Radio Shack TRS-80 Service Manual page 115

PREVENTIVE MAINTENANCE
To ensure that the Disk Drive operates at its design poten-
tial, the only scheduled preventive maintenance required is
periodic cleaning of the magnetic recording head.
Mechanical and electrical adjustment details are provided
for further sclVice as a result of disassembly or repair.
CLEANING THE HEAD
To clean the magnetic head, use a lint-free cloth or cotton
swab moistened with 91% Isopropyl alcohol. Wipe the head
carefully to remove all accumulated oxide and dirt. Dry the
head using a lint-free cloth.
CAUTION: Rough or abrasive cloth should not be used to
clean the magnetic recording head_ Usc of cleaning solvents
other than 91% Isopropyl alcohol may damage the head.
Extreme care must be exercised to prevent the heads from
being damaged (i.e" scratching. banging together. etc.).
ALIGNMENT AND ADJUSTMENT
To perform the alignment and adjustment procedures,
you will require the following equipment:
'*
30 MHz Dual Trace Triggered Sweep Scope
'*
5 1/4" Alignment Diskette
' *
51/4" Blank "scratch" Diskette
DRIVE MOTOR MAINTENANCE
Long Term Motor Speed Adjustment
1. Check power to unit. (+12 VDC + G.6V. and
+5
VDC ± G.25V.j
2. Insert a blank diskette and activate the drive.
3. Under fluorescent lighting, observe the speed disk
on the spindle pulley. For 60 Hz operation the
outer ring on the speed disk should appear station-
ary. For 5(;1 Hz operation the inner ring should
appear stationary.
4. If the speed disk does not appear stationary, adjust
R4, located on the Servo PCB, until the disk
appears stationary.
5. If motor speed cannot be adjusted, repair Servo
PCB or motor as required.
108
Instantaneous Speed Variation Check/RAW Data Check
1. With a blank diskette inserted, write a 2F pattern
on any track.
2. Connect scope to TP 5 with:
Vert. to 2 volts/div.
Time Base to 1.usec/div.
Trigger internal/positive
3. Observe the waveform. Measure jitter on the lead·
ing edge of the third pulse. The leading edge of the
pulse should start 8,usec
±.
240nsec from the
trigger pulse. The third pulse fitter should be less
than 480nsec (edge to edge).
____c::: __c::: __
==Jfr
4. If jitter is el<cessive, replace drive belt, motor,
Servo PCB, or spindle as necessary.
CARRIAGE MOVEMENT CHECK
1. Step between tracks 00 and 34/40.
2. Check carriage movement. Be certain that carriage
is moving freely and not binding at any point.
Repair if necessary.