[SOLVED] I'm looking for LG LMX520HM K Series repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my LG LMX520HM K Series. 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.

@Evelyn

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 LMX520HM K Series 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/684642/2012+titanium+2.0+diesel+kuga+the+key+fob+stopped+locking+the+car
Take a look at comment #1352
Also, this : https://www.ifixit.com/Answers/View/583527/Camera+and+Flash+Don%E2%80%99t+Work.
You can also check this video starting from minute 7:

The LG LMX520HM K Series 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 LMX520HM K Series 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 LMX520HM K Series 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 LMX520HM K Series 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/help-me-to-enable-it.1387201/

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

Workaround: Chip Transfer (Advanced Micro-Soldering): This is the only method for independent repair to potentially restore fingerprint functionality with a replacement physical button. If the problem persists after a factory reset, it's a strong indicator of a hardware fault. However, a properly replaced coaxial antenna cable will often restore full wireless functionality to the smartphone. In summary, addressing a persistent "over temperature" warning requires a methodical approach, starting with software diagnostics and progressing to a thorough hardware inspection. Separation: Prevent parts from rattling against each other, which can cause scratches or dislodge tiny components. Gently clean any old adhesive residue from the flex cable using IPA and a soft brush. Restart Device: A simple reboot can resolve temporary software glitches. As storage fills up, the operating system has less contiguous space to write new files, leading to fragmentation and slower access times. Secondly, power off your phone completely to prevent any short circuits or damage to sensitive internal components. Recovery Mode: Access custom recovery (like TWRP, if installed) or stock recovery. Reconnect Battery: Reconnect the battery FPC connector to the motherboard. Heating and gently nudging a suspect BGA chip can sometimes reveal loose solder joints. Aftermarket: Loose connection, intermittent charging, slow data transfer, or the charging cable may not click in properly. Multimeter Diode Mode: Use schematics to identify the power and data lines for the display on the logic board connector. Only use this if "Update" fails and you have no other options, or if you have an iCloud/iTunes backup. Any tactile unevenness, however subtle, is a primary indicator of misalignment. Navigate: Use the Volume buttons to navigate and the Power button to select. Physical Damage: Cracks, chips, or missing from the board entirely (often due to drops or aggressive prying). Charging Port Inspection: Check for debris, bent pins, or corrosion in the charging port. In rare cases, a manufacturing defect in the NFC chip or antenna could be the underlying problem. Replacement: For severely damaged cables (kinks, cuts, heavy corrosion) or broken connectors/receptacles, the only reliable solution is replacement. Always disconnect the battery before working on any part of the motherboard to prevent short circuits. Unresponsive Areas of Touchscreen: Certain parts of the screen might become unresponsive. Pressure-Sensitive Adhesive (PSA) Gaskets: These are the most common, used for display and back cover sealing. If the power management IC (PMIC) or specific power rails to the camera module are faulty, it can lead to intermittent operation or complete failure. Once the solder melts, use fine-point tweezers to lift the old array away. Data Transfer: Option to restore data from a previous device or cloud backup. If applicable, secure the display with any external screws (like Pentalobe screws at the bottom of iPhones). This can be more precise for some shields, but hot air is often necessary for the initial seating. Solution: Always keep the heat gun moving in slow, consistent circular or sweeping motions.

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