PacComm TINY-2 - Page 142

TROUBLESHOOTING
Other
symptoms
or
P3-TTL),
the
cable
and
Max
231
(U15)
again.
Finally,
be
sure
that
the
computer
actually
uses
levels
less
than
-3
voits
and
greater
than
+3
volts
for
signal
levels.
0
and
+5
volts
witl
not
work
unless
the
TTL
port
is
used.
Other
symptoms
TINY-2/MICRO-2
appears
dead
If
no
LEDs
wink
during
the
startup
cycle
the
problem
is
more
serious.
Check
to
see
that
the
crystal
oscillator
is
working
(4.1952
MHz)
and
that
the
signal
appears
on
the
output
of
U7
(74HC4060)
pin
9.
The
clock
signal
is
a
(possibly
distorted)
square
wave
signal.
Aiso
check
for
clock
signals
Z80
CPU
(U1)
pin
6
and
SIO
(U14)
pin
20.
Verity
that
the
battery
backed-up
RAM
protection
circuit
is
working
by
measuring
that
pin
28
of
the
RAM
(U8)
at
least
+4.7
voits
after
input
power
is
applied.
If
the
unit
is
operating
and
accepting
commands
from
the
terminal,
an
overall
check
of
the
CPU
complex
may
be
conducted
using
the
HEALTH
command
(see
Operating
Manual.)
Modem
won't
key
transmitter.
Check
to
see
the
commands
XMITOK
and
TXUIFRAM
are
ON
.
If
the
transmitter
doesn't
key,
the
problem
is
most
likely
in
the
connecting
cable,
or
a
carrier
present
(DCD)
indication.
If
DCD
is
active
and
the
command
FUlldup
is
off,
the
controller
will
not
activate
the
keying
line.
If
this
is
the
problem,
see
the
DCD
section
below.
If
the
connections
appear
to
be
in
order,
check
8440
(14)
pin
17
for
keying
(PTT)
transitions.
If
nothing
is
seen
on
pin
17,
either
software
or
digital
hardware
are
faulty.
!fpin
17
is
active,
trace
the
signal
through
74HC14
(U17)
pin
9
to
U17
pin
8
(now
inverted)
to
the
gate
of
the
keying
FET(Q2).
The
FET
output
line
changes
from
high
impedance
to
low
when
a
keying
signal
is
present.
This
can
be
checked
with
an
ohmeter.
Uncopyable
transmitted
packets
If
other
stations
seem
unable
to
decode
your
packet
transmissions,
it
is
possible
that
your
transmitter
is
being
overdriven.
Listen
to
the
sound
of
your
TINY-2/MICRO-2
transmissions
on
another
receiver.
Extremely
weak
signals
indicate
inadequate
modem
output.
Refer
to
the
Transmit
Level
Adjustment
Procedure.
You
may
also
be
able
to
hear
the
beginning
of
transmissions
clipped
or
weak
if
inadequate
transmit
delay
(RXD
command)
is
being
used
for
your
transmitter.
You
can
confirm
that
the
digital
logic
and
modem
on
the
packet
controller
are
operating
properly
by
performing
an
Analog
Loopback.
if
the
loopback
works
properly,
then
re-set
the
output
level
taking
care
to
set
the
drive
level
lower
than
previously.
Note
that
direct
connection
to
typical
microphone
inputs
requires
the
drive
trimpot
to
be
turned
to
near
the
minimum
signal
position
for
proper
signal
levels.
if
the
Analog
Loop-
back
fails
to
operate
properly,
perform
a
digital
loopback.
If
this
test
operates
correctly,
the
CPU,
software,
and
SIO
are
operating
correctly
and
the
modem
circuit
is
suspect.
i
TINY-2/MICRO-2
Technical
Ref.,
2
Ed
©
1989,
PacComm,
Inc.
21