PacComm TINY-2 - Troubleshooting Guide

TROUBLESHOOTING
Crystal
Oscillator
Adjustment
TROUBLESHOOTING
The
PacComm
packet
controller
is
a
complex
piece
of
electronic
equipment.
Servicing
must
be
approached
in
a
logical
manner.
The
best
preparation
for
troubleshooting
is
to
study
the
detailed
hardware
description
above.
While
it
is
not
possible
to
present
all
possible
problems,
symptoms
and
probable
cures,
this
section
of
the
manual
will
give
direction
to
troubleshooting
based
on
our
experience.
Press
all
socketed
ICs
into
their
socket
along
each
edge.
If
there
is
any
sign
of
corrosion
on
any
IC
pins,
remove
each
IC,
one
at
atime,
and
bumish
the
pins.
Often
simply
removing
and
reinstalling
the
ICs
will
cure
intermittent
problems
caused
by
vibration
or
humidity
affecting
the
IC
sockets.
Inspect
all
solder
joints
for
a
smooth
shiny
appearance.
A
dull
gray
appearance
may
be
an
indication
of
a
crystalized
solder
joint.
Use
a
small
soldering
iron
designed
for
printed
circuit
work
and
resoider
the
connection.
Remember
that
all
the
logic
circuits
operate
at
standard
TTL
levels
(a
“low’
is
less
than
plus
0.4
V
and
a
"high"
is
greater
than
plus
2.4
volts),
and
all
digital
inputs
.and
outputs
switch
between
these
two
levels.
Thus,
if
you
see
logic
signals
switching
between
0
and,
say,
1
volt,
you
can
be
sure
there
is
a
problem
(usually
a
short).
On
the
other
hand,
do
not
mistake
switching
transients
on
digital
logic
lines
for
improper
operation
--
these
show
up
as
ringing
and
other
distortions.
Verify
that
there
is
activity
on
the
control
bus
READ
and
WRITE
lines,
the
GHIP
ENABLE
lines
on
the
memories
(U2
and
U8
pins
20),
the
IOREQ
fine
on
GPU
(U1)
pin
20
and
the
INT
line
on
CPU
(U})
pin
16.
Each
of
these
lines
should
show
activity,
and
if
any
line
is
quiet
this
is
a
sign
of
trouble.
Address
and
data
line
problems
may
also
show
up
as
tack
of
activity
on
the
control
bus
lines,
especially
the
chip
selects.
Check
each
of
the
16
address
and
8
data
lines
for
activity.
Any
lines
showing
a
lack
of
activity
are
not
operating
properly.
If
you
suspect
problems
with
address
or
data
lines,
try
removing
ail
the
memory
chips.
Each
address
and
data
line
will
now
show
a
distinct
pattern.
The
address
lines
should
be
(possibly
distorted)
square
waves
whose
periods
increase
by
a
factor
of
two
on
successive
lines
as
you
step
line
by
fine
from
AO
to
A15.
Logic
lines
that
show
no
activity
may
often
be
traced
to
a
short
on
the
pc
board,
probably
due
to
a
defective
solder
joint.
Follow
the
instruc-
tions
above
tor
inspecting
solder
joints.
If
you
decide
to
use
an
ohmmeter
to
check
for
shorted
lines,
use
a
low
voltage/low
current
test
instrument.
(Most
modem
DVMs
are
fine
for
this.)
Ifin
doubt,
remove
any
ICs
connected
to
the
lines
you
are
measuring.
If
you
suspect
a
short,
check
the
high
density
areas
of
the
PC
board
for
the
problem.
In
most
cases
the
short
will
be
found
there.
If
an
oscilloscope
is
not
available,
then
a
voltmeter
can
help
you
find
serious
difficulty
on
digital
signal
and
address
lines.
Set
the
meter
for
the
scale
where
a
full
5
volts
can
be
displayed.
A
reading
of
1.5
to
3.5
anna
irien
nnRneenn
nO
TINY-2/MICRO-2
Technical
Ref.,
2
Ed
©
1989,
PacComm,
Inc.
17