Adjust High Voltage - HP 5890 SERIES II Service Manual

Adjust High Voltage

After the replacement of a photomultiplier tube it may be necessary to adjust the output of the high volt-
age supply to the Photo Multiplier Tube (PMT) in order to attain the optimum sensitivity. After installing
the PMT, the FPD check- out/performance verification must be performed. Results are compared with
those of the original PMT. Assuming gas flow rates are correct, and the system leak- free, the PMT
high voltage should be altered only if there is a significant change in sensitivity. The high voltage is
originally set at the factory for optimum sensitivity; signal/noise ratio (0.90 =/- 0.06 Vdc), correspond-
ing to - 850 V dc =/- 50 V dc at the PMT. The PMT voltage limits are: 0.72 V dc to 1.05 Vdc corre-
sponding to a PMT voltage of - 670 Vdc to - 990 Vdc.
1. Remove the electronics carrier top cover.
2. Remove the right side panel by
removing four screws: two each
along its top and bottom edges.
Noise will appear only about 2/3 as large on analog signal paths than on digital, due to
the high band pass filtering of signal on analog channels.
HAZARDOUS VOLTAGES ARE PRESENT IN THE INSTRUMENT WHEN THE POWER
CORD IS CONNECTED. AVOID A POTENTIALLY DANGEROUS SHOCK HAZARD BY
FOLLOWING ALL REQUIRED SAFETY PROCEDURES WHEN WORKING ON THE
INSTRUMENT.
The following steps require protection against ESD (Electro- Static Discharge).
`
Use a grounded wrist strap (part no. 9300- 0969 - large, or 9300- 0970 - small)
connected to a suitable ground. Failure to heed this caution may result in
damage to the instrument.
When storing or in between handling of PCBs (Printed Circuit Boards), always
`
place them in static control envelopes or enclosures.
3. The FPD detector board is located in the " B"detector board slot. On the board, locate the high
voltage adjustment and the high voltage reference (HV REF) test point (TP7) .
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SCREWS
SCREWS
RIGHT SIDE PANEL
NOTE
SVC 4- 85
ELECTRONICS
CARRIER TOP
COVER