The Advanced
®
Model 3250/4250 Service Manual
45
Excessive noise in the stir amplitude and fre-
quency can affect the quality of the stir signal
and introduce excessive pre-freeze errors or
cause poor freeze pulse repeatability. The
presence of such noise can best be determined
with the use of an Oscilloscope.
1. Connect the Oscilloscope between J9-1
and ground.
2. Turn on the instrument. If there is a
Supervisor/Operator keyswitch, turn it to
the Supervisor position (if required).
3. Press TEST. Press < or > to select “Stir/
Freeze Test”, and then press START.
4. At “[stir] [freeze]”, press <.
The stir wire driver signal should be a clean,
square wave at approximately 72 Hertz and
4Vdc (see figure 1). If not, verify that two
ferrite beads are present in your unit, as
shown in Installation Option A or B, below.
If the beads are missing, purchase Advanced
Instruments Part No. 91035 and install, as
shown.
If the beads are present and you still have
noise as shown in figures 3 or 4, replace the
driver transistor PCB522.
Stir Driver Noise
(Serial Suffix A - C, only)
Figure 1. Good signal.
Figure 2. Can be cleaned up with ferrite bead.
Acceptable if stir wire not affected.
Figure 3. Not acceptable. Replace stir wire driver
or use ferrite bead.
Figure 4. Not acceptable. Replace stir wire driver
or use ferrite bead.
To Next Page
Loading...
Need help?
General
