Author Topic: Repair Usb Audio interface Focustrite 2i4  (Read 5227 times)

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Offline magic

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #25 on: January 20, 2020, 10:10:59 am »
USB 1.x/2.0 devices should tolerate shorts between any two pins indefinitely.
That being said, maybe that's too much to expect from audio gear :-DD

Post a pic of the blown parts and their neighborhood.
 

Offline Countrypicker

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #26 on: January 20, 2020, 12:35:12 pm »
Hey Magic,  thanks for the fast reply. I'm at work right now but I will take pics when I get home (Based in Scotland). I just figured out what those codes are (SMD Codes). I'll use a big magnifier and see if I can decipher the code. I used to be an electronics tech way back in my Air Force days but they didn't use surface mount components in those days. (Old Timer)  ;D. Regarding shorting out pins, I wonder what 5 volts down the input pins of the USB Controller chip would do. It already blew off the little inductors at the input. Also blew off chip U38 and R51. I have ordered a USB3343 chip just in case.
 

Offline Countrypicker

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #27 on: January 21, 2020, 11:53:53 am »
Pics attached. I found U38 detached inside the casing. It is marked SDERCG. A previous comment says this is NCP303LSN09 but I think that's wrong. I looked up the SDM code and it says LM3670MF-3.3. That's a DC Voltage drop down device 5 Volts to 3.3. Makes sense as the Processor, USB Controller and the Cirrus Logic DAC all use 3.3 volts. U39 is marked Z074. That appears to be  a Fairchild NC7WZ07P6X Dual Buffer. The middle 2 pins appear to be unconnected so that ties in with the Chip schematic. C137 should be 1 uF capacitor according to USN 3343 Data Sheet.
 

Offline Zucca

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #28 on: January 21, 2020, 12:30:14 pm »
I found U38 detached inside the casing

Strange, those do not came off so easy, do not spit on my face but maybe is overheating and desoldering itself?
It's a mistery.
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Can't love what you don't know. Zucca
 

Offline Countrypicker

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #29 on: January 21, 2020, 12:56:55 pm »
R51, L5, C137, C139 all missing. C137 should be 1 uF according to the USB3343 Data Sheet. Not sure about C139 - maybe it was never there. This was caused by someone trying to replace the USB connector. He shorted the Data pins to the +5V line with a solder splash.  :palm:
 

Offline Zucca

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #30 on: January 21, 2020, 01:07:19 pm »
Another moron before us, very common story unfortunately.
Can't know what you don't love. St. Augustine
Can't love what you don't know. Zucca
 

Offline magic

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #31 on: January 21, 2020, 02:10:36 pm »
Regarding shorting out pins, I wonder what 5 volts down the input pins of the USB Controller chip would do.
Nothing interesting in principle, though I haven't had an opportunity to test it in real life yet :)

Universal Serial Bus Specification Revision 2.0, 7.1.1 USB Driver Characteristics, page 124
Quote
A USB transceiver is required to withstand a continuous short circuit of D+ and/or D- to VBUS, GND, other data
line, or the cable shield at the connector, for a minimum of 24 hours without degradation.  It is recommended
that transceivers be designed so as to withstand such short circuits indefinitely.  The device must not be damaged
under this short circuit condition when transmitting 50% of the time and receiving 50% of the time (in all
supported speeds).  The transmit phase consists of a symmetrical signal that toggles between drive high and
drive low.  This requirement must be met for max value of VBUS (5.25 V).

I will tell you what happened: the previous owner knocked these components off the board while trying to replace the USB connector. Or maybe desoldered them and couldn't put them back. Or lost them, or broke them during desoldering.

Either that or he managed to apply mains voltage to the USB input. But there are no smoke stains.

As for the data lines, I bet they go straight through L5 to U4. L5 was a common mode choke to suppress EMI, the device will work without it (replace with two straight wires). Then you may look for a proper replacement, but I am not familiar with that stuff.

The only serious problem is the mayhem around U38. You need to identify it. It doesn't look like a switching regulator, because there is no coil in the vicinity.

edit
Trace how things are connected around U38 and U39 and post a schematic.

That guy from Poland has 47kΩ at R51. Both he and the Brazilian have nothing at C139.

Is your U38 visibly broken or only disconnected from the board?
« Last Edit: January 21, 2020, 02:34:11 pm by magic »
 

Offline Countrypicker

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #32 on: January 21, 2020, 04:51:17 pm »
I see from other pictures on the web that C139 is empty so can rule that out. Yes, the data lines do go through L5 to pins 13 and 14 on the USB3343. I have a replacement choke for L5. I am fairly sure I have correctly identified U38. (LM3670MF-3.3) The part I found rattling around inside the device has no connections to solder it back in. Just a black chip with no legs and marked SDERCG.
 

Offline magic

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #33 on: January 21, 2020, 09:50:07 pm »
I wonder if this thread might be about the same one unit which is being broken a little bit more by each new owner and then sold on eBay to the next one :P

U38 is not LM3670-3.3, don't try it. Firstly, the marking doesn't match (SDER vs SDEB). Secondly, there is no inductor nearby so U38 wasn't an SMPS chip.

Too bad that the original part is nonfunctional. NCP303LSN09 is a reasonable match (the datasheet says: marking SDE). You may order a new one and see if it looks the same (same number of letters, font style and size).

Try to figure out how the circuit is wired and whether NCP303LSN09 makes sense in this place in terms of pinout and function.
 

Offline Countrypicker

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Re: Repair Usb Audio interface Focustrite 2i4
« Reply #34 on: January 22, 2020, 11:05:37 am »
Thanks Magic. NCP303LSN09T1 ordered.
 


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