DOM MB Diagnosis page
Board ID:
Rev 5.0 SN 0467
Source:
From STF testing crew
Symptoms:
Fails Local Coincidence Loopback
tests
Analyst(s):
G. Przybylski
Analysis Procedure(s):
Test with terminations on both
transformer outputs. Run both LC transmitters with pulse outputs
of both polarities.
Transmit signal into Z1
looks normal, however Receive signal from Z1 looks distorted (instead
of absent)
Recommend removal and testing of Z1, and checking for shorts on
the board. Recommend test of output transformer T1 as well, without
removing it from the board. (I don't suspect T1)
The performance of Z1 was compared with a brand new part. The
output waveforms were significantly different, characterized by spikes
where the rising and falling edges of the pulses should be.
Root cause:
Z1 appeared to have a wire bond
failure on top of one of the pins, where the process of welding may
have pinched off the wire.
A side effect of the removal process was that a resistor pad
delaminated from the board near
the output pins.
After Z1 is replaced, the impedance adjusting resistor can be soldered
between the pins.
See photographs below.
Mitigation:
Effect repairs.
Disposition:
This board can be restored to full
functionality, however, due to the lifted resistor pad, it is no longer
suitable for deployment into the ice. This board will be
used for software testing, or other purposes confined to the northern
hemisphere.
Any Other Information:
