Curtis Computer kb4900 - Troubleshooting and Support; Field Troubleshooting Guide; KB-4900 Limited Warranty Information

OPERATION UN +12 VDC:
Your
KBv48OO can be
operated
from
+10 TD +14 Vdc
batteries or
from
a mobile
power system.
You can
also use a
+12
Vdc
battery
continuously
connected for
battery backup
in case
of ac
power
failure. With the
battery
voltage
at or
below about
12
V
there should
be little drain
as
long
as the
unit is
powered
by
ac.
Connect the
battery
cable to the
KB-4900 before
applying power
to the
other end or
you may
get
a
spectacular
short if the
center
pin
of
the RCA
plug
hits the
(grounded)
chassis! In
any event, place
an
inline 1
Ampere
fuse in the
battery
supply
line for
safety.
You can reduce
the
battery
current drain
by
half
by
removing
the
meter illumination
lamps.
CIRCUIT FUNCTIONS:
The KB—4900
consists of
an 8035
microprocessor.
a 2732 32K
bit EPRDH
for
program
storage
and a
2114 4K bit RAM for
sending
bufier and
message
memory storage.
An
B044 is used for the
keyer
section.
A 74LSlb4
is used for the
keyboard
"X" matrix
scan. Two 74LS75’s
are
used to latch the
EPRDM and RAM
addresses.
A
74LS175 serves
to latch
the lower four
hits of
port
2. Three lLD—74
dual
optical
isolators isolate
the
paddle
key,
manual
key
and RTTY
loop.
A 74LS3O
B-input
NAND
gate
is used to
detect a hexadecimal OFFH on
the
latched address
lines.
This is NORed with
the write
signal
from
the
processor
to
develop
a strobe for
writing
to an
external
parallel
ASCII
monitor.
If
you
have
the
real-time clock
option.
three
HC1451B dual BCD
counters
divide the
4OOkH2 ALE
frequency
to 0.4Hz. This
signal,
{ed to the
B035
port
17, provides
the clock
reference.
CALIBRATION:
Normally, your
KE—49OO
will not need
calibration
over the life of
the
unit
however
you may
touch
up
the
settings
if
you
desire.
1.
Haximum
speed
limit:
This
parameter
is set
by
adjusting
a
trimmer
labled "R1" and
located on
the small PCB
located
on the
rear
panel
of the unit.
It is the
only
trimmer on
the
board and is
accessable
by
simply
removing
the
four screws
holding
the
bottom
wrap-around.
You can
adjust
the maximum
speed
(when
the
speed pot
is
full clockwise)
by
rotating
the
trimmer
until
the
speed
meter reads
your
desired
maximum.
2.
Speed
meter
calibration:
A trimmer
on the
keyboard
PCB controls the
calibration o!
the
metering
circuit.
Connect an
oscilloscope
or
pulse
measuring
counter to
pin
14 of the 8044
IC. Set the
speed
pot
to
give
a
reading
of 48
ms. for
cycle
length
when
the dot
key
(or
CTRL—8) is
depressed
(dot is 24
ms., space
is 24
ms.). Then
adjust
the
trimmer
marked “s” on
the
keyboard
PCB. This trimmer
is
accessible from
the
top
or
bottom of the board.
hen the
speed
meter
reads 50
upm,
the
adjustment
is correct.
(You will NOT HEAR
dots
during
this test
if
you
use CTRL-E.
They
are muted.)
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