[SOLVED] I'm looking for LG LMK500QN K Series repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my LG LMK500QN 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.

@Barb

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 LMK500QN 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://xdaforums.com/t/can-i-flash-the-original-x2-rom-into-the-x1.628463/
Take a look at comment #175
Also, this : https://www.ifixit.com/Answers/View/530101/Phantom+home+button+nani.
You can also check this video starting from minute 5:

The LG LMK500QN 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 LMK500QN 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 LMK500QN 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 LMK500QN 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://www.ifixit.com/Answers/View/332469/Display+is+completely+black

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

Navigate: Use the Volume buttons to navigate and the Power button to select. Surrounding Components: Inspect passive components (resistors, capacitors, inductors) around the audio IC for damage or missing parts. The central pin can bend or break, and the outer metal housing can deform. Using the wrong screw in the wrong hole can cause damage (e.g., puncturing the motherboard). You'll need a Windows PC, correct USB drivers for your phone (ADB and Fastboot drivers are a good starting point), and the appropriate flashing tools. Factory Reset: If all software troubleshooting fails, a factory reset (after backing up all data) can rule out deep software conflicts or corruption. Software Interference: Ensure no "headphone mode" software glitches are present. Closer to 0 dBm is better (e.g., -80 dBm is good, -120 dBm is very poor). Gathering the correct tools is paramount for a successful and safe repair: It often contains multiple `.img` files (boot, system, vendor, radio, etc.) and a `flash-all.bat` (Windows) or `flash-all.sh` (Linux/macOS) script. Port Gaskets: Some phones have tiny gaskets around the charging port or headphone jack. Digitizer Controller IC Failure: The integrated circuit (IC) on the logic board or the display assembly that interprets touch input can fail, leading to partial or complete unresponsiveness. Continuity: Use a multimeter in continuity mode to check for breaks in these traces between the SIM card reader and the baseband processor (or intermediary components). Read Instructions Carefully: Follow unlocking and flashing guides meticulously, specifically for your device model. Filter Coils, Diodes, Capacitors: Associated passive components in the backlight circuit. Video Guides: Always search for a specific video guide for your phone model. - Greenish-blue or White Powdery Residue: This is the most common and definitive sign of copper oxidation (patina or verdigris). Slow Wireless Charging: Significantly slower charging times compared to normal. Apply Flux: Apply a thin layer of liquid flux to the pads on the logic board where the connector will sit. On the other hand, it introduces significant risks related to security, stability, warranty, and app compatibility. Damage to even a single critical via can disrupt entire circuits, leading to component failure, signal loss, shorts, or complete device malfunction. This should only be attempted by experienced technicians with the right equipment (hot air, preheater, microscope, reballing stencil). Then, without fully reassembling, test the display to see if the issue is resolved. Counterfeit batteries might attempt to mimic OEM labels but with subtle errors. If the haze is due to external dirt, smudges, or fingerprints, a simple yet effective cleaning process can resolve the issue. Apply very minimal, indirect heat to the edges of the back cover or screen (depending on your phone's access point) to soften adhesive. It's usually located beneath the back cover, sometimes adhered directly to it or to the mid-frame, positioned to align with the charging pad. Secure the Board: Place the logic board securely on an ESD-safe holder or mat. Always double-check connections and test thoroughly before fully sealing the device.### 3. Via Recovery Mode: If you can't boot into Android, access Recovery Mode (as described in 2.E).

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