[SOLVED] I'm looking for LG G3100 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my LG G3100. 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.

@Matias

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 LG G3100 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/fm-radio.622741/
Take a look at comment #1706
Also, this : https://xdaforums.com/t/samsung-galaxy-s-ii-avilable-in-czech-republic.997345/.
You can also check this video starting from minute 7:

The LG G3100 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 LG G3100 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 LG G3100 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 LG G3100 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/667695/upgrade+possible+for+my+MacBook+Pro

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

This could lead to data theft, device manipulation, or your phone being used as part of a botnet. Look for burn marks, cracks, discoloration, or signs of liquid damage around these chips. Filter/Fuse: Often a very low-ohm resistor or fuse in the backlight circuit for protection against overcurrent. Allow the board to cool down naturally on the preheater before removing it. Power off the phone and disconnect the battery and screen again after testing. Known Good Display Assembly: A shorted display can sometimes prevent boot-up. Hardware USB Power Meter (Inline Device): This is the most accurate and reliable method for diagnosing charging issues. Thin, Non-Metallic Tool: A wooden toothpick, a plastic spudger, or a plastic flossing pick. Any deviation from original factory specifications during assembly or reassembly can compromise the device's integrity, negating its water-resistant properties entirely. Symptoms: "Cannot turn on Wi-Fi/Bluetooth" (toggle grayed out or fails), "Wi-Fi Scanning" or "Bluetooth Scanning" indefinitely. Lift it slightly, like opening a book, to check for these connections. Mastering these techniques empowers technicians to accurately pinpoint microscopic defects, perform intricate component-level repairs, and significantly improve repair success rates, ultimately extending the life of complex mobile devices. If a factory reset doesn't resolve the issue, it points towards a deeper hardware problem or a deeply ingrained firmware bug. Inspect and Repeat: After a few minutes of buffing, wipe away the polish residue with a clean microfiber cloth. This information is then sent to the phone's operating system, which adjusts the screen's backlight level accordingly. Start Simple: Begin by practicing on simple components on junk boards before moving to complex ICs or live devices. Power it on, go through initial setup, and verify no FRP lock before completing the purchase. The diagnostic process should always begin with the simplest checks to rule out common, easily resolvable issues. When callers complain that your voice sounds muffled, distorted, crackling, or too quiet, it's a clear indication that your main microphone is failing. Cold Joints: Are there any dull, lumpy, or grainy looking joints (insufficient heat)? Look for signs of liquid damage, burnt components, or missing surface-mounted components. Visual Inspection (Microscope): Inspect every single pin connection under the microscope. Improper Repair Attempts: If a device has been opened for repair, using incorrect type/quantity of adhesive, failing to properly clean old adhesive residues, or not allowing new adhesive sufficient curing time can lead to premature adhesive failure. Screen Rotation Not Working: Screen doesn't rotate automatically when the phone is tilted (ensure auto-rotate is enabled in settings). If the motherboard is not seated correctly, these contacts might not make proper connection, leading to weak or absent signal reception. Slow Charging: Despite a fast charger and compatible cable, the device charges unusually slowly. Low storage space can severely impact system performance and stability. Performance & Longevity: Genuine batteries are designed to meet specific performance standards, offering rated capacity and cycle life. Loose Flex Cable: The digitizer connects to the motherboard via a flex cable. If the issue persists, ensure your phone's operating system is updated to the latest version, as manufacturers frequently release updates that include Wi-Fi driver improvements and bug fixes.

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