How to fix Dell Latitude 7420 Not Charging

Dell Latitude 7420 Not Charging Repair

At Reformtech, we recently worked on a Dell Latitude 7420 that had completely stopped charging and refused to power on. The device was brought in by a local repair shop, and upon inspection, we discovered that the USB-C charger meter was not even turning on, indicating a deep power issue.

Diagnosing the Issue

1. Physical Inspection & Opening the Dell Latitude 7420
   • We started by opening the back cover, which was conveniently designed with captive screws that don’t fall out—a small but appreciated design choice.
   • With the laptop open, we suspected an issue with the charging port. Since this model has two USB-C charging ports, we tested both, but neither was functional.
2. Checking Main Power & Battery Voltage
   • The main power rail was checked, but the battery showed 0 volts—a clear indication that power wasn’t reaching the system.
   • We proceeded with unplugging the battery and testing for shorts on the main power rail.
   • Surprisingly, there was no short detected, making the issue even more complex.
3. Deep Board-Level Inspection
   • With the motherboard removed, we inspected the USB-C charging port connection. The design featured a secondary connector board, which linked to the main motherboard—a rather unusual setup.
   • Checking for blown components, we examined fuses, power rails, and key ICs. The power supply section had some inconsistencies, and a key power rail measured only 15 ohms, which was suspiciously low.

Identifying the Faulty Component

• The USB-C PD (Power Delivery) controller chip, TPS65992, was suspected to be faulty.
• Testing the circuit with a power supply revealed that a significant amount of current (1.3A – 2A) was being drawn, pointing towards a shorted component.
• After further analysis with a thermal camera, we confirmed that the TPS65992 chip was overheating, confirming it as the defective part.

Repair Process

1. Removing the Faulty TPS65992 Chip
   • Using flux and precise hot air soldering, we removed the burnt TPS65992 chip.
   • Post-removal testing showed that the short circuit was gone, further validating that the chip was the culprit.
2. Attempted Temporary Fix
   • Since this model had two TPS65992 chips (one for each USB-C port), we tried swapping the chip from the secondary USB-C port to test functionality.
   • Initially, the laptop started drawing power, indicating success, but after a few moments, the replaced chip also failed—suggesting it was already compromised before the swap.
3. Ordering New TPS65992 Chips
   • We sourced two brand-new TPS65992 chips from a reputable supplier to ensure reliability.
   • The new chips arrived two weeks later, and we proceeded with a clean installation.
4. Final Testing
   • After replacing both faulty TPS65992 chips, the laptop successfully powered on and began charging normally.
   • We monitored power draw and system performance to confirm a stable fix.

Conclusion

The Dell Latitude 7420 was successfully repaired by replacing the TPS65992 Power Delivery controllers, restoring full charging and power functionality. This case highlights the importance of diagnosing power rails, checking for shorts, and using thermal imaging to locate faulty components. If you’re experiencing charging issues with your laptop, visit Reformtech, your trusted laptop repair expert in Behala Chowrasta, Kolkata!

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