[SOLVED] I'm looking for REXPOWER C18A repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my REXPOWER C18A. 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.

@Ralph

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 REXPOWER C18A 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/341496/How+do+I+remove+my+battery
Take a look at comment #1020
Also, this : https://www.ifixit.com/Answers/View/7209/How+to+troubleshoot+a+gray+screen+on+start+up..
You can also check this video starting from minute 3:

The REXPOWER C18A 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 REXPOWER C18A 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 REXPOWER C18A 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 REXPOWER C18A 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/503667/I+just+got+a+battery+replacement+yesterday

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

Books: Place the phone face down on a soft cloth, and place a few heavy books on top, ensuring even pressure. Re-evaluate Custom ROMs: If a custom ROM is causing issues, try a different, more stable version, or revert to stock firmware. By starting with simple software checks and gradually moving to physical inspections, you can narrow down the potential causes. Re-flashing the stock ROM (the original firmware provided by your phone's manufacturer) can overwrite all system partitions with a fresh copy, effectively 'unbricking' the software. This guide will walk you through the process with an emphasis on safety, proper handling, and disposal. Next, power off your phone completely to prevent any accidental short circuits or damage to sensitive internal components during the process. You'll need the Odin software and official Samsung firmware (.tar.md5 files). If they were surface-mounted, micro-soldering new clips (if available) onto the PCB pads might be necessary. Corrosion: Green or white residue on or around pads, indicating liquid damage. You'll need to remove screws and possibly metal shields to access the internal components. Vetting Tips: Rely heavily on seller ratings, detailed product descriptions, and explicit statements about part grade. In WhatsApp, go to `Settings > Chats > Chat backup` and ensure "Back up to Google Drive" is set to daily/weekly and a backup has recently completed. Use your magnifying glass to meticulously examine all connectors, flex cables, and components on the logic board for signs of oxidation. Embarking on a smartphone repair, whether for a cracked screen, a failing battery, or water damage, requires more than just mechanical aptitude; it demands the right set of tools. Inspect: After removing all visible adhesive and cleaning with IPA, use a magnifying glass to inspect the entire bonding surface for any remaining specks or oils. Cleaning: Gently clean around the buttons with a fine brush or a cotton swab dampened with isopropyl alcohol. If the input is present but there's no output, or the output is erratic, the IC is suspect. Drag an app icon across the entire screen, ensuring it follows your finger without skipping or freezing. OLED technology works by passing an electric current through organic materials, causing them to emit light. Non-Metallic Pick: Carefully use a thin, non-metallic object, like a wooden toothpick or a plastic dental pick. Look for bends, cracks, tears, or signs of corrosion (green/white deposits). Cleaning: If debris is present, use a non-conductive tool to gently dislodge it. This can damage the internal conductor or shield, leading to signal loss. Verify the Ethernet cable is good and connected to a working router/switch. Using a protective case and screen protector can prevent many external damages. Keep Your Phone Clean and Dry: Regularly wipe your screen and avoid using your phone with wet hands or in humid environments. Adhesive remover or high-concentration isopropyl alcohol (IPA): To clean off old adhesive residue. Trim Excess Wire: Carefully trim any excess jumper wire with precision tweezers or a scalpel. The hotspot connection itself might become unstable, experiencing frequent disconnections or difficulty maintaining a stable link to connected devices. LCD/OLED Displays: Never apply IPA directly to the display panel, especially along its edges.

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