Fluke PM6690, Service Manual, Page: 117 / 200

n
Adjustment
– Connect the probe tip to the center hole of J7.The sur-
rounding holes are suitable ground connections. See Fig-
ure 7-2.
– Adjust R196 until the pulses on the oscilloscope look
the same. See Figure 7-3. Use a screwdriver type of ad-
justment tool.
– Check Step Response X1 , repeat Step Response X1 and
Linearity several times if necessary.
Repeat all steps above for Input B on the timer/counter. Con-
nect the probe tip to J9. Adjust R268.
Sensitivity
n
Setup
– Keep the settings on the counter from
Linearity .
n
Adjustment
– Connect the DMM to the test points X34 (+) and X35
(-). See Figure 7-2.
– Adjust R197 until the DMM reads +17 ± 0.2 mV. Use a
screwdriver type of adjustment tool.
Don't forget to resolder the RF shield.
Power Supply
n
Setup
– Do as described under Preparations above.
– Select default settings by keying in USER OPT
®
Save/Recall
®
Recall Setup
®
Default
n
Adjustment
– Connect the DMM to test point X9 and ground (metal
shield lid over input amplifiers). See Figure 6-4 and
Figure 7-4.
– Adjust the +5 V trimmer on the AC/DC power supply
board with a screwdriver type of adjustment tool until
the DMM reads +5.10 ± 0.005 V.
– Check that the voltage from the AC/DC power supply at
X26 is +15 ± 0.7 V.
– Check that the voltage from the AC/DC power supply at
X21 is -15 ± 0.7 V.
Note: Adjusting the +5 V does not affect other settings in the
instrument.
External Reference Input
n
Setup
– Do as described under Preparations above.
– Select default settings by keying in
USER OPT
®
Save/Recall
®
Recall Setup
®
Default
– Connect a 1 MHz sinewave signal with amplitude 0.1
V
rms
(0.28 V
pp
) into 50
W
from an LF synthesizer to the
external reference input. Use a 50
W
termination on the
input.
– Set an oscilloscope with X10 probe to 10
m
s/div,
100 mV/div (including probe) and AC coupling.
n
Adjustment
– Connect the probe to X19. There are two ground pads in
the vicinity. See Figure 7-5.
– Adjust C442 to maximum amplitude. Use a screwdriver
type of adjustment tool.
Power Supply 7-13
+5 V adj.
J17
X26
X9
X21
GND
AC/DC BOARD
RF SHIELD
Figure 7-4
Adj5 V and ch15 V and -15 V.
C442
X19
GND
GND
AC/DC BOARD
J22 J25
J23 J26 J21
Figure 7-5
Adjusting the external reference input.