Fluke Biomedical 875 Victoreen - Manual (Page 36)

Maintenance, Calibration, and Troubleshooting
Metering Circuit
5
TEST push button to provide a convenient input signal. Voltages at these points should be measured with
no signal input.
5-5
onnect the cable conn urn the function switch to
TP502 under two con s: 1) with no signal input; 2) with a
ut obtained by p the CHANNEL T button.
1. Disc ecting the readout module to the detector. T
TEST.
2. Measure the voltages at TP501 and dition
signal inp ressing EST push
The voltages should be:
No Signal Channel Test Signal
TP501 + -2.8 V
TP502 -1.5 V +
5 V
6.3 V
These voltages are approximate and actual value ffer somewhat. Any marked departures from
these values is an indication of a malfunction.
5.6 Metering Cir
The signal circuit that dr er whose output on pin
9 should equal its input
These signals vary from button pressed.
All other faults in the me s.
ard contains a
ower supply whose voltage is critical. It
asure 6.2
± 0.001 V at TP401. It may be
(P/N 876A-1-75, Schematic 876A-1-3B)
ils, so for troubleshooting purposes, it will be
re similar for troubleshooting purposes. E.g.
the simplest way to eliminate certain problems is to replace printed circuit board 876A-1-75. Where the
tood, but completely analogous procedures apply to the high alarm circuit. At some points, it is
deeme s
h
In
w
s
curren pin 1 of U502 is -9.9 V (low) and the voltage at the same point is + 13.7 V when high.
s at
critical points in the signal chain between test point TP502 and relay K501:
s may di
cuit (P/N 876A-1-3E, Schematic 876A-1-92)
ives the meter is U401 (Figure 5-2). This is a voltage follow
on pin 10.
-1.5 V with no signal to +6.3 V with the CHANNEL TEST push
tering circuit should be detectable by resistance measurement
NOTE
The preamplifier metering bo
regulated p
should me
adjusted by R413.
5.7 The Alarm Circuits
The alert and high alarm circuits differ only in very minor deta
sufficient to discuss them together. As a matter of fact, they a
discussion is given in terms of particular pin numbers for definiteness, the alert alarm circuit is to be
unders
d sufficient to describe the voltage state as simply high or low; at other points, particular voltage
ave been given. The maximum high value is +15 V, and the minimum low value is -10 V.
the alert alarm circuit, if a measurement can be made directly on a pin of an OP AMP, a high reading
ill u ually be close to +15 V, and a low reading close to -10 V. For example, the normal (low input
t) voltage on
However, if the voltage is measured on the other side of the resistor R510, the high is only +1.45 V,
whereas the low is still the same -9.9 V.
If the Channel Test has shown the system to be operative, the following will be the voltage state