Fluke Biomedical 956A-201-M2 - Manual (Page 86)

5-8
Signal Transmission, Detector (Factory Test Only)
High voltage is to be disconnected for this procedure. Channel
power is to remain on. Refer to schematic 897A-210-13.
1. Using a DVM, measure the discriminator voltage between pin 9 and pin 8 of Z1. Zero to +2 V should
be obtained by adjustment of R44. If not, zener diode CR11 or Z1 may be faulty.
2. Connect a pulse generator to the junction of R17-C10 and ground. Adjust the pulse generator output
for a 50-microsecond pulse of -5 V amplitude with a frequency of 1 kHz.
3. Using an oscilloscope, verify pulse transmission. Pulses should be present at Z1 pin 14, R23, Z1 pin 7
and pad G. If not, locate the point where pulse transmission is terminated and replace the defective
component.
Before continuing, measure the anti-jam setpoint voltage at pin
10 of Z1 and ground. Record this value. If a malfunction is found
in this section, the faulty component should be replaced and the
setpoint readjusted to its original value.
4. Remove the pulse generator. Connect a DC power supply across R25 (+) and ground (-). Connect a
DVM at pin 13 of Z1. The output should be low. Increase the power supply slowly until pin 13 changes
from the low to the high state. If this does not occur, Z1 is defective.
5. If the above output state change is present, connect the oscilloscope to pin 2 of Z1. A square-wave of
approximately 50 kHz should be observed when the output of Z1, pin 13 is high. If not, isolate the
faulty component and replace it.
6. Set the high voltage to the operating point of the G-M tube. Using an electrostatic voltmeter, measure
the high voltage at the pad labeled HV with respect to chassis ground. If high voltage is not present,
check for broken wiring or a high voltage supply failure at the UDR.
7. If all previous steps indicate the electronics are functional, the G-M tube needs replacement. This
requires that the detector be sent to the factory for recalibration.
Check Source, Detector (Factory Test Only)
If the check source meter movement does not operate, perform the following steps.
This test requires continuous activation of the check source
control at the UDR.
1. Using a DVM, measure the DC line (+15 Vdc) at pads J and H. If 15 Vdc is not present, check cable
connectors for broken wires. Detector pad H is on when the check source is actuated. Pad J is on
when the check source is not actuated. Also determine if the check source circuitry at the UDR is
functional.
2. If the DC voltage is available, the meter movement, with integral check source capsule should be
replaced.
WARNING
CAUTION
NOTE