[SOLVED] I'm looking for LG LMK300CM Risio 4 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my LG LMK300CM Risio 4. 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.

@Liz

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 LMK300CM Risio 4 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/why-is-data-icon-always-on-statusbar.1693321/
Take a look at comment #789
Also, this : https://xdaforums.com/t/q-i9100-on-aws-1700-2100.2077470/.
You can also check this video starting from minute 10:

The LG LMK300CM Risio 4 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 LMK300CM Risio 4 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 LMK300CM Risio 4 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 LMK300CM Risio 4 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/252442/Possible+uses+for+retired+iPhone+3G+8GB

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

New Adhesive Strips (Optional but Recommended): For re-sealing the display or back cover. Slide in Flex Cable: Carefully and straightly slide the flex cable fully into the connector's slot. Verify that the physical volume buttons on the outside of the phone have proper tactile feedback and move freely. Disconnect it, clean the connector pads on both the flex and the motherboard with IPA and a lint-free swab, and then reconnect it firmly and squarely. Arrows, circles, and text overlays can draw attention to specific damage points, making the documentation clearer for both clients and fellow technicians. The LED array itself is a small strip or cluster of tiny light-emitting diodes, often mounted on a flexible circuit board or directly on the display panel's flex cable. While a simple dead battery or screen might be the culprit, a persistent no-power issue often points to deeper problems within the logic board's power delivery system or critical ICs. Position the Cable: Carefully place the new power flex cable into the exact position where the old one was. Motherboard Removal: Remove all screws securing the motherboard to the phone's frame. Approach: Connect your phone to a PC and run `adb logcat > log.txt` (or use a persistent logging app). By following these detailed steps, maintaining extreme organization, prioritizing correct screw placement, and exercising patience, you can ensure a successful repair, preventing critical damage and restoring your device's full operational integrity.Multi-pin connectors are ubiquitous within smartphones, serving as vital interfaces for everything from charging ports and display connections to camera modules, SIM card readers, and various flex cables. Any bright colored dots (red, green, blue, or even white) against this black background are prime candidates for stuck pixels. Warranty and Returns: A reputable supplier will offer a clear warranty and return policy for defective parts. Profile Development: Mastering thermal profiles is challenging and often requires extensive experimentation. Under a microscope, if a broken trace is identified leading from the button connector to the PMIC, a fine-gauge enamel-coated jumper wire can be soldered to bridge the gap. However, excessive or prolonged overheating of the storage chip can lead to a cascade of problems, from performance degradation to data corruption and complete device failure. Short Circuits on PCB: A severe short circuit caused by liquid damage, physical impact, or component failure can draw excessive current, leading to localized heating and potential runaway. By meticulously following these steps, you can ensure a clean surface, leading to a much more durable and professional-looking repair, enhancing both the functionality and longevity of your smartphone. Patience and a Steady Hand: These are your most important non-tangible tools. Several popular professional tools facilitate EMMC/UFS data recovery and repair: Volume Buttons: Both Volume Up and Volume Down work, increasing/decreasing media volume. Initial Power On Test: Before completely sealing the phone, gently press the power button to see if it powers on. The repair process commences with the careful disassembly of your smartphone. Examine grayscale gradients: Pay close attention to the transition from black to white. These can often be identified by their irregular patterns or crystalline appearance after drying. Modern smartphone motherboards are incredibly dense, compact, and feature multiple internal layers where traces (electrical pathways) are routed. Caveat: This is only accurate if the resistor is not in parallel with other low-resistance components. OLED displays, prevalent in modern smartphones, are highly susceptible to "burn-in" or permanent discoloration when exposed to excessive or prolonged heat. Use a high-quality microfiber cloth and a screen cleaner (if necessary) to remove all smudges, fingerprints, and surface dust. Factory Reset Protection (FRP): For Android devices running 5.1 Lollipop or later, FRP is a security feature.

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