[SOLVED] I'm looking for TELSDA T138 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my TELSDA T138. 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.

@Jake

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 TELSDA T138 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/793686/My+ringer+does+not+ring.+I+have+a+I+PHONE+12+MINI.+CAN+IT+BE+FIXED
Take a look at comment #548
Also, this : https://www.ifixit.com/Guide/General+Pipe+Cleaners+Drain+Cleaner+PMEBO+2016+Reverse+Switch+Replacement/137379.
You can also check this video starting from minute 8:

The TELSDA T138 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 TELSDA T138 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 TELSDA T138 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 TELSDA T138 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/q-annoying-notification.3049685/

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

This guide will provide a comprehensive walkthrough, enabling you to restore clear and private call audio to your smartphone. Sometimes, adding a tiny blob of solder or ensuring the screw itself is clean can restore continuity. Adhesive Strips: If your phone's back cover or screen relies on adhesive for reassembly and water resistance. These delicate parts must be carefully transferred from the old screen to the new one. Consult a Teardown Guide: Find a step-by-step guide for your specific phone model (e.g., iFixit) to learn how to safely open it and locate the power button flex cable. Network/Internet Connection: For cloud-based voice recognition (most modern systems), a stable internet connection is crucial. Try a known-good, high-quality cable and a different charging adapter. Relevance: Extremely popular in smartphone repair, especially for BGA reballing and IC replacement. Apply new adhesive (either pre-cut adhesive strips or a thin bead of B-7000 glue around the perimeter). When a fingerprint sensor malfunctions, it can be a significant inconvenience, forcing users back to less convenient methods like PINs or patterns. The advantages of using a thermal camera over a multimeter for short circuit diagnosis are manifold. Download Files: Place the flashable ZIP files (for kernel or drivers) onto your phone's internal storage or an SD card. This requires specialized tools like NAND programmers or specific data transfer devices (e.g., baseband EEPROM programmers for iPhones). It requires precision, patience, and the right tools, as improper handling can lead to further complications, especially with the sensitive proximity sensor. Localized Dimming/Dark Spots: Specific areas of the screen are dim or dark, suggesting issues with a section of the LED array. Check basic functions: display lights up, touch works, phone boots to the OS. Alignment is Key: Visually ensure perfect alignment before applying pressure to mate any connector. This often requires opening the phone and replacing the charging port sub-assembly. To inspect for burn-in, the most effective method is to display full-screen solid colors. Corrosion Evidence: Check the charging port, headphone jack, and SIM/microSD card slots for green, white, or blue crystalline deposits, which are tell-tale signs of corrosion. High-Magnification Microscope or Magnifying Lamp: Non-negotiable for precision and inspection. Nearby Inductors/Coils: Look for damaged or missing inductors (coils) near the sensor. Correct Tapping Position: The NFC coil has a specific location on your phone. As the battery degrades, gases can build up inside, causing the battery to expand. If there's no reaction, or if the reaction is inconsistent, the Hall sensor or its connection is likely faulty. Understanding what burn-in is, why it occurs, and how to troubleshoot or mitigate its effects is crucial for smartphone users and repair technicians alike. Re-test: After moving to a clear environment and removing accessories, re-test your compass app. After the shield has cooled, clean the entire area thoroughly with isopropyl alcohol and a soft brush to remove all flux residue. The preheater raises the board's temperature uniformly, reducing thermal stress, while the top heater melts the solder balls directly under the IC. Liquid Damage: Corrosion is a very common cause, as the tiny mic port can allow liquid ingress.

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