Radio Shack TRS-80 Service Manual page 116

HEAD RADIAL ALiGNMENT/CE ALIGNMENT
1. Insert a 5 1/4" alignment diskette.
2. Connect Scope:
Channel A to TP 1
Channel 8 to TP 2
Ground to TP 10
Ext. Sync to TP 7
Set mode to add (A
+
8) Invert 8
Vert. to 50 MV/div
Trigger external· loosely.
3. Read track 16 and verify the "cat eyes" pattern as
shown in Figure 11. The smaller of the two "eyes"
should not be less than 75% amplitude of the
other.
%
=
(small lobe/larger lobel x 100.
4. Step to track tJ0. Return to track 16 and re-verify
the pattern.
5. Step to track 34/40 and return to track 16. Re·
verify the "cat eyes" pattern.
If Radial Needs Adjustment:
a. Loosen the two retaining screws on back of the
unit and the retaining screw on the carriage as-
sembly.
b. Turn the Adjustment Cam until the "cat eyes"
pattern is within 75%. If the pattern does Iiot
come within spec, loosen the hex head screw on
the collar of the stepper motor and rotate the
stepper motor shaft until the "eyes" are to the
75% level. Tighten the hex head screw and return
to step a.
EQUAL AMPLITUDE
'''nT,m 161
c. Tighten all screws and recheck adjustment.
TIME SCALE - 20m.c Dill
FIGURE 11. "CAT EYES" PATTERN
RETAINING MODULE ADJUSTMENT
SCREW""'_rr._ CAM
01¥\'
ILre
o
FIGURE 12. RADIAL ADJUSTMENT
109