MT-4E VHF & UHF Receiver & Transmitter Instruction Manual
IM08-MT-4E-TXRX-P1162
VHF & UHF Hardware Tuning and Troubleshooting
20
Transmitter Amplifier
Set the front panel switch on the transmitter to KEY TX and check that the transmitter output power is
approximately 0.5 to 8.0 W for VHF and UHF models.
Check the following pins on Connector J1 (while the transmitter is keyed):
Pin
Signal Monitored
Typical Voltage
1
RF Enable / Power Control (+0.5 to +3.0 VDC
corresponds to 0.5 to 8.0 W RF Power Output)
+0.5 to +3.0 VDC
2
Reg9.5 VDC from motherboard
+9.5 VDC ± 5%
3
Voltage from mothe13.8 VDC line
+13.8 VDC**
If Pin 1 is not within tolerance, the most likely fault is in the UDB or synthesizer module. If Pins 1, 2
and 3 are within the specified tolerances and there is no RF output power, the most likely fault is in
the amplifier.
To test the RF power amplifier sub-assembly, set the output power to maximum using “Power Level
Adjustments” in RSS Service mode, and drive the input of the amplifier with a 0 dBm RF signal. Check
that the RF power output is 8.0 W when the front panel switch is set to KEY TX.
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If the radio system is not receiving or transmitting on the right frequency, check the Channel and Bank
Select lines of the receiver and transmitter modules. The motherboard has jumpers that allow one of
16 channels to be selected on a receiver or transmitter. The factory default is to have them all set to
ground the channel select lines CSEL 0 through CSEL 3, forcing the radio to operate on Channel 1.
On the receiver and transmitter there is also a Bank A/B line which usually floats high – selecting
Bank A. The receiver and transmitter have separate control of their channel select lines, so changing
receiver channels does not affect the transmitter channel.
If the Radio Service Software is failing partway through a read or write of the receiver, check that the
receiver is not squelching and unsquelching repeatedly during the read or write operation. Disconnect
the RF signal source from the receiver during the read or write operation.
** Refer to the Specification Data Sheets (located in this manual)
for the full Supply Voltage range.
