USB Dongle repair.

[JonathanAnon]

Hi lads,

I'm in a bit of trouble. While I was fixing a processor fan issue on a HP desktop PC, I inadvertently broke a USB stick that was stuck in the side of the PC when I turned it over. This USB stick is a dongle for a 3D design program so the guy needs it back working asap.

I took the cover off it and, as I suspected, the 4 pin USB connections had been severed. So I soldered the four pins back on to the little circuit board, then plugged in to the USB to test. Next thing, smoke everywhere, so I plugged it back out again :-( An SMD capacitor evaporated before my eyes. This SMD cap was between the V+ and V- so I assume that it was just a filter cap for the 5v input to the main IC.

http://omg.wthax.org/4EdbCp.jpg

nb. There is nothing on the reverse side of the board.

So I've soldered in a through hole cap 10v cap temporarily as a replacement (you can see the leads on the photo above), but I'm a bit concerned that it might explode again. I checked and double checked and I'm pretty sure that I connected the USB connector the right way (i.e. not upside down), so I'm not sure what happened to blow the cap in the first place.

Any help or advice appreciated

[JonathanAnon]

Re: USB Dongle repair.

Okay small update. I put together a small circuit on a breadboard with a 5v source and a 4.7k ohm resistor. This should set the maximum current to about 1ma.

http://omg.wthax.org/6NbaHS.jpg

I connected the power source to the USB V+ and V- of the usb stick. There was a voltage drop across the resistor obviously so the voltage fed to the V+ and V- was 1.8v. I tested the capacitor and there was 1.8V across it.

So it seems like there is no short on the USB board. But this still leaves me wondering why the original smd capacitor blew ?

[kc8adu]

Re: USB Dongle repair.

mlcc cracked when the board flexed.
then it shorted.
replace and call it good.

[JonathanAnon]

Re: USB Dongle repair.

Yeah that sounds like a more reasonable explanation than I can come up with. I've put it in and it seems to work. Just have to try to locate a good SMD 10V capacitor.

[Kiriakos GR]

Re: USB Dongle repair.

The capacitor is not a critical component, you can skip it.

I would solder on that PCB one 10Cm cable with a connector from a USB extension cable.
And I would use hot glue so to lock everything with it original plastic package.

This is just a key so to unlock the software, it can be plugged in the back USB ports, aesthetics are not an important factor.

[JonathanAnon]

Re: USB Dongle repair.

Just an update:

I was thinking the same way with regard to the usb connector, Kiriakos.. I cut the type A connector from an old phone usb cable, and connected the wires to the USB PCB.. I put the capacitor back on, then I cabled tied the little pcb into a small insulated plastic box. Dropped it back to the guy yesterday afternoon and it seems to be working fine..

PHEWWWWWWW

[Kiriakos GR]

Re: USB Dongle repair.