DOM MB Diagnosis page
Board ID:
Rev V5.0L 000471
Source:
From STF testing crew
Symptoms:
Temperature related failures
of Local Coincidence Loopback
tests.
Analyst(s):
G. Przybylski
Analysis Procedure(s):
Operated board in forth monitor
executing lctestboth in a loop. The continuity between TB10 and
T3, or
between JP3-7 and TB10 could be influenced by torquing on TB10 with
tweezers. This implicates trace and via integrity. Removed
keystone solder post, and solder from PTH. Examined under microscope
for cracks in traces. Non faults were positively identified.
August 11; Board fell 3 feet to floor during handling.
Retest:
Install jumper wire from T3-4 to JP3-7 to cure Local Coincidence
loop-back test failure.
No boot failures during about 800 reboot cycles every 2 minutes, while
cycling temperature between -55°C and +65°C every
90 minutes.
With Rev 25 CPLD firmware, this board sometimes fails the boot test.
Low temperature, -45°C to -75°C,
profile - Results:
Many ADC 0 failures at and below -60°C.
ATWD A Ch1 baseline fail at -75°C
Local coincidence loop-back test fails at and below -70°C.
STF @ +65°C produces no failures.
Root cause:
Copper continuity problem.
This is the second case where this net is implicated in an LC failure.
This is the second continuity failure involving the same net... both
problems temperature dependent.
Mitigation:
The most agressive fault isolation
technique would be sectioning the board where the trace meets the via,
in order to allow the examination of the interfaces. So far
this option has not been taken. If additional failures are found,
it may be.
Disposition:
Not for Deployment due to Green Wire Repair.
Use for ATWD tester.
Any Other Information:
Traveler August 7
Traveler August 11
TB10 Via, Oblique view
TB10 Via before flux clean-up.
There is no obvious separation between the via and the trace to the
lower right, but, before removal of the post, the net was intermittent
when torque was applied to the post with a pair of tweezers.
If there is a microcrack, then it is hidden, or filled with solder.
9/13/04 gtp