Kipp&Zonen Brewer MkIII - Manual (Page 21)

MKIII SERVICE MANUAL 16
5. Test Slitmask
Slitmask operation can be confirmed by returning to Telytype operation (TT), sending the R,0,7,20
command, and noting that the slitmask moves back and forth pausing briefly at each of the 8
slitmask positions.
Commands R,X,X,20 (where X =0 to 7) can be sent in sequence. After each command a slot in the
slit mask should line up with a slot in the slit plate EXCEPT on command R,1,1,20, which is the
Dark Count position. If the slitmask does not move, or appears to move incorrectly, then the I/O
cable, Motor, or the motor control micro or motor driver IC on the Main Electronics board may be
faulty. The Main Electronics board should be replaced and another test attempted.
6.Check Dark Count
If the slitmask appears to be functioning correctly note what the count values are when the
command R,0,7,20;O is issued in Teletype. There is a very important difference between a count
rate of zero and a count rate near zero. A high count rate indicates correct operation. A low count
rate indicates that only dark count (a function of the PMT) is being measured and the light coming
through the slit mask is not being measured. A zero count rate indicates a problem with the PMT
or its electronics.
7. Measure High Voltage Test Point
Replace the Spectrometer cover, and remove the cover from the Main Electronics board.
Measure the high voltage test point E16 on the main electronics board (see picture), if it is not the
same as the value given in the Final Test Record, section 5.0, then adjust R4 on the high voltage
control board.
8. Check High Voltage Cable
If the test point voltage cannot be achieved, there may be a short circuit in the high voltage line
somewhere between the HV module and the actual PMT dynode chain. Care should be taken
when inspecting this area because there can be as much as 1800 volts at the connection points.
Check the high voltage cable for continuity.
9. Measure High Voltage at PMT
The rear cover of the PMT housing can be removed (turn CCW) and the actual high voltage
measured on the internal connector. This measurement must be done with a voltmeter rated for
2000 volts or by using a high voltage probe.
If the high voltage is still not as indicated on the Final Test Records, then contact KIPP & ZONEN.
10. Test High Speed Amp Board
If high voltage is correct, there may be a failure in the high speed amp board. TP1 on the high
speed amplifier board (inside the PMT housing) should read -10 millivolts (referenced to the HV
connector shield) or the value recorded in the Final Test Record, section 4.0. If the value of this
test point is incorrect, an adjustment of the on-board potentiometer can be attempted. If this test
fails, replace the high speed amplifier board.
If this test point is normal, the photon counter cable should be inspected to ensure that all
connections and wires are in tact. Finally, an oscilloscope can be used to monitor test point TP4 on
the high speed amp board, and then pins 1,2,3,4, and 12,13,14, 15 of the IC, SN75114N. There
should be clean square waves, the frequency of which should vary with light intensity.