071502 1shift summary

From: Peter Karpius (karpiusp@einstein.unh.edu)
Date: Mon Jul 15 2002 - 17:45:19 EDT


Today's shift was spent troubleshooting the problem PMT's: LTOF11, LTOF13,
and RTOF12. First while the south hall was being opened a run was taken
with cosmics and the raw tube signals were examined. LTOF11 tubes top
and bottom were showing a -50 mV DC offset and a signal measured from
that offset of only -90mV. The current being drawn was a high 1847 uA for
the top and 1989 uA for the bottom - but the HV crate was not tripping.
The raw signals of the other tubes were seemingly normal (i.e. no offset
and with a signal avg. near 400mV). RTOF3top was used as a reference.
 When the hall opened the flasher was turned on and the signals were
checked again. Prior to starting the start counter fiber optic cable was
disconnected both from the splitter box and the start counter. Upon
checking LTOF11 again the DC offset had vanished! Setting the scope
trigger low we saw cosmics at about 350-400mV. A cosmic run was taken and
although the signal for LTOF11 looked fine on the scope, the ADC spectra
was quite distorted, starting at 2000 ch and going off scale.
  In parallel an investigation several hours long was made into the lack
of right ADC's. The delayed analog signal was again checked, this time right
at the input to the ADC and it seemed to fall within the ADC gate. The ADC
left and right TOF cables were swapped and a corresponding electronics map
and root macro were created to reflect this. After taking cosmics runs
the right ADC became visible and the left had vanished. Therefore it seems
that there is a problem (possibly with a slot file?) in reading the right ROC,
or perhaps with that right ADC itself.



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