[SOLVED] I'm looking for Htc S740 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Htc S740. 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.

@Priyanka

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 Htc S740 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/anyone-screw-up-on-the-mail-in-rebate.709378/
Take a look at comment #704
Also, this : https://www.ifixit.com/Answers/View/679801/Why+is+my+phone+glitching.
You can also check this video starting from minute 3:

The Htc S740 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 Htc S740 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 Htc S740 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 Htc S740 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/801648/How+to+remove+alternator

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

Reseating the flex cable, though less common for AF problems than for complete camera failure, can sometimes resolve intermittent power/data issues that might be affecting the AF motor. Thermal Camera: A thermal imaging camera can precisely identify hot spots on the logic board during charging. Any data you wish to restore must come from a cloud backup or an external backup you performed before the logic board replacement. Selecting the right magnification tools is a critical decision for any repair technician, impacting precision, efficiency, and ultimately, the quality of the repair. Configure it to log raw angular velocity data (rad/s or deg/s) for X, Y, and Z axes. Power Off: Always power down your phone completely and disconnect the battery before cleaning. Precision Screwdriver Set & Tweezers: For disassembling the smartphone. Check for continuity from these pins to their respective connection points on the motherboard connector. Gently pull up on the suction cup while inserting a thin opening pick (or a playing card) into the gap created between the display and the frame. As the IPA evaporates rapidly from the hotter component, or the freeze spray dissipates quickly, the thermal camera will show a more pronounced and rapidly changing thermal signature, often pinpointing the exact IC or capacitor responsible for the short. Reseating Connectors: If the connectors are merely loose, carefully snap them back into place, ensuring they are fully seated. If the heat disappears, the daughterboard (or a component on it like the charging port itself, microphone) is the issue. This method carries a higher risk of deforming the frame further if not done precisely. Downloads Folder: Check your `Downloads` folder for large, forgotten files (installer APKs, old documents, videos). When exposed to liquid, these indicators change color, typically to red or pink. If the debris is compacted, carefully use your non-metallic tool (wooden toothpick, plastic spudger) to gently scrape it out. Magnifying Lamp or Microscope: Absolutely essential for precise work on tiny components. Antenna System: Damaged coaxial cables, antenna flexes, or antenna connectors are common and simpler causes of "no service." POS (Point of Sale) Systems with Inventory Modules: Integrates sales, repairs, and inventory, offering a comprehensive solution. The SIM (Subscriber Identity Module) tray is a small but essential component of any smartphone, enabling the device to connect to a cellular network. Fine-tipped Probe/Tweezers: For gently manipulating pins, removing debris, and testing cable fit. Test the SIM Card in Another Phone: Conversely, if the problematic SIM card works in another phone, it confirms the SIM card is fine, and the issue is definitely with the phone. Use a Preheating Plate: A preheating plate (bottom heater) heats the entire PCB from below to a moderate temperature (e.g., 100-150°C). Download manufacturer's flashing tool: Examples include Odin for Samsung, MiFlash for Xiaomi, SP Flash Tool for MediaTek devices. Initial Setup: If successful, the phone should boot into the operating system or recovery mode, allowing you to proceed with a full system restore or setup. Finally, after exhausting these diagnostic steps, cross-referencing your findings with online forums, manufacturer support websites, and user communities can be invaluable. You can usually find them by searching "Qualcomm QDLoader 9008 driver" along with your device model. Power Management IC (PMIC): This is the ultimate recipient of the power button signal. Further Device Damage: Incorrect voltage or current from a faulty PMIC could fry other components. Phone Doesn't Charge At All: Even with a known good charger, cable, and battery, the phone shows no charging indication and battery percentage doesn't increase.

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