Focusrite Scarlett 2i2

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Focusrite Scarlett 2i2 is a USB digital audio interface. It has two combined 1/4"(6.3mm) Jack and XLR analog inputs which support both line level and microphone level inputs. The interface is equipped with phantom power that can be turned on or off for both of the inputs at once. It has two mono 1/4"(6.3mm) Jack analog outputs and one stereo 1/4"(6.3mm) Jack analog output that can be used for direct monitoring of the analog inputs.

The first generation's digital interface supports sample rates of up to 96 kHz at up to 24 bits per sample. Its later generations (the 2nd and 3rd as of 2021) support sample rates of up to 192 kHz at up to 24 bits per sample.

Focusrite Scarlett 2i2 first generation[edit | edit source]

Problem Solution

Device is not turning on. The USB LED intermittently lights up. The main +5V, -5V and 3.3V power rails are low or are intermittently raising and lowering in their voltage to ground.

One or more of the 4066 chips on the board have probably failed. Replace them.

At first, disassemble the device and expose the board. Then check the voltages to ground (e.g. the metal casing of the USB port) at the following control points:

  1. TP1 3V3 test point - the voltage should be 3.3V - this is the main 3.3V power rail
  2. outer side of C19 capacitor - the voltage should be +5V - this is the main +5V power rail
  3. outer side of C17 capacitor - the voltage should be -5V - this is the main -5V power rail

The C19 and C17 capacitors are located next to each other. The "outer" side referred to in the above paragraph refers to the side that is further from the other one.

If the voltage to ground on +/-5V power rails is ~ +/-0.5V, then it is likely that one or more of the device's 4066 chips (I am not fully sure of the exact part number, probably these: MC74HC4066A with package type SOIC-14 and case outline 751A-03) have failed. These chips are located at the positions U24, U25 and U26. They are inexpensive (~0.5 USD per chip) and can be bought from Mouser or Digi-Key. Before buying a specific chip, it is reasonable to consult with Focusrite support about the exact chip needed for your particular device.

During this specific failure, it is possible that the 3.3V power rail will remain mostly working. It is also possible that the R127 resistor will be heating up excessively. In such case, it is better to not keep the board powered on for too long so that the risk of further damaging the other components is minimized.

R127 resistor which may get very hot

Replacing these chips is simple with a hot air rework station, flux, soldering iron and solder. It is perhaps possible to do so also with a pair of hot tweezers that have sufficiently large tips but I did not try it.

In my case, the 4066 chip which has failed was the one at the position U26. I have determined it by measuring the continuity between its pins when desoldered and finding out that roughly half of them are shorted together. This is not the case with a fully working chip. Anyway, to be sure, I have replaced all three 4066 chips.

The 4066 chip at the position U26 after replacement

When replacing the chips, especially with hot air, it is reasonable to take extra care to not misplace the other components on the board like the small resistors or capacitors. In addition, it is necessary to be careful with cleaning up the pads because they can easily be ripped out from the board. Also, it is advisable to orient the air in a way which would not heat the white caulking material that seals the ends of a ribbon cable which connects the two boards together. If it gets heated up too much, it may melt and start to float, covering some neighboring components as a result. It should not be a problem to have some components covered by it but further work on such a board may become difficult.