mini USB breakout board burned? - Page 1
Forum section: electronics / repair

author: Electro Fan
author_rank: Super Contributor
timestamp: January 17, 2015, 04:15:47 am
content: Hi, I ordered a mini USB breakout board and carefully (I thought) soldered a 5 pin header to the board (VCC, D-, D+, ID, GND).To test it I hooked it to a PC USB port with a USB to mini USB cable and checked it with a scope (probe to VCC and probe ground to GND). My scope showed 5 volts as expected but within a minute or so I smelled something burning and saw a bit of smoke coming from the board. I can see that the board trace from the USB connector to the VCC pin is burned.I'm presuming that simply probing the board shouldn't cause it to heat up and burn, right? So maybe I damaged the board when soldering the header, or maybe the board was defective? What do you think?Thanks, EF

author: sleemanj
author_rank: Super Contributor
timestamp: January 17, 2015, 04:41:38 am
content: Quote from: Electro Fan on January 17, 2015, 04:15:47 amI think we need to see a photo.You did check for shorts in your soldering job before hooking it up to your computer... right?

author: aargee
author_rank: Frequent Contributor
timestamp: January 17, 2015, 07:08:35 am
content: Disconnect your probe from the circuit and use a multimeter to measure AC and DC voltage, then try AC and DC current between USB ground and ground on the Oscilloscope while the PC is on, especially if it is a laptop

author: Electro Fan
author_rank: Super Contributor
timestamp: January 17, 2015, 05:07:24 pm
content: Quote from: sleemanj on January 17, 2015, 04:41:38 amThanks. Uh, no...What technique would you use to check for shorts for this board? Thanks

author: Electro Fan
author_rank: Super Contributor
timestamp: January 17, 2015, 05:18:59 pm
content: Quote from: aargee on January 17, 2015, 07:08:35 amThanks - I did check the board with a DMM while it was attached to the PC but I only checked for DC; I found it to be 5V. Why would it be good to check for AC? Also, why would you check for AC and DC current between the USB ground and the ground the scope? Are these tests to check to see if somehow the USB connector on the board was mis-wired? What steps would you take to run these tests? Thanks again

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 17, 2015, 05:30:47 pm
content: The only thing I can think of is that you somehow connected the scope ground to the VCC.

author: Unknown
author_rank: Unknown
timestamp: January 17, 2015, 05:51:01 pm
content: From the photos you posted is impossible to see the solder joints of the usb connector.When you solder these mini b connector is very easy to short the pins to the back of the case.Did you measured the resistance beetwen vdd and ground with a DMM before plugging the board ?

author: Electro Fan
author_rank: Super Contributor
timestamp: January 17, 2015, 11:25:07 pm
content: Just to clarify, the mini usb connector came installed on the board; I just soldered the header pins to what were 5 holes on the board

author: Electro Fan
author_rank: Super Contributor
timestamp: January 17, 2015, 11:28:28 pm
content: Quote from: PA0PBZ on January 17, 2015, 05:30:47 pmNot super likely but possible....

author: Electro Fan
author_rank: Super Contributor
timestamp: January 17, 2015, 11:30:25 pm
content: Quote from: exapod on January 17, 2015, 05:51:01 pmNot before I plugged the board; currently (with the burned trace) vdd to ground resistance is 0.F on the DMM

author: Skimask
author_rank: Super Contributor
timestamp: January 17, 2015, 11:34:52 pm
content: Quote from: Electro Fan on January 17, 2015, 11:30:25 pmHow about on the USB connector side of things? (not the header Vdd to ground, but pin 1 on the usb connector to ground)

author: Electro Fan
author_rank: Super Contributor
timestamp: January 18, 2015, 04:35:39 am
content: Quote from: Skimask on January 17, 2015, 11:34:52 pmThanks for the idea - I would never have thought of testing on the USB connector leads - they are very small and hard to see. Turns out I was able to get the DMM probes on the small contact points - it still reads 0.F. What should it read if it is working properly? Thx

author: sleemanj
author_rank: Super Contributor
timestamp: January 18, 2015, 07:33:38 am
content: What did you have connected to the header that you soldered on?Clearly a lot of current has passed down that VCC trace.My best guess is you accidentally connected your scope's ground clip to the VCC header, completing a circuit from your computer's +5v, down that VCC trace, into scope's ground, into the mains ground, and back into the computer's power supply to the negative, and promptly the trace fused due to over current.

author: Electro Fan
author_rank: Super Contributor
timestamp: January 18, 2015, 08:47:28 am
content: Quote from: sleemanj on January 18, 2015, 07:33:38 amI used some short female to male breadboard connector wires (you can see them partially in the top two photos) to extend the VCC and GND pins from the header so I could connect the scope probe and probe ground without touching any of the other 3 header pins. Despite this effort to make good connections it seems like the consensus is that I somehow reversed the VCC and GND connections to the scope probe and scope ground. I am going to assume that is what happened whether it did or didn't and look more carefully at connections going forward - so it's a lesson learned. Thanks for the help.- But just to confirm, had everything been working normally and I put the scope probe on the board VCC and the probe ground on the board GND the scope should have simply registered 5 Volts and everything should have worked fine no matter how long the board was connected to the PC USB port, right?

author: sleemanj
author_rank: Super Contributor
timestamp: January 18, 2015, 08:55:12 am
content: Quote from: Electro Fan on January 18, 2015, 08:47:28 amYes, that's the theory.

author: Electro Fan
author_rank: Super Contributor
timestamp: January 18, 2015, 06:07:23 pm
content: Ok, Thanks for the help.Round two: I happened to have another similar (USB to 5V or 3.3V selectable) board on hand. I tested the GND to 5V and GND to 3.3V pin connections for resistance before plugging anything in and got values in the several hundred thousand ohm range. So I proceeded to connect the board to a USB port on another PC (with less valuable data) and probed it (after carefully checking the connections) with a DMM. A little over 5V and 3.3V as expected. Then I moved to the original PC (feeling bold) and probed with the DMM and then scope. All good!Moral of the story, pay attention when connecting stuff

author: sunnyhighway
author_rank: Frequent Contributor
timestamp: January 19, 2015, 08:29:42 pm
content: Quote from: Electro Fan on January 18, 2015, 08:47:28 amThat scope you are talking about, does that scope happen to be one of those USB dongle scopes you have to use with a pc and some software?

author: Electro Fan
author_rank: Super Contributor
timestamp: January 20, 2015, 04:25:57 am
content: Quote from: sunnyhighway on January 19, 2015, 08:29:42 pmThe scope is a Rigol 2072