[Gta04-owner] GPS fix? Fixed.

Dr. H. Nikolaus Schaller hns at goldelico.com
Sat Nov 26 11:39:04 CET 2011

> Or we use
> a replacement chip that appears to have the switch control signal
> inverted. Christoph just has found one and we are evaluating if
> it is indeed 100% compatible in all other parameters.
> So you don't have to care about this GPS discussion...

Dear all,
we have now replaced the antenna switch chip on three units
and tested them. The internal antenna appears to work much
better with this chip than with crossing over the wires.

So for the coming GTA04A4 boards, we will simply install the
replacement during production.

Now, some of you have an early adopter board (GTA04A3)
where GPS can't work.

My proposal:

* if you want to do it yourself (description below), and can't
easily get the chip, please let me know and I can send you
the chip in a letter envelope.

* or you can send the device to me and we will have it fixed.

* or if you plan to attend the OSHW.de workshop next weekend
in Munich, please bring your GTA04A3 with you. Christoph will
volunteer to replace the chips.



Due to a mistake done when copying the schematics of
the GTA02 to the GTA04 design, the antenna inputs for
the external and internal antennas got crossed over for
the antenna switch chip (uPG2012TB).

Solution: replace the uPG2012TB with a uPG2010TB

The UPG2010TB is slightly different in its parameters, but
has exactly the same pin layout. And - happily - an
inverted truth table. I.e. the same control signal level
throws the switch into the opposite position when compared
to the UPG2012TB.

Replacement: get some uPG2010TB chip
e.g. @DigiKey: http://search.digikey.com/de/de/products/UPG2010TB-A

Remove the uPG2012TB (marked G3A). This requires
SMD removal equipment. A normal soldering iron is
not sufficient! Please be very careful not to damage the
copper pads and traces. And beware that you have to put
a lot of heat into the PCB since it has 8 copper planes
under the chip. This is much more than usual with
single or two-layer PCBs.

Solder the uPG2010TB (marked G2Y) in the correct
orientation. The correct orientation is if you can read
the "G2Y" unrotated and the internal antenna is to the
left, the Wi2Wi GPS receiver on the bottom (marking
in same orientation) and the external MMCX socket to
the right.

Test: you should now see 4-8 satellites within <1 minute
after cold start with external antenna outdoors under
open sky. Unplugging the external antenna and switching
to the internal antenna should still show at least 3-4 satellites.

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