[SOLVED] I'm looking for Verykool i720 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Verykool i720. 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.

@Nitin

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 Verykool i720 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/unlock-code.220292/
Take a look at comment #226
Also, this : https://www.ifixit.com/Answers/View/430462/Lumia+1520+Turn+off+and+Never+Boot+again.
You can also check this video starting from minute 2:

The Verykool i720 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 Verykool i720 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 Verykool i720 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 Verykool i720 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/104538/I+cannot+open+applications

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

Find the Hot Spot: As current flows through the shorted component, it will heat up. Open Device: Depending on the model, this might involve heating and carefully prying open the screen or the back cover. Discharge battery: For safety, discharge the battery below 25% before starting work. Cons: Requires advanced soldering equipment (hot air station, microscope) and a high level of skill. Whether people can't hear you during calls, voice assistants ignore your commands, or videos lack sound, a defective microphone needs prompt attention. Misalignment: Ensure the flex cable is seated perfectly straight and fully within its connector. In conclusion, replacing the main SoC on a smartphone logic board is a testament to the extremes of micro-soldering. Optical Image Stabilization (OIS): A mechanical system that shifts the lens or sensor to counteract handshakes, leading to sharper images and smoother videos. With careful diagnosis, precise micro-soldering techniques, and an understanding of the risks involved, experienced technicians can restore these vital sensors, breathing new life into a malfunctioning smartphone and returning full functionality to its motion-aware features.## 7. Factory Reset (Last Resort Software Step): If all else fails on the software front, a factory reset might resolve deep-seated software corruption. The immediate and most important action upon encountering a "moisture detected" warning is to stop charging the phone immediately and power it off. Verify that the APN settings for both SIMs match those provided by their respective carriers. A lower-energy ESD event might partially damage a component without causing immediate failure. Could be a short circuit created during rework, or damage to another critical component due to excessive heat or improper handling. Sometimes, a simple factory reset can resolve software-related audio glitches. Ensure it's flat, aligned correctly, and doesn't obstruct any moving parts or electrical contacts. Insert your SIM ejector tool straight into the small hole next to the SIM tray. By systematically isolating variables and cross-referencing observations, the true source of the charging instability can be identified, leading to an effective resolution and restoring reliable power to your device.4. A significantly degraded capacity (e.g., below 80%) often correlates with percentage inaccuracies. Does the compass needle track smoothly and accurately? Repeat this in different physical locations, especially away from any potential sources of interference. It's essentially your phone's fingerprint on a mobile network, used to identify individual devices. Physical Location: Helps you quickly find the physical component on the board that the schematic refers to. However, a successful repair can save a device that would otherwise be deemed unrepairable, making it a highly rewarding endeavor for experienced technicians. Missing/Broken Pins: While less common for the entire pin to be missing, check for any visible breaks or if a pin appears to be pushed back into the connector housing. In dedicated sensor testing apps, a malfunctioning barometer might show no data at all, or abnormally high or low-pressure readings that deviate significantly from local, known conditions. Physical Damage: Drops or impacts can dislodge or damage the motor or its connections. Gathering the right tools beforehand will make the cleaning process safer and more effective. Once the solder melts, gently lift the old IC using fine-point tweezers or a vacuum pickup tool. If, after these thorough evaluations, the evidence strongly suggests a faulty battery temperature sensor, the likely solution involves hardware repair. While standard lead-free solders (e.g., Sn/Ag/Cu alloys) are common, their high tin content makes them susceptible to gold embrittlement.

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