PCB Troubleshooting

mcgyvr

Joined Oct 15, 2009
5,394
Assuming you paid for electrical testing (E-test) or it was included by default with all orders at PCBExpress you shouldn't have any shorts.
I order thousands of circuit boards each year and its very rare (maybe 1 out of 100,000 that make it to me) to have a short but it does happen. That usually means your PCB vendor really isn't Etesting them and its time for a new vendor :) .
An E test will find it.
but 1k isn't a short either really and could easily be from the parts you already soldered.
I can't think of any PCB's I've troubleshooted that ever had a manufacturing defect of anything close to 1k..
Its just a dead short.. Typically just some copper that didn't etch properly or other foreign objects in the base laminate.
.
Damn.. I posted in this thread and of course today I got bit by one of those 1 out of 100,000 scenarios I spoke about...
Dead short between 2 traces (actually from trace to copper pour to the trace on the other side of the pour).
Caused by an etching issue where the copper between 2 traces was not etched all the way leaving 2 small triangular pieces of copper connecting it all together.
It was a dead short and made for some fun "smoke" in my product at the test station :)
Board was "supposedly" E-tested (China source).. A request for corrective/preventative action will be sent to the vendor. (First strike for them since we started using them 2-3 years ago)
 

joeyd999

Joined Jun 6, 2011
6,279
Damn.. I posted in this thread and of course today I got bit by one of those 1 out of 100,000 scenarios I spoke about...
Dead short between 2 traces (actually from trace to copper pour to the trace on the other side of the pour).
This is not all that uncommon. Happens when dust/dirt/fingerprints/scratches gets on the films (if they use film), or imperfection in the photosensitive coating of the pre-process clad.

100% electrical test is an absolute must to guard against it.
 

mcgyvr

Joined Oct 15, 2009
5,394
This is not all that uncommon. Happens when dust/dirt/fingerprints/scratches gets on the films (if they use film), or imperfection in the photosensitive coating of the pre-process clad.

100% electrical test is an absolute must to guard against it.
Yeah like I've said maybe 1 in 100,000 boards make it to us like that.. Even after 100% etest (or supposedly E-tested).. Just ironic IMO that I posted about it and a few days later it happened to me..
 

Thread Starter

dledge

Joined Feb 11, 2014
60
I'm hoping someone is still following this thread...

So, I finally got the board rebuilt. I made a lot of rookie mistakes, but managed to 'correct' the PCB to overcome them. The guidance from this thread was HUGE and enabled me to get the board working...mostly.

I am experiencing a very odd behavior for which I need some guidance. When I connect the board via the two 9V batteries, everything works stellar. When I connect the main power source, everything works as expected UNTIL I attach the motor. Once I do this, the entire board seems to pulse (LEDs, motor, etc.). If I disconnect the motor, and instead connect two LEDs to indicate the motor direction, it again operates just fine. It is almost as if there isnt enough current to operate the motor.

The DC wall adapter is outputting 18V and .83A.

I discovered that I misread the DC adapter and swapped the polarity pins. I've corrected this. What I am wondering, is, would the side pin (which seems to have no connection) be limiting the current?

Any help here would be appreciated. I am at a loss as to what would be causing this.
 

Thread Starter

dledge

Joined Feb 11, 2014
60
Some additional information.

I tried connecting the wall DC power supplier and DC connector directly to the motor. When I did this, the motor exhibits the same pulsing action. I'm guessing I either have fried the Power adapter, or there is some thing about the DC connector that I am missing. Again, any suggestions would be welcome.
 

kubeek

Joined Sep 20, 2005
5,796
Motors usually have about 10x higher starting current than normal running rated current. The power supply is most likely shutting down beacause of overcurrent and then restarting. Try a beefier power supply.
 
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