Focusrite Scarlett Audio Interface Repair - Customer plugged in 24v instead of 12v.

⭕ We are an Amtech Flux Distributor. Buy AMTECH NC-559-V2-TF Flux

UNI-T UTi260B thermal Camera

Grinding pen

Low Melt Solder

NorthridgeFix T-shirts

=================================================== If you are local, drop in and say hello
NorthridgeFix
19365 Business Center Drive, Unit 7
Northridge, CA 91324

Phone: [phone]

[lukaswalczak]

This component is called a common mode choke in a 2020 package i guess. It is an inductor for filtering high frequency signals out of the switch mode power supply, that could interfere with the rest of the device. For a 12V input you generally look for a mOhms rating, (4-10mOhms) and a high DC current (i.e. 3-4 Amps). For the impedance, 100-200 Ohms at 10-50 MHz would work perfectly. An example would be: PLT5BPH1015R6SNL (Mouser). The values are not too critical, so a variety of components could be used as a replacement.

[ptkashinathmishra]

That coil looks like common mode choke for power filtering, can be shorted or replaced with any filter. It basically stops HF from powerline, also that removed C333 cap could be 1nF or 10nF on power line. This is my experience with audio circuits.

[stilus]

Hello, Alex!
C333 = 100nF 50V capacitor
L21 = choke common DLW5BTN142
D34 = RB160M-30

Have a nice day! :)

[crnlbwlawson]

I love all the helpful comments below. We electronic engineers got to stick together. (Not the scientist 😉) Alex, the man sent you chocolate!! We got to get him back up and running! I appreciate all your hard work, and willingness to share!

[ayan.debnath]

I am really excited too see so many comments to help fix this board!
Thats the power of community.

[karlfell]

The blown diode after the choke coil is likely to be a TVS diode, probably around 18v to protect from overvoltage conditions. Once triggered it will clamp the input line to a short which is why the coil got cooked. You can completely remove the diode and bridge accross the coil contacts and should work normally. Karl

[devonwilson]

Greetings. Thanks Alex for sharing. This video is exceptionally educational. There is value in you sharing not only how you isolated the defective inductor but also providing the reason why it is defective by showing the measurements. For sure, if they are to be isolated, the windings should not be shorting from winding to winding. Thanks to all the individuals providing the great comments as well.

[kevina.]

That magnetic component (L21) is likely a common mode choke. Based on its proximity to the power input, it is probably intended to reject AC noise that could be coming into the DC input if you had a noisy 12 volt AC-DC wall wart with poor common mode rejection.

You could jump it and the device should continue to work. However, being a hifi audio digitizer, the absence of that cmc could allow line noise in under certain conditions. I would do a parametric search on digikey/mouser for a surface mount common mode choke and see if any pictures match the part.

[fichambawelby]

Alex: you can freely remove the double inductor, because it is acting as a supressor. Not a switching PSU nor any other thing. Take into account that you are working with a digital audio interface, and they want always the cleanest possible input voltage. But you are free to put a couple of jumpers instead of the double inductor. The diode must be changed. Maybe it is a Schottky diode, very fast one. It is there to avoid reverse polarities, and even over voltages. Change diode, jump inductor pads, look for short in the small ceramic cap, and if it's OK, you are done.

[kalarMin]

The inductor together with the capacitor and the diode is the input filter for the surges and the electrical noise of the power supply. Bridge the opposite sides to allow 12v to pass through the circuit. Your customer may need a very good quality power supply.

[DLSDKING]

Thats a power line filter. It composes of two inductors in one package where in the coils are wound over a same core. Because of high current through the coil, the insulation melted and fused coils. You can use shunts temporarily to power and test the device.

The diode in that configuration looks like a reverse polarity protection(The reverse brekdown voltage might have exceeded) or it may be a Transient voltage suppresor(shorts high frequency pulses). You can omit it temporarily.

