Author Topic: Need to figure out this missing SMD chip  (Read 150 times)

0 Members and 1 Guest are viewing this topic.

Offline gotofbi

  • Contributor
  • Posts: 19
Need to figure out this missing SMD chip
« on: April 02, 2020, 10:39:26 am »
Hi,

I am trying to repair car diagnostic dongle.
My friend kicked usb cable and it removed USB-B connector.

I cleaned old USB connector and was prepping to install new connector.

However, I noticed that it is missing one of SMD connector right beside of USB connector.
I touched that area with soldering iron while I was removing USB connector and not sure if the wasn't there from beginning or got removed by accident.

I googled if I can find picture of the board and I only found one with lower resolution.
To me, it looks like I am missing some SMD part but not sure what it is.


Here is the finding that I have
1. Black boxes are connected to GROUND
2. Red box is the one that Im missing
3. Blue box seems to be same one that supposed to be on Red according to low resolution picture
4. Tested Ohm value of Blue box and it shows 0 ohm which I think its not Capacitor (correct me if Im wrong)
5. Both pads on Red box are connected to ground


So, am I missing a SMD component? or it wasnt there from beginning?
If Im missing something, what could be there?


Thanks,

High res image of working area
961684-0

Low res of image where I found online. (to my eyes, there is a component thats missing on my board)
961688-1
« Last Edit: April 02, 2020, 10:42:12 am by gotofbi »
 

Offline blueskull

  • Supporter
  • ****
  • Posts: 13271
  • Country: cn
  • Power Electronics Guy
Re: Need to figure out this missing SMD chip
« Reply #1 on: April 02, 2020, 10:46:35 am »
That part should be left missing. The part bridges between system ground and USB shield.
Normally, you are supposed to commect system ground and USB shield with an RLC network to shunt RF noise and to block 50Hz/60Hz ground loop noise.
There is a risk of increasing EMI noise, though, so when people design PCBs, they tend to leave a shorter link across USB shield and system ground, just in case they didn't pass EMI test.
If it passes the EMI test, they will keep the design. If not, they will short the link and live with ground loop noise in favor of lower EMI.
 
The following users thanked this post: gotofbi

Offline gotofbi

  • Contributor
  • Posts: 19
Re: Need to figure out this missing SMD chip
« Reply #2 on: April 02, 2020, 10:56:49 am »
That part should be left missing. The part bridges between system ground and USB shield.
Normally, you are supposed to commect system ground and USB shield with an RLC network to shunt RF noise and to block 50Hz/60Hz ground loop noise.
There is a risk of increasing EMI noise, though, so when people design PCBs, they tend to leave a shorter link across USB shield and system ground, just in case they didn't pass EMI test.
If it passes the EMI test, they will keep the design. If not, they will short the link and live with ground loop noise in favor of lower EMI.

Thank you so much,
I will proceed to solder new USB connector!
 

Offline blueskull

  • Supporter
  • ****
  • Posts: 13271
  • Country: cn
  • Power Electronics Guy
Re: Need to figure out this missing SMD chip
« Reply #3 on: April 02, 2020, 11:01:54 am »
On a second thought, the part is NOT from USB shield to GND. It is across the cap, which is then series connected to the GND. You may want to put a 1k resistor there, but it won't change much.

The entire section over there can be either shorted, all removed or left as is. They will not affect the functionality of the circuit at all. It's all about ground loop noise, ground loop voltage retention and EMI.

Those are the bullshit you need to focus if you want to legally sell a thing. Not something that has anything to do with functionality.
 
The following users thanked this post: gotofbi

Offline gotofbi

  • Contributor
  • Posts: 19
Re: Need to figure out this missing SMD chip
« Reply #4 on: April 02, 2020, 11:44:15 am »
On a second thought, the part is NOT from USB shield to GND. It is across the cap, which is then series connected to the GND. You may want to put a 1k resistor there, but it won't change much.

The entire section over there can be either shorted, all removed or left as is. They will not affect the functionality of the circuit at all. It's all about ground loop noise, ground loop voltage retention and EMI.

Those are the bullshit you need to focus if you want to legally sell a thing. Not something that has anything to do with functionality.

All my intention was to fix the unit.
Its not my design nor I have capability to create duplicate one.
Anyway, I soldered new USB connector with leaving Red box as is

IT WORKS!!!

Thank you so much!!
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf