Teledyne 4250 Installation And Operation Manual page 155

Following are suggested areas to check before attempting to
service the 4250's circuitry. Telephone consultation with Cus-
tomer Service is strongly recommended. Look for the following:
1. Verify that the problem is in the flow meter and not caused
by the area-velocity probe, probe cable, Quick-Disconnect
Box, power supply, or other equipment connected to the
flow meter.
The flow meter could be all right and will appear to mal-
function because of clogged or leaking tubes or other com-
ponents; check these first. Pay particular attention to
the connectors and cable from the submerged probe.
2. Check all 3 fuses to see if they are blown (see Figure 5-9).
3. Check the battery or power supply.
Proper voltage to the unit should be from 10.5 to 14.5 VDC.
If the unit is powered from the AC supply, make sure the
branch circuit is delivering at least 110 VAC to the power
supply cord.
4. Check the wiring harnesses, connectors, and solder joints.
Under normal conditions these should stay in good condi-
tion. However, physical stress, or operation of the unit with
the door open or the desiccator saturated could cause corro-
sion of the connectors in certain atmospheres.
5. Look for physical damage.
Burnt, broken, or overly hot components, stuck or inopera-
tive switches, or water damage, may be apparent if you
look closely.
6. Look for shorted or open diodes and transistors, especially
driver transistors.
7. Check the voltage regulators.
The output voltage from the regulators should be within
5% of their rated value. Check to see that rated voltages
are available at various places on the boards.
8. Look for excessive current draw from some or all the cir-
cuitry.
This will usually be accompanied by an unusual amount of
heat coming from some component or group of components,
and the voltage on the power rails may well be depressed.
9. Check the input signals to the unit and see that they are
correct.
This may require the use of an oscilloscope. You may need
to consult Customer Service for the proper appearance of
wave forms.
10. Check to see that the crystal oscillator is operating and at
the proper frequency.
11. Check the reset circuitry to see that it is working properly.
4250 Flow Meter
Section 5 Maintenance and Service
5-15