Teac FD-55 Series, Maintenance Manual

Page: 38 / 216

On the PCBA MFD control and the PCBA DD motor servo, maximum two
variable resistors are mounted.
The PCBA MFD control of some PCBA versions and some revision numbers
has not the variable resistor R5. Also some types of DD motor A s s ’y
have not the variable resistor R1 on the PCBA DD motor servo.
However, there is interchangeability in function and performance
between these PCBAs with the variable resistor and without the
variable resistor as far as they have the same parts number (8 digits)
and the same version number (2 digits). It is not necessary to identify
one from another as the spare parts.
The variable resistors are correctly adjusted before the shipment of
the FDD and fundamentally they shall not be readjusted except for by
a trained technicians.
(1) Rl on PCBA DD motor servo (Disk rotational speed adjustment)
Variable resistor for adjusting the rotational speed of the disk.
It is adjusted so that the index pulse interval at TP4 or at the INDEX
output signal is 200msec±3msec for FD-55A ^ F and 166.7msec±2.5msec for
FD-55G (see Fig.315).
For the DD motor Ass’y without the variable resistor Rl, the rotation
speed of the motor is fixed by the ceramic oscillator in the servo
circuit and no adjustment is required.
(2) R5 on PCBA MFD control (Read data asymmetry adjustment)
Variable resistor for adjusting the asymmetry of the read data pulse.
Some PCBAs have this variable resistor and others have fixed resistor
instead of it.
For a PCBA with the variable resistor, R5, write IF data and observe
the pulse intervals at TP 5 or at the READ DATA output signal during
read operation. Then adjust the variable resistor so that the read
3-3-2. Function of Variable Resistors
330