Nikolaus,
if you need a XRAY machine again, I could probably help you; I work for
a company which produces those XRay inspection machines.
A.
On Sat, 13 Nov 2010, Dr. H. Nikolaus Schaller wrote:
Hi all,
time for another update.
Am 06.11.2010 um 12:35 schrieb Sylvain Paré:
Thanks for the news
Yesterday I received the second board where we
did populate the TPS65950 (power controller).
The results of measurements are:
* the 32 kHz RTC clock is operating
* when inserting a battery, most voltages are
available as expected
Bad news:
* we have a short circuit on the 1V8 rail
I have spent most of the night and this morning to
track this down. It appears to be a solder short circuit
under the TPS chip (a 0.4 mm pitch BGA).
So I am currently sitting at our SMD rework company
and looking over the shoulder of the CTO who has
a lot of experience. Unfortunately I can't make
photos.
We already have unsoldered the TPS chip (that needs
a really sophisticated machine) and the short has
disappeared.
The next step is to solder it back again and do the next tests.
If that works, i.e. we get all voltages from the power controller,
the 26 MHz oscillator should also start working.
If that is ok, the OMAP and the POP memory will be soldered.
Maybe we manage to get it today. Then, we can see if the CPU
is doing something.
Current status: the 1.8V is now working but the VDD2 (1.2 V) not.
The TPS chip aborts the power up sequence early.
We could solve that by adding a jump start resistor.
Rene will upload some photos of the board and we will
post a link.
Here:
http://download.goldelico.com/gta04/images/DSC00671.jpg
http://download.goldelico.com/gta04/images/DSC00672.jpg
Then, we soldered the OMAP3530 and Pop Memory chip and
connected RS232:
http://download.goldelico.com/gta04/images/DSC00679.jpg
It did identify itself as "40W" on the RS232 but did not boot beyond
that. Fortunately the OMAP has a ROM bootloader (which generates
the 40W sequence) and we could use it to download a special
second stage boot-loader that has a simple commandline console
on RS232. Note that it must fit into 64k SRAM built into the OMAP
chip. So we are back to C64 times :)
With this tool, we could identify that the (external) SDRAM has a
stuck-at-1 error on a single bit-line.
So we expected another soldering issue and had the OMAP+Pop
replaced on Monday. But the error pattern remained the same!
Unexpectedly, we were able to put the board into a 3D X-Ray machine
on Tuesday (during Electronica Fair). Here are machine & results:
http://www.yxlon.com/y.Cheetah
http://download.goldelico.com/gta04/images/20111109%20Xray/
Fortunately it is *not* a soldering issue. And likely not a PCB production
issue.
Yesterday late at night we found the problem. It is a bad BGA ball assignment
in our component library. VDDS_MEM (1.8V) is assigned to B17 instead of
B18. And, B17 is data line 14 of the SDRAM and should have been left NC.
Therefore we have tied one data line to a high-level...
I think we can fix that for our samples but it needs some time and we
run out of components for the samples. Especially memory chips have
quite a long lead time. For the series version this will be very easy to fix.
Nikolaus
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