The reason why the short was not detected with your current approach is because unlike a digital logic circuitry, in analog system design there are multiple grounds isoloated. The ground of digital logic is isolated from analog logic and the ground of powersupply is for sure not connected ground in analog design(In typical audio amplifiers, we use something called virtual ground built with resistor dividers buffered by an rail to rail op amp. This is done to balance the voltage rails for amplifiers and reduce power line noise). There may also be isolated power supplies but cant say coz we didnt get to see whole board layout.

[robertpage]

I looked on line and found that the model you have is the Focusrite Scarlett 1 8i8 a second generation model.
I cannot find a full board schematic.
The company is British.
I sent them an email and described the model of the unit and the board location of the part (inductor L21) and asked them for the info on it (Maker and part number and value.
I'll get back to you as soon as I hear from them.

[OnStageLighting]

I discovered a while back that the pointed end of a plastic spudger makes a great marking tool when prodded onto something at 100 degrees C. Follow the black melted plastic....

[Mladjasmilic]

Electrical engineer here.
You have 2 inductors on same core in order for AC components from power supply to cancel each other. This is typical filter with capacitor - inductor - capacitor. But it is only useful when old school power supply with transformer is used, in order for it not to pass audible mans frequency. Modern SMPS use very high frequency, and you can not hear them anyway. It can slow down the charge of second capacitor, to not over current it. Can be bridged.
As for broken diode - it is used to not have backflow of current on liner power supply (they had huge ripple), again for audible noise suppression. Again, you could bridge it over or put any other SMD diode rated for the current (5A should be enough). I think that it got fried while trying to charge the big capacitor after it. While cap is not short, I would replace it too, as it experienced over voltage and over current and may be destroyed internally.
I am suppressed that this device has no fuse. So I would put one in place of gone inductor. Input capacitor is not needed, but if you put one back, it should be low capacity and rated at least 16v.

To sum up:
Input SMD capacitor: Not needed. Can be replaced with any 16V low value capacitor.
Inductor: Not needed, can be bridged.
I recommend to put fuse on positive and inductor on negative side.
Secondary cap: Replace with 16V one with similar capacity.
Diode: Replace with 5A one. Can be bridged.
Big cap after that: Replace with similar.

[Bi]

RIP last comment was deleted I guess cause of a link. But you can contact focusrite for either the spec of the component or a replacement component. I've repaired 4 of them now and each of them they shipped me the components I needed free of charge. That system looks like a scarlet 18i8 2nd gen. The first gen had a black usb port, 2nd had the white usb port and 3rd+ was a complete revamp of the systems and they moved to usb c.

[MUAW_IO]

It's a common mode noise filter which is two coils magnetically coupled on the same core. It's used to to prevent noise coming into (or leaving) the device, for test purposes you can jumper it out but it may cause problems with audible interference if you send it out like that or with two separate inductors, the whole idea of a CM choke is that the two sides are magnetically coupled.

You should be able to guesstimate a suitable replacement from the dimensions and the expected current draw of the interface.

[jonsnell]

I would say, having repaired many of this type of device, the adaptor was the wrong polarity, that cooked the diode sat across the supply. After a while the common mode choke that has a sole function of removing interference, shorted out due to the overload.
Cheap enough to replace and available through Mouser, RS Components and many more wholesalers.

[jamesbrown]

DZ3 should be to protect against overvoltage, so I'd check that component next; it's possibly shorted out (if not, do your usual method for finding shorts).

Looks like C333 is across power in, and probably 10n or 100n (probably same value as C321). The "inductor" will be a common-mode choke, and value will not be critical either. These parts are for noise suppression of the input power supply. D34 will be a polarity protection diode.

[ThriftyToolShed]

I can hear the current hum on the audio channel as soon as you turn it on.

[rebus]

I have in the past searched the patent number on the device & obtained description of operation & a schematic from patent, it was for a RV power supply that was 110v & was plugged into 220v, was able to repair & still using it 10 yrs later, it's one of the new switchers.