Advanced Instruments 4D3 - Stir Driver Noise

The Advanced
®
3D3/4D3 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).
A ferrite bead placed in line with the
Darlington emitter (Q2B) does clean up the
square wave for problems, as shown in fig-
ures 2, 3 and 4.
The most serviceable place to install the fer-
rite bead is inside the head cover on the white
wire exiting the head shaft and attaching to
TR1 on the head transition board. Order
Advanced Instruments part #91035 to get the
appropriate ferrite material.
Stir Driver Noise
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.