[SOLVED] I'm looking for Unknown HC 800 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my Unknown HC 800. 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.

@Stefanie

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 Unknown HC 800 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/oneplus-soft-bricked-only-hang-on-logo-data-are-most-important-please-guide.3590332/
Take a look at comment #1252
Also, this : https://www.ifixit.com/Answers/View/315455/power+window+not+working+door+lock+either.
You can also check this video starting from minute 8:

The Unknown HC 800 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 Unknown HC 800 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 Unknown HC 800 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 Unknown HC 800 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/n-ext-update-is-bringing-gestures-and-other-improvements.3869095/

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

This includes the display driver IC, the backlight driver circuit, and associated components (coils, capacitors, diodes) or traces. Always ensure the battery packaging is intact and free from moisture, as even trace amounts can initiate degradation over time. Identify High Drain: If the current draw remains consistently high (e.g., 100mA or more) even in standby, you have a leakage issue. A loose headphone jack can be an incredibly frustrating issue for smartphone users who rely on wired audio for music, calls, or other media. It's crucial to understand that achieving factory-level water resistance in a DIY setting is extremely challenging, but restoring splash resistance is often achievable. Manufacturing defects, though rare, can also contribute if the mesh material is unusually porous or poorly secured, allowing debris to enter more easily. Running these tests can help identify if a specific hardware component is outright failing, which can then be cross-referenced with your observed symptoms. Power Off Completely: Hold the side button and volume down (or just side button for older models) until the "Slide to Power Off" slider appears. Full baseband replacement on iPhones is exceedingly rare and generally involves specialized tools for data transfer from the old chip to the new, if even possible. Check Network Connectivity: Ensure your computer has a stable internet connection and can communicate with Apple's update servers. Understanding and analyzing thermal throttling helps you manage your phone's performance expectations and ensures its longevity.### 8. If the issue persists, flashing the stock firmware can address corrupted system files that might be misinterpreting sensor data or managing thermal profiles incorrectly. Example: If using jumper cables, connect the battery to one end of the multimeter (e.g., red probe), and the other end of the multimeter (black probe) to the phone's positive battery terminal. Submerge the entire logic board (without battery or other non-waterproof components) in a shallow tray of 99% IPA for a few minutes. In some less common scenarios, if the device heavily relies on the magnetometer for screen auto-rotation decisions, this function could also be impacted, though this is more typically governed by the accelerometer and gyroscope. Correct Voltage: Never exceed the maximum voltage of the phone's battery. Static Discharge: Always use an anti-static wrist strap or mat to prevent static electricity from damaging sensitive components. Other symptoms include intermittent vibration, very weak vibration that is barely noticeable, or a strange buzzing, rattling, or grinding noise during vibration, which often indicates a mechanical failure within the motor itself or a loose motor. Too much heat can damage components; too little can make separation difficult or lead to cold solder joints during rejoining. These facilities dismantle devices, safely extract hazardous materials, and recover valuable metals. Practice: If you're new to this, consider practicing on an old, non-functional device to get a feel for the connectors. Power off both your phone and the problematic Bluetooth accessory, wait a minute, then power them back on. Liquid Damage: Corrosion from water or other liquids can damage the chip itself, its surrounding passive components, or the traces on the PCB. Reconnect the Display Assembly (if previously detached): If you fully detached the display, carefully reconnect its flex cables to the logic board. Software Check: Rule out software issues by performing a factory reset or booting into safe mode, if applicable. Reconnect Battery: Reconnect the battery flex cable, ensuring it snaps securely into place. These cables typically consist of a central conductor, an insulating dielectric layer, a braided metal shield, and an outer insulating jacket. This distortion can manifest in various ways, from crackling and static to robotic voices, dropped syllables, or a complete breakdown of speech clarity. Standard Phone Repair Tools: Screwdrivers, plastic prying tools (spudgers), suction cup, heat gun/hair dryer. Liquid damage leading to corrosion around speaker terminals could also potentially interfere with signal flow in a way that mimics a polarity reversal, though this is less common than simple miswiring.

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