©1999 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 4/29/04
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Digital circuits have signal levels
near ground for a lo logic level and
near +5V for a hi logic level. On the
schematic diagram, a bar over the
function name at an ic indicates the
active logic level is lo; if no bar, the
active level is hi (majority of signals
are active-hi).
Relative audio signal levels for full
modulation are shown for the mixer
circuit on the schematic diagram.
Test Points.
There are a couple of handy test
points which may not be obvious.
The long top lead of R25 is con-
nected to the collector of the optocou-
pler in the autopatch circuits. You
can connect a meter to that point to
check if the ring detector is working,
and you can short that point to
ground to simulate a phone ring
condition. However, note that a timer
in the computer prevents the phone
ring signal from activating the
corresponding reverse autopatch
responses more than once within a
few minutes; so it may be necessary to
reboot the computer to repeatedly test
the reverse autopatch functions.
Alarm input J9 can be simply
shorted to ground to test the alarm
circuit.
With a good scope, you can
observe the addressing action of the
computer by connecting a probe to
pin 37 of the 6803, which is the least
significant bit of the address bus. Be
careful not to short to adjacent pins.
The clock speed is close to 1 MHz; so
you need to set the scope time base
accordingly. You can observe changes
in the addressing pattern with
changes in operating conditions, such
as opening the squelch. If the pattern
doesn't change regardless of stimulus,
the computer may not have booted
properly or may have crashed for
some reason.
Another method of checking to see
if the computer is running properly is
to check the watchdog timer circuit.
Observe either the pulse train at bit 2
of port 2, on pin 10, of the 6803 or the
dc timer voltage at pins 11-12 of J4 to
see if the watchdog timer is being con-
stantly reset by the microcomputer.
If the computer doesn't seem to be
running, and the front panel TONES
led doesn't respond to touch tone in-
puts, check the crystal oscillator with
a scope at pin 3 of the 6803 to be sure
it is running.
Current Drain.
Current drain is relatively low in
idle condition. With the transmitter
off, the current drain for the receiver
and controller, which are the only
modules drawing current, should be
about 260 mA (about 88 mA with the
low power CMOS microcomputer and
EPROM option). If you have a crystal
oven(s), they require an additional 25-
50 mA at idle and up to 400 mA when
cold. With the transmitter on, current
drain will be 3 to 4 Amp, depending
on power level.
Fuse Circuit.
Fuse F1 and crowbar diode CR7
provide limited protection against
short circuits and negative transients.
If a power supply with current
foldback is used, the diode may even
prevent damage if the power supply is
connected backwards. And the diode
can absorb many reverse voltage
transients. It is always a risk, but if a
short circuit occurs, hopefully, the
fuse will blow before any damage to
the wiring or pc board occurs.
If it is necessary to change the
fuse, unsolder the old one from the
top of the board, and replace it with a
new 7 amp type GJV pigtail fuse. If
you can't find one, you can solder
your own leads to the end of a regular
type AGC plug-in fuse.
MAINTENANCE.
CAUTION! Do not operate the
transmitter without a 50 ohm load or
antenna connected. PA damage may
result. The transmitter is keyed
whenever the receiver squelch is open.
Handling IC's.
Note that most of the ic's are static
sensitive. The warranty does not
cover static damage; so handle them
with care. A grounded wrist strap
should be worn whenever cmos parts
are handled. Even after assembly, it
is possible to damage cmos parts if
static builds up from walking or
sliding a chair on a carpet, etc.
Always use precautions when
handling a board with cmos parts.
Replacement EPROM.
The EPROM is light sensitive.
Excessive exposure to sunlight or even
strong room light eventually may
erase the chip. Normally it is not
necessary because of the cover on the
compartment; but if you expect the
chip to be exposed to strong light for
many days, cover the window on the
EPROM with a sticker of some sort.
If you want to change call letters,
touch tone codes, or default parame-
ters, we can burn a new EPROM for
you. The cost is $20, plus shipping.
Please enclose a completed
questionnaire like the one you filled
out when you ordered your repeater.
Also, please specify the name and zip
code used when you ordered the
repeater, since we only support
registered owners and we need to find
your original records on the computer.
Should you transfer ownership of the
repeater at any time, please contact
us to change registration to the new
owner.
Yearly Checkup.
About once each year, you should
check several things on the repeater.
The transmit and receive frequen-
cies should be recalibrated, since all
crystals age a little. Refer to receiver
and exciter manuals for procedures.
Use an accurate service monitor or
signal generator and frequency
counter.
The vswr and power output should
be checked both at the input to the
duplexer and at the antenna to be
sure that the antenna system is in
good condition. Since antennas
typically are subjected to weather
conditions and flexing from wind, it is
a good idea to inspect the antenna
and tighten any loose joints. Also
inspect any weatherproofing on coax
connections.
Exciter & PA Tuning.
The exciter and power amplifier
both must be aligned properly both to
prevent desense and to protect the
transistors from damage. (See "Before
you turn on power..." section on page
1.)
The exciter and pa should each be
carefully tuned into a 50 ohm dummy
load, using exact procedure defined in
manuals for those modules.
Power Level.
Rf output level must be set accord-
ing to the procedure in the power am-
plifier module manual. It is important
not to overdrive the pa, but to operate
at the level recommended in the in-
structions so you can operate
continuously without overheating.
On the other hand, it is not
necessarily better to underdrive the pa
by a substantial amount, because
