[evlatests] L302 phase jumps

[Keith Morris]

Vivek:

Do we have any sense of when these symptoms first appeared?  In other 
words, is there evidence that the "phase jumps" predated the last array 
configuration change?



On 8/1/2014 3:55 PM, Vivek Dhawan wrote:
>
> Here is a list of problem units from a test done July 31 evening.
> I'm working to make the test ~10 minutes, we can run it often.
>
> ea11  L302-3,  L302-4.                  ea12  L302-2.
> ea15  L302-3.                           ea22  L302-1,  L302-4.
> ea27  No L302 problems found. But there were delay jumps yesterday.
>        This makes a differential phase jump on an IF pair (deltaA
>        does not equal deltaC).  An LO jump makes identical phase
>        changes on both of a pair.
>
> I am pretty sure after talking to various engineers that this is the
> '128MHz cable adjustment' problem, where the relative timing of the
> 128MHz and 20Hz edges changes with time or temperature. Sometimes it
> is the 20Hz into the L302 which is weak or jittery. Both these things
> should be checked.
>
> I had a thought that it may be triggered by something else, but came
> up empty on 2 counts:
>
> 1. No correlation with L302-x MIB versions (from Hichem.)
>
> 2. L305 modules are being deployed with updated FPGA firmware to change
>     the DTS Timecode from 19.2 to 20 Hz. Below is the list from Leon, I
>     see no correlation with antennas or dates of deployment.
>
>     ea04 - no date recorded.               ea13 - 5/28/2014
>     ea16 - <5/15/2014   ea14 - 6/11/2014   ea06 - 6/19/2014
>     ea10 - 6/19/2014    ea12 - 7/2/2014    ea23 - 7/9/2014
>     ea25 - 7/23/2014    ea05 - 7/10/2014
> ---------------------------------------
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