Latest revision 30 October 1999

          Bad LAD 5 Data on TJD 11459 and 11460

 TJD 11459 = 8 October 1999
 TJD 11460 = 9 October 1999

During several intervals on TJDs 11459 and 11460, the count rates in both
DISCLA and CONTINUOUS data for LA Detector 5 became much too high, most
noticably at the lower energies.  

The spurious high count rates were strongest at the lower energies.
They appeared in all CONTINUOUS data channels, 0-15 (not every channel
was investigated).  They appeared primarily in DISCLA data channels 1 and
2, with only narrow spikes appearing in channel 3.
The reason for the high rates is still unknown.

The incident preceded similar occurrences on TJDs 11462 and 11465 and
followed occurrences on TJDs 11051 and 11119.

In the first interval, completely on TJD 11459, the spurious high rates
began in a data gap and returned to normal after the high voltage was
turned off and on due to SAA passage.  The second interval continued
over the day boundary from TJD 11459 to 11460; the rates returned to
normal by themselves for a short time and became spuriously high and
then back to normal several more times, without the high voltage being
turned off and on.  Later on TJD 11460, the spurious high rates occurred
one more time and returned to normal after the high voltage was turned
off and on due to SAA passage.

From 11460/71358 - 11460/71626, the PMTs for LAD 5 were turned off in
an attempt to restore the LAD 5 rates to normal in case they had not 
already done so.

The approximate time ranges (TJD/SoD) when the spuriously high rates
occurred are
 11459/63179 - 11459/66210 (ended at SAA)
 11459/72176 - 11460/07560
 11460/07720 - 11460/09314
 11460/10811 - 11460/11151
 11460/11798 - 11460/15048
 11460/57644 - 11460/58699 (ended at SAA)

Quality Flags 75 (indicating high count rates in LAD 5) were set for
the following TJD/SoD intervals:
 11459/63000 - 11459/67000 (during SAA)
 11459/72170 - 11459/72250 (not sure why this was separated from next)
 11459/72300 - 11459/86399
 11460/00000 - 11460/07560
 11460/07520 - 11460/09314 (mistake: should have started at 07720)
 11460/10809 - 11460/11153
 11460/11796 - 11460/15048
 11460/57642 - 11460/58800 (during SAA)
 11460/71330 - 11460/71660 (when commands were send to turn off and on
                            each PMT for LAD 5)

No triggers occurred during the time intervals with the spurious rates.