P3 Flight Controller aka MC repair

Table of Contents

Introduction
Symptoms
Common repair steps
Specific repair steps

Introduction

This page will guide you through component-level diagnosing and repair of the P3 Flight Controller board.

Most of the steps discussed here will require either skill or equipment which is not common. Basic knowledge of electronics is required to be able to follow this guide.

Symptoms

Most straightforward symptoms of an issue within P3 Flight Controller board are when mobile app shows error of a sensor which is located within the flight controller - IMU (gyroscope/accelerometer) error or barometer error. Many other errors may also be caused by FC, because it collects data from all other components. Ripped off pad or oxidated connection on the FC board may lead to all kinds of errors. When a flight controller MCU is completely dead, all four ESC units will start beeping (using motors as speakers), and connecting the drone to USB will not create a serial port device.

Common repair steps

Several universal steps should be taken when performing a component level repair. They should be skipped only if the nature of the symptoms rules out issues in related parts.

Inspect the board visually

Look at each chip on the board, using some kind of magnification if you can (microscope is best).

Look for a components with melted or fragmented cover.

Wherever possible, look at the pins and pads around each component. Search for irregularities, missing pins, corrosion, oxidation, circuit breaks.

If any of the components looks suspicious, check its function on a schematic and make it a priority for verification.

Specific repair steps

IMU errors

These can be caused by:

• Faulty power delivery to IMU board
• The sensor MEMS chip failure
• Faulty connection between IMU board and FC board
• Faulty soldering of the FC MCU

Faulty power delivery to IMU board

The IMU board is powered from a step-down converter on the FC board. Make sure voltage is properly propagated, and capacitor near the IMU chip is good (see schematics for details).

The sensor MEMS chip failure

In case of IMU element stuck, try opening the black plastic cover and tapping the metal case inside. The shock will usually unblock the MEMS sensors inside.

If any IMU error persists, try removing the IMU box completely, then open the metal case and put the IMU board to an ultrasonic cleaner with IPA.

If this won't help, measure RC components on the IMU board to check if they're good (see schematics for comparison), and reflow all solder joints (heat up to liquidify).

Finally, replace the MEMS chip.

Faulty connection between IMU board and FC board

The connector may either have oxidated contacts, or be incorrectly soldered. Clean the contacts it with IPA or other alcohol. Measure resistance of all the connections. Reflow the solder on pads (heat up to liquidify).

Faulty soldering of the FC MCU

This is unlikely to happen, but possible. If the problem persists after replacing the IMU board completely, then FC MCU soldering may be the cause.

If you're skilled enough, try reflowing or rebailing the FC MCU. Replacing will not work, because the micro-controller contains a DJI loader which is required for FC firmware to work.

Barometer errors

These are often caused by a little dust inside the barometer, but may be also caused by bad soldering.

Find the barometer at bottom of the FC board by checking schematics. Ultrasonic the FC board in IPA, then reflow the barometer. Also check if it is properly powered.

If this won't help, replace the barometer - it is easy to find replacement. You will need a hot air station for reflowing and replacing.

If the issue persists after replacing barometer, re-check its the step-down regulator which powers it. If power is good, then issue is caused by bad communication to FC MCU. If you're skilled enough, try reflowing or rebailing the FC MCU.

FC MCU not starting

The micro-controller may not be starting either because its dead, or because it is not powered.

Start by checking voltage on all power pads. If any of the voltages is missing, fix a corresponding regulator (see schematics for details). While replacing regulators, make sure that their output is not shorted, otherwise they will get damaged again. You may also use external voltage source to check whether restoring power to the faulty line brings the FC back to life.

When the FC MCU is powered and not damaged, it will provide a serial interface with startup logs on the USB output - this is the simplest way to check whether MCU starts, even when it is not connected to ESC Center Board.

Damaged regulators on the FC board usually suggest that its 3V6 input was shorted to battery (15V). In such a case, almost all chips of the FC board will be fried.