HEWLETT PACKARD (HP) 6188
Service Manual

Sect. N Page 22 11) Set the PULSE RATE control to 40 pps, with the other controls remaining unchanged. Set oscillator to 40 cps. 12) Adjust R117 so that the generated pulse rate is 40 pps. 13) Set the SYNC SELECTOR to X10 and check the calibration o the PULSE RATE dial in vicinity f o 40. R117 can be readjusted to improve calif bration accuracy if desired. 14) Refine the above adjustments as desired or for best overall accuracy.

Model 618B 1) Connect the RF OUTPUT through a crystal detector to the vertical input of an oscilloscope having an accurately calibrated sweep. 2) Connect the SYNC OUT connector to the SYNC connector on the oscilloscope.

3) Set the PULSE WIM'H control to 10 microseconds.
4) Adjust R156, Figure 4-6B and 4-13, so that the width of the generated pulse is 10microseconds as measured on the oscilloscope.

5) Set the PULSE WIDTH control to 1microsecond.
4-18
C A L I B R A T I N G THE PULSE DELAY D I A L

Replacing V107 may lessen the accuracy of the PULSE DELAY dial. After replacing V107,' the following procedure can be used to adjust thedelay calibration; however, the calibration of the PULSE DELAY dial is intended only to be approximate. 1) Connect the DELAYED SYNC OUT terminal to the vertical input of a n oscilloscope having a n accurately calibrated sweep.
2) Synchronize the oscilloscope from the SYNC OUT connector.

6) If necessary, s l i p dial to read 1microsecond. 7) Repeat steps 3, 4, 5 and calibration accuracy.

6 f o r best overall

of rf pulse will vary approxi8 ) The width the mately 1/4 microsecond as the generator is tuned through its r range. The above adjustments can f be made f o r best accuracy at any desired rf
frequency.

3) Set PULSE DELAY control to 300 microseconds. 4) Adjust R133, Figure 4-6B or Figure 4-13, to give a delay of 300 microseconds as measured on the calibrated oscilloscope screen. ' 5) Set PULSE DELAY control to 3 microseconds as read on oscilloscope screen. If necessary, slip the PULSE DELAY dial on its shaft to make calibration accurate. The delay is indicated by the interval between the start of the oscilloscope trace and the leading edge of the DELAYED SYNC OUT pulse. 6) Repeat steps 3 and 4 for best overall calibration.

4-20

LUBRICATION

It is not expected that the mechanical parts of the signal generator will require lubrication within the first year of operation. Moving parts such as the attenuator and power monitor rack g e a r s are lubricated at the factory with Lubriplate 105V, Fiske Brothers Refining Co., Newark, N. J. The frequency drive g e a r s behind the front panel are lubricated with a mixture of Shell Tonna Oil G and Molykote Type M. The drive mechanism shown in Figure 4-11 is lubricated with ShellTonna Oil G. ' Do not lubricate cavity plunger rods.

4-21

REPLACING REFLECTOR POTENTIOMETER R 1 7 4

4-19

CALIBRATING THE PULSE W I D T H DIAL

To replace potentiometer R174 on the frequency drive casting, refer to Figure 4-14 and proceed as follows:
1) Disconnect blower tube at cavity.

Replacing V l l l may lessen the accuracy o the f PULSE WIDTH dial. After replacing the V111, the following procedure can be used to calibrate the PULSE WIDTH dial:

2) Remove the four flat head screws on each side of the front panel that hold the panel assembly to