Radio Shack TRS-80 III User Manual

PART 4
MAINTENANCE
PHYSICAL DESCRIPTION OF THE PC BOARDS
The Logic PC board is approximately 6 inches (152 mm)
long by 5.5 inches (139 mm) wide. Figure 10 illustrates the
placement of test points and connectors.
CIRCUIT BOARD TEST POINTS
The following test point description assumes that the Logic
and Servo P.C. boards are installed in the Drive and that the
Drive is in an operational mode with a diskette installed:
Logic Ground (TP6)
Digital Logic ground is referenced at TP6.
Differentiated Read Signal (TP3, TP4)
These test points are provided to observe the differ-
ential
output of the second stage amplifier and differ-
entiated read signal.
Read Data Single Shot (TP5)
The output of the single shot used in the read section is
nominally 1.0 fJ.sec for each flux transition detected.
Index Pulse (TP7)
With a standard soft sectored diskette installed, the
signal is a high going pulse, nominally 4.0 msec in dura-
ation every 200 msec.
Amplified Read Signal (TP1, TP2)
These test points are provided to observe the differ-
ential
output of the first stage of read signal amplifi-
cation.
Motor On (TP13)
This signal is low true for the "motor on" condition.
Track G0 (TP8)
This signal is low true when the carriage is positioned
at track 00 and the step motor phase is correct.
Analog Ground (TP10)
The analog ground reference point is provided for
measuring read/write waveforms.
Step Pulse (TP12)
When stepping in or out, the signal is a high going pulse
for each step of the carriage.
Write Protect Switch (TP9)
When a write protected diskette is installed in the Drive,
the signal is high.
OPTION SE LECT
Input Line Terminations
The Disk Drive has been provided with the capability of
terminating the input lines listed below:
* Motor On
* Direction Select
* Step
* Write Data
* Write Gate
These lines are terminated through a 150 ohm resistor pack
installed in a DIP socket located at IC location 2F.
In a multiple drive system (Catalog Numbers 26 -1163/1164/
1161) only the last drive on the interface is to be termi-
nated. All other drives on the interface must have the resis-
tor pack removed. Catalog Number 26-1164 is shipped
with the termination resistor installed. Catalog Numbers
26-1161/1162/1163 are shipped without a resistor pack.
105

Radio Shack TRS-80 III Specifications

General

Brand	Radio Shack
Model	TRS-80 III
Category	Desktop
Language	English