Focusrite Scarlett USB audio interface #
This page will focus (!) mostly on the 3rd generation Scarlett 4i4.
Repairs #
It seems a very common failure mode is for the 3.3V regulator to fail short (sending 5V where it shouldn’t), which damages parts of the CPU including usually its USB peripheral. Symptoms include:
- device not enumerating
- front panel unresponsive (sometimes the 48V button behaves normally)
- OS reporting overcurrent condition
Disassembly #
There are only two screws holding the inner “tray”, of course hidden underneath the rear rubber feet.
Main components #
- U27 XMOS XU216-256-TQ128
- U1,7 NJM2122
- U2,4,6,9,11,12,14-17 NJM8065
- U10,13 HEF4052 analog switch
- U8 HEF5053 analog switch
- U18 LD1117AG
- U19 LTV-356T opto
- U20,21 CS4272 codec
- U22? “BEV”* MP2181 buck reg for +1V
- U24 “2PCC”, CS2000 clock gen
- U25 “VEA”* , sot-143 4pin : probably CAT811 voltage supervisor. Unknown thresh voltage
- U28 “5K” or “40” (random), ??QFN-12 2x2mm, headphone amp. Not AD/MAX, onsemi, TI, NJM, nxp, renesas, ST… pinout&pkg similar to IS31AP4912 but orientation and markings unclear.
- U29 MP1542D ? boost reg
- U30 25L8006E flash
- U31 ‘AUD’* marking, sot563-6 ?, 3v3 buck reg, MP2141N or MP1605
- U32 MP3425? boost reg for 48V
- TR7,8,x : “G4” probably UMG4 dual npn
- DZ5 sot23 “W7B” or “Z8” : zener 9.1V ?
- D32 “76”, rohm RB160MM-60
- D30 “A4” BAV70
- D33: SOT23-6 USB ESD; marking S54 => semtech Rclamp0504S ?
- X? 12MHz xtal
- CN3 a suitable replacement is the USB4105 connector
Measurements, power supply rails #
Note: chassis ground (USB shield, mounting screws) is not directly connected to the digital and analog grounds, and should not be used for probing.
3V3 #
This is always active, and feeds the +1V regulator, EEPROM, clock generator and part of the CPU. In case of a short circuit to 5V, usually only the CPU is damaged.
48V #
The phantom supply is controlled by the cpu.
Parts #
Focusrite have been great at providing parts, in particular the XMOS CPU. This one is crucial because it contains the encrypted bootloader and could not be replaced by a generic part. Unfortunately replacing it is absolutely not a beginner-friendly task, due to the high pin count and thermal pad. The only other custom part would be the EEPROM, all the others should be readily available from normal distributors.