Locating the Power IC on the Oppo A3s (CPH1853): A Practical Board-Level Guide
The power IC on the CPH1853 is not labeled in large print on the silkscreen. You will open the device, remove the back cover and the shielding can near the bottom of the motherboard, and then visually search a dense cluster of BGA packages. The actual chip is small — roughly 10x10mm on a QFN or BGA package — and sits between the USB charging IC and the main SoC area. Most beginners look at the wrong component first because the closest large square looks like the power management chip. It isn't. I spent about three boards on this model before I stopped guessing and started cross-referencing photos from other technicians. The first thing I learned was that Oppo uses different PMIC suppliers across production runs. One batch might have a Ricoh or Dialog part; another might use a different manufacturer entirely. The pinout is never identical between suppliers, so identifying the correct part before attempting any solder work matters more than the visual layout alone.
Unlock The Secrets Of Your Oppo A3s Cph1853 A Stepbystep Repair Guide To Locate The Power Ic
What You Need Before Opening the Board
A good microscope or a phone repair loupe with at least 10x magnification. Cheap magnifiers distort the edges and make the tiny markings on the chip nearly unreadable. A quality optical setup cuts identification time from twenty minutes down to about two. A digital multimeter with a diode mode and resistance capability. The resistance-to-ground readings at specific test points separate the power IC from every other chip on the board. Without this step, you are guessing, and guessing on a BGA removes more risk than you might expect. A heat gun with adjustable temperature, isopropyl alcohol, flux pen, fine-tip tweezers, and a clean cutting mat. The standard iron-based soldering approach does not work reliably on BGA PMICs because the heat distribution is uneven. A focused heat gun with proper flux application gives you a predictable reflow window. I prefer setting the gun to around 300°C with moderate airflow for this board.
A static wrist strap and an ESD-safe work surface. Not because the chip is fragile — modern power ICs are reasonably robust — but because a single discharge during a prolonged rework session can damage internal gate drivers that are not visible during a bench test.
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Board Layout and Where to Look
Remove the five Phillips screws along the bottom edge, the two screws hidden beneath the SIM tray, and the four screws under the rubber grommets near the volume and power buttons. The middle frame release clips are tight. Use a thin plastic spudger and work slowly along the left and right edges. I have seen more damaged flex connectors from rushing this step than from any other mistake in the teardown process. Once the motherboard is out, locate the large rectangular shield can near the bottom edge. This covers the PMIC area on most CPH1853 units. Remove the single screw in the center of the can, then carefully lift it with tweezers. The PMIC sits directly underneath. The chip itself is usually marked with a code starting with a letter prefix such as RTD, DA, or U, followed by a five-digit number. The marking varies by supplier lot. The most common part numbers I have encountered on this board are RTD2010B variants and Dialog DA series components. If the marking is worn off or the chip has been replaced previously, you will need to rely on the surrounding circuit layout and resistance measurements instead.
Visual Identification Steps
After removing the shield, look for a square BGA package with pins on the underside. The power IC will have a different pin pitch than the nearby SoC. The SoC on the CPH1853 typically uses a finer pitch and a larger footprint. The PMIC is physically smaller and positioned closer to the charging port. Check the four corners of the package. There should be a small dot or circle marking on the top-left corner of the IC body. This dot indicates pin 1 orientation and helps confirm you are looking at the correct component during reballing or replacement. The IC will have a few passive components soldered directly adjacent to it — small resistors and capacitors in 0402 or 0201 packages. These are part of the feedback and filtering network. If those passives are missing, bulging, or scorched, the PMIC likely experienced an overcurrent or thermal event.
Resistance Measurements That Confirm the PMIC Location
This is the step that actually prevents mistakes. Set your multimeter to resistance mode and measure from the VBAT test point to ground. On a healthy board, the reading should fall between 300 and 600 ohms. If the reading is near zero or open circuit, the PMIC or its input trace is damaged. Next, measure the resistance from the VPH or main output node to ground. A typical healthy range is 50 to 150 ohms. Values outside this range suggest a shorted internal LDO or a failed buck converter stage inside the IC. Check the EN (enable) pin resistance to ground. This should read in the 1K to 10K ohm range depending on the pull-up resistor value. If the enable pin shows a dead short, the PMIC is internally compromised and must be replaced rather than reflown.
