Mikrokopter Deja Vu all over again

[RTRyder]

As most of you know I recently had the compass board go bad on one of my Hexa, dead, no lights, no power. OK, order a new board and see if the old one can be fixed when I have nothing better to do. New board arrives, I solder the header to the board, install, and go through the calibration routine, nothing, still red light on Navi and Mktool says bad compass error, hmmm...

Tried it a couple times to make sure I wasn't doing something wrong, same result. Went so far as to remove the compass board and install it in the stack of the other Hexa to see if maybe it was something wrong with another board in the first stack, same result, could not get it to calibrate. Great, a DOA board from vendor stock, now I have to RMA the thing and who knows how long this is going to take to get sorted, meanwhile I have no GPS nav on my backup AP craft.

Back when I first built my original Hexa I had the exact same problem and it turned out to be a simple fix once I really dug into it and found the root of the problem so I figured I had nothing to lose trying it again, see if you can spot what's wrong in the picture and remember this is a brand new board from MK...

As it turns out this is EXACTLY the same thing that was wrong with the original board I had over a year ago! What are the odds of that happening? Pretty good apparently and now if I run into this again I'll know right where to start troubleshooting. But Mk never sends out defective boards don't you know, it's always the end user that damages them after receipt, or so they say. Ok, then explain this, not once, but twice and I've got the photographic evidence to prove it...

Here's the first one though the picture isn't nearly as clear as this time around unfortunately...

Ken

P.S. once I fixed the problem it calibrated on the first try...

 

[mbsteed]

How would anyone like myself with an untrained eye ever know that the board was bad? How would I know what to look for in a physical inspection?

 

[ovdt]

RTRyder,

Were the solder joints problematic? I couldn't understand what you did exactly to solve the problem and the problem itself. ( i noticed a weak solder on left side? )

Some lights on this would help newbies like me thanks a lot.

 

[RTRyder]

How would anyone like myself with an untrained eye ever know that the board was bad? How would I know what to look for in a physical inspection?

Exactly! Once you know what to look for the problem is obvious and here's where it is. Look at the picture and find where its labled C21 near the bottom of the right side of the board. Now look directly above it, see the bare copper pad on the small part of the board that comes up through the main board? That pad is the second connection point for the daughter board and what you're seeing is the lack of solder on the pad and just a tiny bit on the pad that its supposed to connect to. It should look like the two connections above it with a nice flowing solder bridge.

It's much easier to see here in the picture which is roughly 2 or 3X the size of the actual board, I needed my reading glasses with a a large magnifying lens in hand to find the problem with a visual inspection. It is the same defect that caused me problems last year on a different board only in that case it was what would be the top pad in this picture that wasn't connected. A person with no electronics experience would probably never see the problem and have to return the board for repair/exchange, fortunately I used to do board repair back in the 1980's so have enough of a background to spot the unsoldered connection as a problem.

Ken

 

[Crash]

Looks like static discharge to me. You should touch some grounded metal before handling the boards. <sarcasm off>

Are y'all still wondering why I bought a binocular microscope? That flaw was easy to see though.

 

[Bartman]

generally speaking, any viewable copper that isn't an unused pad is probably an error, especially when it's on a part where symmetry suggests there should be solder.
if there's some solder but not enough to conceal the copper pad, be suspicious, IMHO.
Bart

 

[mbsteed]

Now that you point out the issue, it seems obvious. Thanks for the education.