Kipp&Zonen Brewer MkIII - Manual (Page 16)

MKIII SERVICE MANUAL 11
4 OPERATING TEST FAILURES
In the Brewer Spectrophotometer, most of the operating tests are done using either the mercury
lamp or the quartz-halogen lamp. If any of the other tests fail, the user should proceed immediately
to a mercury lamp test (HG) or a standard lamp test (SL).
Mercury lamp test failures and standard lamp test failures are two major problems which can occur.
In both cases calibration of the instrument may have been compromised. For the purpose of
troubleshooting, these two sections have been separated from the main part of the instrument.
The Light Detection System is made up of the zenith prism, foreoptics, spectrometer, slitmask,
PMT, High Voltage Circuitry, High Speed Amplifier (part of the PMT), interconnecting harnesses,
and the Main Electronics board which houses the photon counting circuits. Without this section
being operational, no testing, or measuring, can be done.
There are a few points to remember in the event there is a major failure somewhere in the system,
whether it is the Mercury Lamp, Standard Lamp, or Light Detection System.
The error message "lamp not on test terminated" is an indication of a failure, either in the
lamps or in the Light Detection System.
Changes in dark count may be symptomatic of a number of problems which may occur in the
Brewer.
If Dark Count begins to increase or becomes erratic, the slitmask may be at fault. Note that it is
normal for Dark Count to increase with temperature.
Dark Count changes may also indicate motor power supply problems, PMT performance problems,
or High Speed Amplifier problems.
If the dark count changes, there may be a changing optical condition in the Light Detection
System. A higher dark count can also be the result of a poor ground somewhere in the system or
high humidity inside the instrument. Grounding connections should be checked, especially between
the PMT housing and the Main Electronics.
The desiccant should be changed more frequently in higher humidity locations.
4.1 MERCURY LAMP CIRCUIT
The Mercury lamp circuitry (Fig 10-4.2) is a constant current source designed to keep the lamp
current constant throughout the temperature range of the instrument. A voltage regulator,
connected to a specially selected resistance wire, regulates the lamp current with minimal circuitry.
4.2 TROUBLE SHOOTING A MERCURY LAMP TEST FAILURE
The Mercury lamp test fails, and software responds with "lamp not on test terminated".
1. Check Motor Positions
Retry the test and look through each Viewing Port to see if the lamp turns on. Ensure that the
zenith prism and the filter wheels are in the correct position.
4 OPERATING TEST FAILURES