Zenith H-100 Service Manual page 78

5-162
OSCILLOSCOPE METHOD
The oscilloscope method of write precompensation adjustment
is primarily used to adjust the H-207 for non Heath/Zenith
disk drives. To understand the relationship that exists
between the PRECOMP switch setting of DS1 and jumper JO.
refer to the table below. This table shows how to set the
PRECOMP switch of DS1 and JO for the particular system you
are working on. Now perform the following steps to adjust
write precompensation. Refer to the illustration at the
beginning of this section for the locations of the test
points.
DESIRED RESULTS
TYPE OF ORIVE
Precomp Precomp Precomp
no tracks
all tracks tracks >43
*
8" Double-Density
N/A
Precomp : I1l Precomp· : 1
JO : X
JO - X
5-1/4". 48 TPI. Precomp : 1 Precomp : 0
N/A
Doub1e- Dens lty JO : X JO • X
5-1/4", 96 TPI, Precomp
=
1 Precomp : 0
Precomp
=
1
Double-Density JO : IN JO : X
JO
=
OUT
*Precomp is bi't 4 in the control latch
X : Don't Care
NOTE: Precomp is automatically disabled in single-density operation.
Set the PRECMP 2 control (R4) to a fully clockwise
position.
Set the PRECMP 1 control (R3) to a fully counterclockwise
posi tion •
The position of J2 will determine which of the two following
procedures you will use when adjusting write
precompensation. Refer to the manufacturer's suggested
write precompensation value for the type of drives in
~he
system. If the system has only 8" disk drives. or only
5-1/4" disk drives. or the 8" write precompensation figure
is less than the 5-1/4" write precompensation figure, use
the procedure under "J2
=
8
<
5". If the system has disk
drives where the
8"
write precompensation figure is greater
than the 5-1/4" write precompensation figure, use the
procedure under "J2
=
8
>
5".
Typical values of precompensation are:
5-1/4" disk drives
8" disk drives
125 to 200 nS
125 to 175 nS
typical 150 nS.
typical 135 nS