plastic spudger. Android: Power off the device (if possible, or let it loop until the battery dies). When the PS malfunctions, the screen may remain on during calls, leading to frustrating accidental inputs, or it might incorrectly black out the screen even when not near the face. By following these steps, you can significantly improve your chances of restoring your smartphone's Wi-Fi to full strength.3. Reconnect the Battery: Carefully snap the new battery's flex cable back into its connector on the logic board. Fastboot Mode (various Android): Similar button combinations (e.g., Volume Down + Power). Bent Frame: A bent or twisted device frame can put uneven pressure on the display assembly, distorting the pressure sensors. A perfectly clean and dry surface is paramount for the new adhesive to bond correctly. Power it back on, and as the manufacturer's logo appears, press and hold the Volume Down button until the phone fully boots. Repair: Component replacement, trace repair, or micro-soldering remediation of liquid damage.

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