[SOLVED] I'm looking for Celkon A75 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Celkon A75. 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.

@Klaus

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 Celkon A75 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/error-with-samsung-ativ-s.3315468/
Take a look at comment #290
Also, this : https://www.ifixit.com/Answers/View/752730/Bluetooth+LED+remains+on+even+when+powered+off,+drains+battery..
You can also check this video starting from minute 6:

The Celkon A75 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 Celkon A75 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 Celkon A75 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 Celkon A75 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://xdaforums.com/t/need-screen-lock-app-for-note-7.3445609/

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

Plastic Cement/Epoxy: A strong, plastic-compatible adhesive (e.g., specialized plastic cement, two-part epoxy, or even B7000 glue if space is very tight) for securing salvaged anchors or creating a new mounting point. A healthy sensor will show a gradual increase in temperature during fast charging, followed by a stabilization or slight decrease as it approaches full charge. Good ambient lighting is also important; while testing with a dimmed room can make some defects more obvious, it's beneficial to test in various lighting conditions. Reconnect the Battery: Carefully snap the battery flex cable back into its connector on the logic board. To successfully replace a smartphone microSD card slot, you'll need a collection of specialized tools and a new component: Smartphones are held together by tiny screws of various types and sizes. Safety Glasses: Protect your eyes from any flying debris or solvent splashes. Replacing a faulty proximity sensor is a common repair that requires careful disassembly and attention to detail. Backup Data: Always create a full backup of your phone's data before attempting any hardware repair. Excessive wind noise: The foam might not be dense enough or not properly seated. This can be done by dipping the board in a separate container of IPA or deionized water, or ideally, with another short cycle in the ultrasonic cleaner filled with pure IPA or deionized water to ensure all foreign substances are completely removed. Pop Connectors: Less common, but some components (like main flex cables) might have larger connectors that directly plug in. Enhanced GPS Accuracy: Assisting GPS systems to quickly determine vertical position, improving overall location accuracy. Shielding Cans: The metal shielding cans covering various ICs are typically soldered to ground. Cracked Glass: While the display might still show an image, a cracked glass surface typically means the digitizer layer beneath it is also compromised. Common mistakes include using too high a temperature, which can scorch the board or damage the IC; using too much airflow, which can blow away surrounding components; not using a preheater, leading to thermal shock and a need for excessive top heat; and applying force before the solder is fully molten, resulting in lifted pads. Bloatware Removal: Uninstall pre-installed, non-removable system applications (bloatware) from carriers or manufacturers that often consume resources and space. Carefully open the phone according to a reliable teardown guide for your model. Known Good Battery: For comparison and testing if the phone's original battery is suspect. Description: These are black or white adhesive strips with tabs that extend from under the battery. Stray Debris: Use a flashlight to check for any leftover tools, small screws, or debris inside the device before sealing it. Data on your phone will likely be lost during most recovery procedures, so if you haven't backed up, this is an unfortunate consequence. Each notification can wake your screen and trigger background processes. Ensure they are correctly oriented according to the tray's cutouts and markings. Apply hot air in a controlled, circular motion over the entire surface of the DSP. Third-party apps like AccuBattery can provide estimates (though less accurate than internal diagnostics). They are connected to internal copper traces (thin electrical pathways) that route signals and power throughout the board. Screen Removal: For most gaming phones, the display is the primary access point. Avoid strong, direct blasts into the button, which could push debris further in or damage internal components. Evaluating smartphone wireless hotspot problems requires a systematic approach, checking configurations on both the host smartphone and the client device, as well as considering the cellular network conditions.

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