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If PCA9685 is your project decision, I would recommend to refer to MagPi84 Circuit Python servo tutorial and use AdaFruit's open hardware/software PCA9685 PWM Controller HAT, and quad servo HAT, and their python servo libraries.

 

My servo project here is inspired by them. Please see Reference (2) for more details.

If PCA9685 is your project decision, I would recommend to refer to MagPi84 Circuit Python servo tutorial and use AdaFruit's open hardware/software PCA9685 PWM Controller HAT, and quad servo HAT, and their python servo libraries.

My servo project here is inspired by them. Please see Reference (2) for more details.

/ to continue, ...

Rpi4B PCA9685 PWM Controller driving 4 TowerPro MG996R Servos - tlfong01

PCAS9685 PWM Controller Installation Notes - tlfong01

Rpi3B+ GPIO PWM Servo Testing Notes - tlfong01

Your Rpi3B+ log file shows DMA channels are use to PWM control servo. But the Rpi4B log file shows PCA9685 PWM GPIO is replacing DMA PWM. You need to show your program list to confirm this.

If PCA9685 is your project decision, I would recommend to refer to MagPi84 Circuit Python servo tutorial and use AdaFruit's open hardware/software PCA9685 PWM Controller HAT, and quad servo HAT, and their python servo libraries.

My servo project here is inspired by them. Please see Reference (2) for more details.

(1) Rpi4B PCA9685 PWM Controller driving 4 TowerPro MG996R Servos - tlfong01

(2) PCAS9685 PWM Controller Installation Notes - tlfong01

(3) Rpi3B+ GPIO PWM Servo Testing Notes - tlfong01

(3) tlfong01's Rpi4B Quad I2C Bus Testing Program Listing

# fi2c62.py  tlfong01 2019aug28hkt1433

from time          import sleep
import             smbus
import             fprint53    as fprint
import             ftime53     as ftime

# I2c Bus Setup Notes
# pi@raspberrypi:~ $ date Wed 28 Aug 2019 03:26:24 PM HKT
# pi@raspberrypi:~ $ uname -a
# Linux raspberrypi 4.19.58-v7l+ #1245 SMP Fri Jul 12 17:31:45 BST 2019 armv7l GNU/Linux
# pi@raspberrypi:~ $ sudo nano /boot/config.txt
# dtoverlay=i2c1,pins_2_3  (board pins 3, 5)
# dtoverlay=i2c3,pins_4_5  (board pins 7, 29)
# dtoverlay=i2c4,pins_6_7  (board pins 31, 26)
# dtoverlay=i2c5,pins_12_13 (board pins 32, 33)
# dtoverlay=i2c6,pins_22_23 (board pins 15, 16)
# pi@raspberrypi:~ $ ls /dev/i2c*
# /dev/i2c-1  /dev/i2c-3  /dev/i2c-4  /dev/i2c-5  /dev/i2c-6

# ********************************************************************************
# ********************************************************************************

# *** I2c Bus Config ***

i2cBus1 = smbus.SMBus(1) 
i2cBus3 = smbus.SMBus(3)
i2cBus4 = smbus.SMBus(4)
i2cBus5 = smbus.SMBus(5)

i2cBusDict = {'I2cBus1': i2cBus1,
              'I2cBus3': i2cBus3,
              'I2cBus4': i2cBus4,
              'I2cBus5': i2cBus5,
             }

# *** Pca9685 I2c Slave Device Congif ***

pca9685DevAddrDict = {
                'Dev0': 0x40,
                'Dev1': 0x41,
                'Dev2': 0x42,
                'Dev3': 0x43,
                'Dev4': 0x44,
                'Dev5': 0x45,
                'Dev6': 0x46,
                'Dev7': 0x47,
              }

pca9685RegAddrDict = { 'Mode1': 0x00,
                       'Mode2': 0x01,
                     }

pca9685DataByteDict = {
                       'Mode1Reset': 0x11,
    
    }

# ********************************************************************************
# ********************************************************************************

