Tandy 1000 Technical Reference Manual

Tandy 1000
3-3-2. Function of Variable Resistors
Technical Reference Manual
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 RS. Also some types of DD motor Ass'y
have not the variable resistor Rl 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).
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 20Omsec±4msec (see Fig.3lS).
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 TP5 or at the READ DATA output signal during
read operation. Then adjust the variable resistor so that the read
data asymmetry in Fig.32l takes the minimum value. For a double sided
FDD, repeat this operation alternately for side 0 and side 1 heads to
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Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200