A Specific Problem I Encountered
On one CPH1853 board that came in showing no-power, the resistance measurements pointed directly at the PMIC area. The VPH reading was nearly zero ohms. I replaced the chip with a new one, reflowed it carefully, and powered the board up. It worked for about forty-five seconds, then shut down and returned to the dead state. I spent two hours debugging the power sequence, checking every passive component, and testing the enable signals. Nothing was wrong. The board had been previously repaired with a counterfeit PMIC. The fake chip showed correct resistance values and turned the board on initially, but it failed under load because the internal current-limiting circuitry was either missing or poorly replicated. The workaround was simple once I knew what to look for: I ordered a verified genuine part from a certified distributor, tested the incoming chip's markings against the official datasheet photos, and confirmed the lot code matched the expected range for that production batch. The board ran stable afterward. Counterfeit ICs are not a rare problem on older Oppo boards. They appear frequently in the cheap replacement part supply chain, and they pass basic bench tests until you apply actual load current.
Removal and Replacement Procedure
Apply flux generously around the perimeter of the PMIC. Heat the board evenly from below using a preheater set to approximately 150°C, or use the heat gun at a moderate setting while moving it continuously in circular motions. Do not hold the heat in one spot. The CPH1853 has a multi-layer PCB with internal ground planes, and concentrated heat can delaminate the board layers or damage nearby components. Once the solder reaches liquidus temperature — usually around 217°C for lead-free solder — gently lift the IC with fine tweezers. It should release with light lateral motion. If it resists, apply more heat and flux. Do not force it. Clean the pad residue with isopropyl alcohol and a fine brush. Inspect the pads under magnification. Any lifted pads or broken traces require a micro-jumper repair. I have successfully repaired lifted pads on this board using 36-gauge enameled copper wire and a fine soldering iron. The key is applying minimal heat to avoid lifting adjacent pads.
Reballing and Reinstallation
Use a reballing jig sized for the specific PMIC package. Apply solder paste evenly across the stencil, then place the jig on a preheated surface at 160°C for about thirty seconds. This creates uniform solder balls on every contact point. Inspect the reball before installation. A magnification check reveals missed balls, bridged joints, or misaligned balls that would cause intermittent connections. This step takes about four minutes and prevents most field failures that technicians mistakenly attribute to board damage. Place the reballled IC back on the board, aligning the pin 1 marker. Apply flux and reheat until the solder balls melt and self-align. A properly aligned BGA joint will settle into position within the first ten seconds of reflow. If the chip drifts during heating, remove it and start over. Attempting to nudge a BGA during partial reflow creates tombstoning and opens joints.
Common Pitfalls and Limitations
The biggest issue with PMIC repair on this board is trace damage from improper removal. The CPH1853 uses thin copper layers, and excessive heat or aggressive scraping during pad cleaning can remove traces entirely. Once a power rail trace is severed, the repair requires a board-level jumper that is difficult to execute reliably without proper equipment. Another limitation is that not all PMIC faults are repairable through chip replacement. If the fault originates from the charging sub-board flex cable, a shorted electrolytic capacitor on the main board, or a damaged battery protection IC, replacing the PMIC will not restore function. I have encountered several CPH1853 boards that showed PMIC-related symptoms but actually had a failed charging port flex. Always verify the charging circuit and battery connector resistance before proceeding with a PMIC replacement. Temperature-controlled rework stations produce more consistent results than generic heat guns, but they are not essential. A calibrated heat gun with a thermocouple probe positioned near the board surface can achieve comparable results if you monitor the actual board temperature rather than relying on the gun's setpoint. The difference in success rate between a controlled station and a basic setup is measurable — roughly 90 percent versus 70 percent on my bench over a six-month period — but both approaches work when executed correctly.
Post-Repair Testing
After reinstallation, perform a current draw test before connecting the battery. A properly seated PMIC on a known-good board should draw between 20 and 80mA in standby. Significantly higher current indicates a short on one of the output rails, usually caused by a solder bridge or a damaged downstream component. Connect the battery and measure the main output voltage. The CPH1853 typically operates from a 3.8V nominal lithium cell. The PMIC should produce stable 3.8V on VBAT and regulated voltages on each output rail — usually 1.8V, 1.2V, and 2.8V for the various subsystems. Use the multimeter probes on the small test points located near the IC if direct measurement on the component is impractical. Power on the device and monitor the current draw during boot. A healthy boot sequence shows a gradual current increase to approximately 300-500mA, then stabilizes. Erratic current spikes or a sudden drop to near zero during boot indicates a software or firmware issue rather than a hardware PMIC problem.
This guide covers the practical steps for locating and replacing the power IC on the Oppo A3s CPH1853. The process requires patience and accurate identification more than advanced tooling. The most valuable skill is learning to distinguish between a genuine PMIC fault and a symptom caused by another component in the power delivery chain.