# *** Read Write Print Device/Register Functions ***

def writeDevTwoBytes(i2cBus, devAddr, writeByte1, writeByte2):
    i2cBus.write_byte_data(devAddr, writeByte1, writeByte2)
    return

def writeRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName, writeByte):
    devAddr = devAddrDict[devName]
    regAddr = regAddrDict[regName]
    writeDevTwoBytes(i2cBus, devAddr, regAddr, writeByte)
    return

def readDevOneByte(i2cBus, devAddr, readByteAddr):
    readByte = i2cBus.read_byte_data(devAddr, readByteAddr)
    return readByte

def readRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName):
    devAddr = devAddrDict[devName]
    regAddr = regAddrDict[regName]
    readByte = i2cBus.read_byte_data(devAddr, regAddr)
    return readByte

def printRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName):
    readByte = readRegOneByte(i2cBusName, devAddrDict, devName, regAddrDict, regName)
    print(printTitle, hex(readByte))
    return
    
# *** Main Test Function ***

def testWriteReadPca9685Bus1Dev0RegMode1():     
    fprint.printBeginExecFunction()

    i2cBusName = 'I2cBus1'
    devName    = 'Dev0'
    regName    = 'Mode1'
   
    #i2cBus      = fi2c.i2cBusDict[i2cBusName]
    i2cBus      = i2cBusDict[i2cBusName]
    devAddrDict = pca9685DevAddrDict
    regAddrDict = pca9685RegAddrDict  
 
    writeByte = 0x77
    
    writeRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName, writeByte)
    readByte = readRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName) 
    
    if readByte == writeByte:
        resultsString = 'Good'
    else:
        resultsString = 'Bad'

    devAddr = devAddrDict[devName]
     
    fprint.printTitleOneByteNum('PCA9685 I2C Address',             fprint.indentFormat640, devAddr)
    fprint.printTitleOneByteNum('PCA9685 MODE1 Register Written',  fprint.indentFormat640, writeByte) 
    fprint.printTitleOneByteNum('PCA9685 MODE1 Register Read',     fprint.indentFormat640, readByte)    
    fprint.printTitleString('Write/Read Results',                  fprint.indentFormat640, resultsString)
 
    fprint.printEndExecFunction()
    return

def testPingPca9685Bus1Dev0RegMode1():     
    fprint.printBeginExecFunction()
    
    i2cBusName = 'I2cBus1'
    devName    = 'Dev0'
    regName    = 'Mode1'
   
    #i2cBus      = fi2c.i2cBusDict[i2cBusName]
    i2cBus      = i2cBusDict[i2cBusName]
    devAddrDict = pca9685DevAddrDict
    regAddrDict = pca9685RegAddrDict
    
    devAddr = devAddrDict[devName]
    
    readByte = readRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName)    

    compareByte = pca9685DataByteDict['Mode1Reset'] 
    
    if readByte == compareByte:
        resultsString = 'Good'
    else:
        resultsString = 'Bad'
        
    fprint.printTitleString('PCA9685 I2C Address',             fprint.indentFormat640, hex(devAddr))
    fprint.printTitleString('PCA9685 MODE1 Register Written',  fprint.indentFormat640, hex(compareByte)) 
    fprint.printTitleString('PCA9685 MODE1 Register Read',     fprint.indentFormat640, hex(readByte))    
    fprint.printTitleString('Ping Results',                    fprint.indentFormat640, resultsString)
 
    fprint.printEndExecFunction()
    return
   
# ********************************************************************************
# ********************************************************************************

# *** Main Tests ***

def mainTests():
    #ftime.testPrintDateTime()
    testPingPca9685Bus1Dev0RegMode1()
    testWriteReadPca9685Bus1Dev0RegMode1()
    return
    
# ********************************************************************************
# ********************************************************************************

# *** Init/Main Functions ***

# *** Init Function ***

def init():
    pass
    return

#*** Main Function ***

def main():
    init()
    mainTests()    
    return

# ********************************************************************************
# ********************************************************************************

# *** Main ***

if __name__ == '__main__':
    main()

# *** End of Program ***

# ********************************************************************************
# ********************************************************************************