[SOLVED] I'm looking for At t Mustang repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my At t Mustang. 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.

@Onur

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 At t Mustang 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/856406/The+clip+at+the+top+of+keyboard+button+is+Broken.
Take a look at comment #1084
Also, this : https://xdaforums.com/t/re-allocating-buttons-for-use-in-games-etc.218537/.
You can also check this video starting from minute 3:

The At t Mustang 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 At t Mustang 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 At t Mustang 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 At t Mustang 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/Guide/Sony+Cyber-Shot+DSC-W170+Top+Panel+Replacement/167124

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

Software updates often include bug fixes for hardware components like the flashlight. Forgetting to Transfer Small Parts: Some modules may have tiny plastic button covers or gaskets that need to be transferred to the new part. Microscope and Experience: Work under a stereo microscope to ensure precise heat application and observe solder reflow. Factory Reset: As a last resort for software-related issues, a factory reset (after backing up all data) can rule out deep-seated software conflicts or corruptions. It's adhesive on one side, and the other side is conductive (single-sided conductive adhesive is preferred, ensuring the adhesive side is non-conductive and the copper/aluminum side is conductive). Processing and Matching: The captured image, representing the unique fingerprint pattern, is then processed by the phone's secure enclave and compared to stored fingerprint templates for authentication. This allows for different encryption keys for different data, enabling features like direct boot (where certain system data is accessible before unlock) while keeping user data highly secure until the device is unlocked. A significantly lower reading might indicate a short, and "OL" might indicate an open circuit. Observe Solder: Keep a close eye on the solder joints through the microscope. This can stem from either software corruption or underlying hardware problems. Sensor Cleaning Swabs (Last Resort): If blowing doesn't work, specific sensor cleaning swabs designed for DSLR camera sensors can be used. Misaligned or loose screws can create gaps, allowing dust and moisture to penetrate and damage sensitive internal electronics. Try disabling adaptive brightness, eye comfort shield (blue light filter), dark mode, or any other display enhancements one by one to see if they are contributing to the issue. Missing or Loose Screws: If the motor is screw-mounted, check that all retaining screws are present and tightly fastened. This is the first and most fundamental step to prevent electrical hazards and component damage. It's a repair best left to highly experienced technicians with specialized equipment. Delicate Integrated Circuits (ICs): Many smartphone repairs involve replacing or reballing BGA (Ball Grid Array) ICs. If the problem persists with a different SIM, it points more strongly towards your phone’s hardware or software. Test: Temporarily re-connect the camera module and battery, then power on the phone to take test photos. Stand: A sturdy boom stand or articulated arm provides flexibility in positioning the microscope over the board and allows for viewing larger areas. Excessive Heat: The phone or charging pad becomes unusually hot during charging. Apply new adhesive around the perimeter of the new housing where the screen sits. An advanced approach involves a combination of specialized tools, systematic analysis, and a deep understanding of circuit design. Use a suction cup and opening picks to carefully separate the display/back cover from the frame. Improper Previous Repairs: The flex cable can be pinched, torn, or improperly reconnected during other repairs (e.g., screen replacement). ESD: Although less sensitive than motherboard ICs, electronic components can still be damaged by static discharge. Power Off: Always power off the phone and disconnect the battery before working on the logic board. Visual inspection: Look for liquid damage or physical damage around the headphone jack or DAC area. Air Dry: Place all cleaned components on a lint-free paper towel in a warm, dry, well-ventilated area for at least 24-48 hours. This meticulous approach not only ensures that your spare parts remain viable for future repairs or resale but also reflects a professional and responsible attitude towards electronic waste and resourcefulness.

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