[SOLVED] I'm looking for LG LMK520BMW K Series repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my LG LMK520BMW 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.

@Jay

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 LMK520BMW 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/is-it-possible-to-install-a-lg-h850-europian-rom-on-lg-h860.4149445/
Take a look at comment #1390
Also, this : https://www.ifixit.com/Answers/View/906304/Solid+white+light+after+plugging+in.
You can also check this video starting from minute 9:

The LG LMK520BMW 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 LMK520BMW 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 LMK520BMW 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 LMK520BMW 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/559960/Ps+4+pro+overheating

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

Minor corrosion can often be removed by gently scrubbing with IPA and a soft brush or a fiberglass pen (very carefully). Android: Settings > System > Reset options > Erase all data (factory reset). General Visual Inspection: Once the phone is open, locate the various antenna cables. Feathering (Advanced): For best results, lightly sand the edges of the dried paint with extremely fine sandpaper (6000-8000 grit) to blend it. They come in various thicknesses, hardnesses, and thermal conductivities. Authorized service centers and manufacturers have proprietary tools and software that can legitimately program a new logic board with an IMEI. Procedure: Power off the phone, remove the SIM tray, open the device (back cover or screen removal depending on model), disconnect the battery. After exhaustive troubleshooting: If you've tried everything (software, carrier, and basic hardware checks) and still have no signal. It can bridge electrical contacts, leading to short circuits and component failure. Physical Damage: If the phone was recently dropped, suffered water damage, or was bent, the storage chip (which is a BGA component soldered to the PCB) could have been physically damaged, its solder balls cracked, or its connections corrupted. Sometimes, the trace leading to the missing pad can be extended, or an adjacent via (a plated through-hole connecting layers of the PCB) can be utilized if the schematic confirms its connectivity. These screws typically hold down metal shields, flex cable connectors, specific internal components (like speakers, camera modules), or even the battery. The USB-C port has become the universal standard for modern smartphones, offering reversible connectivity, faster charging speeds, and higher data transfer rates compared to its predecessors like micro-USB. Microphone Interference: Noise picked up by the microphone during calls while charging, making the user's voice unclear to the other party. Remove the Screen: Once all cables are disconnected, carefully remove the screen assembly and set it aside in a safe, dust-free place. A soft-bristled, dry toothbrush, a small artist's brush, or a can of compressed air (used cautiously from a distance to avoid pushing debris deeper or damaging the delicate internal membrane) can be effective. Most ICs have an orientation mark (a dot, a line, or a chamfered corner) that must match the corresponding mark on the PCB. Physical Impact: A drop or blunt force trauma can crack the plastic housing of the connector, break its internal pins, or even detach the entire connector from its solder pads on the motherboard. Using fine scissors or an exacto knife, precisely cut the new material to match the shape and size of the original. If all else fails, and you're confident in your repair skills, the issue might lie deeper within the motherboard, perhaps with the trace lines leading to the sensor, which would require advanced micro-soldering skills or professional repair. Connectivity Problems: Wi-Fi, Bluetooth, or cellular data not turning on, constantly dropping connection, or failing entirely. The gyroscope/magnetometer (IMU) chip is typically a very small, multi-pin IC, often a BGA (Ball Grid Array) or LGA (Land Grid Array) package, located near the main CPU or on a separate flex cable near the top of the phone (sometimes integrated with the proximity/light sensor flex). ADB (Android Debug Bridge) & Fastboot: Command-line tools that facilitate communication between a computer and an Android device, essential for flashing and debugging. Motherboard Connector Continuity: For very advanced cases, check continuity from the motherboard connector pins to their respective test points or ICs on the motherboard. Use the multimeter to perform a continuity check from the charging port pin (now connected via the jumper) to the original destination component. Gentle Handling During Repairs: Always use plastic tools when prying connectors and be extremely careful not to apply excessive force to clips. This removes any remaining adhesive bits, oils, dirt, and fingerprints. With the right tools, a good quality part, and careful attention to detail, you can successfully restore full touch functionality to your smartphone.### 2. Battery Issues: A severely degraded, damaged, or completely dead battery might not be able to accept a charge. If it were to accidentally spill or squish onto surrounding components, a conductive paste could cause a short circuit.

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