In a message dated 4/27/1999 11:31:12 PM Eastern Daylight Time,
mcsalem@... writes:
<<
Mike:
I had to stop and think for a minute since it has been some time since I
tuned up
an MX, but there really is not much to do to tune up the transmitter. For
the
later versions of these radios, Motorola made a separate service manual and
a
troubleshooting manual. Tune up instructions are in the service manual. I
do not
have a service manual for a crystal controlled MX, but do have tuneup
instructions
for a PX-300 crystal controlled which is the PT version and also manuals for
the
PX-300-S. I have service manuals for the UHF and VHF MX radios.
For the crystal controlled PX (MX), the tuneup instructions start with R107
which
sets the power. Then you set the channel elements on frequency, CE101 to
CE108.
Then you adjust R102 for deviation with a tone in the microphone.
If it is a synthesized model, you have to set the VCO by tuning the radio to
the
highest and lowest frequency and measure the voltage at Pin 12 of U14. For
the
UHF radio, the high frequency control voltage should be set no higher than
4.8
volts. For the lowest frequency, the control voltage should be set no less
than
1.8 V. The adjustment is to L4. You should also check this for the highest
and
lowest frequency for the receiver and make sure that the voltage is in the
same
range. As a practical matter, I found that the VCO would lock from 1.0 V
to 7.0
volts, but I suspect that it would not cover the temperature range of the
radio.
I would set it right in the ham bands and use the upper end to reach into the
public service frequencies to monitor and not program the transmitter.
For VHF, the voltage range is 1.4 Volts low and 4.75 volts on high. The coil
adjustment and pin 12 of U14 is the same.
After this, you set the frequency and adjust R107 for the appropriate power
level: 1.0 Watt, 2.5 Watts, and 6 watts for VHF and 1.0 Watts, 2.0 Watts,
and 5.0
Watts for UHF.
I hope this is helpful.
73
Micheal Salem N5MS >>
Thanx, it is very helpfull.
Mike
