[time-nuts] Teardown of Chinese made eBay GPS antenna.

John Green wpxs472 at gmail.com
Thu Feb 22 14:48:24 EST 2018

For those who have been following the saga of the Chinese made, eBay
purchased antenna that failed, I may have an answer as to why it failed.
I had to destructively disassemble it. I just could not get it apart any
other way. I used a Chinese version of a Dremel tool with a metal saw
blade. After making a huge mess with plastic particles everywhere, it
revealed a circular FR4 board with two patch antennas mounted, one atop the
other. I assume the smaller one to be the L1, and the larger to be L2. This
part looks almost identical to the Trimble Microcentered antenna I worked
on recently. On the back side of this is a metal shield  about 3 by 3
inches soldered to the circular FR4 board. I switched to a abrasive wheel
and took off some of the solder holding the shield to the board. Then,
using a small screw driver, I went around the shield breaking the solder
loose. The shield off revealed that the coax goes to some capacitors that
couple RF out and through an inductor with some capacitors to ground and
finally to a SOT23-5 package labelled LK33. This appears to be a Micrel
MIC5203 3.3 volt regulator. It is shorted on the input side. I believe that
putting anything over 7.5 volts on the input exceeded the power dissipation
rating and caused it to fail. I plan on wiring up a more robust 3.3 volt
regulator in its place and trying again. It looks like I will be able to re
solder the shield back. The watertight integrity is gone for good. I think
I can find a plastic box I can mount it in so I can at least experiment
with it. I have sent a message to the seller detailing my findings. The
Micrel part lists a 20 volt maximum input voltage, so in theory at least,
this might have worked, and there might be some of these out there that
don't fail.

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