[SOLVED] I'm looking for HTC Desire 620 repair guide or schematics (free) - Phones & Tablets Forum

Hi,

I'm hoping you can help me out with my HTC Desire 620. 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.

@Camilo

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 HTC Desire 620 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/Guide/Novatel+MiFi+2+4G+LTE+Hotspot++Battery+Replacement/114272
Take a look at comment #1084
Also, this : https://www.ifixit.com/Answers/View/819160/Your+PC+ran+into+a+problem+and+need+restart,we'll+restart+for+u.
You can also check this video starting from minute 6:

The HTC Desire 620 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 HTC Desire 620 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 HTC Desire 620 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 HTC Desire 620 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/683824/which+charger+cable+fits+the+ipad4+-+model+A1458

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

As you inject voltage, the shorted component will melt the rosin or cause the freeze spray to evaporate quickly, revealing itself as the hot spot. Side Buttons (Power, Volume): These might be part of a small flex cable assembly that needs to be removed from the frame. Beyond simple voltage conversion, the PMIC integrates several crucial functions: Calculate the average angular velocity for each axis over the entire logging period. Using your plastic spudger, tweezers, and a lint-free cloth or cotton swabs dampened with IPA, meticulously remove all traces of the old adhesive from both the phone's frame and the underside of the display assembly. Motherboard Connector: Check the connector on the motherboard for bent pins, debris, or corrosion. Apply a tiny, controlled amount of plastic-compatible epoxy or super glue (e.g., Loctite Plastics Bonding System, or a very small dab of two-part epoxy like JB Weld Plastic Bonder) into the stripped hole. Cotton Swabs/Q-Tips: Indispensable for applying solvent and cleaning intricate crevices. Each of these modules communicates with the main system-on-chip (SoC) or other controllers via various serial protocols like I2C, SPI, UART, and high-speed interfaces like MIPI. Bent Pins: Check the pins within the connector on both the motor's flex cable and the logic board for any bends, breaks, or corrosion. Pre-Existing Functionality: Note any components already not working (e.g., "camera not focusing," "charging port loose," "volume buttons unresponsive"). Field Test Mode (iOS) / Network Signal Info Apps (Android): As mentioned in the 5G evaluation, these tools can show you which specific band your phone is currently connected to. Microscope: Absolutely essential for working with tiny components and BGA pads. Pay extra attention to corners and areas around camera cutouts, buttons, and sensors, where a strong seal is needed. Preventing Pollution: Keeping heavy metals (like cobalt, nickel, manganese) and toxic electrolytes out of landfills and waterways. Image Quality: Take a test photo and video with both front and rear cameras. While often overlooked, the proper functioning of this mechanism is essential for detecting and securely holding your SIM card, which in turn enables cellular connectivity. In a market flooded with various options, distinguishing between genuine (OEM - Original Equipment Manufacturer), original refurbished, high-quality aftermarket, and low-grade counterfeit parts can be a daunting but critical task. Diagnosing the root cause can range from a simple software glitch to a complex hardware fault requiring micro-soldering. Go to Settings > System > Reset options > Erase all data (factory reset). Precision and Control: The glue remains liquid indefinitely until exposed to UV light, allowing for precise application, positioning, and repositioning without the rush associated with fast-setting glues. Razor Blade (EXTREME CAUTION): Use only as an absolute last resort, with a very shallow angle, and only on robust metal frames, never near flexible cables or delicate plastic. Controller Damage: If the internal controller of the eMMC/UFS chip itself was damaged by liquid, it might not respond to the reader, or might present corrupted data. Branding/Markings: Compare any logos or part numbers to genuine components. Ensure it sits flush and covers the entire sealing surface without any wrinkles or gaps. This guide provides an overview of the technical process, but it is incumbent upon the reader to ensure their actions are compliant with all local laws and regulations. If after all these diagnostic steps, your phone's battery life remains poor, especially if you suspect a hardware issue or if you're uncomfortable performing a factory reset or opening your device, it's time to consult a professional repair service or your phone manufacturer. Backlight Coil (Inductor): This component works in conjunction with the backlight IC to store and release energy, stepping up the voltage. Solder Joint Issues: Cold solder joints, lifted pads, or solder bridges (short circuits between pads) are common under ICs. Three-digit code (e.g., 102): The first two digits are the significant figures, the third is the multiplier (number of zeros).

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