Modifications for the Kenwood TM-2550
The TM-2500 series radios may be easily modified for use on MARS/CAP
frequencies from 141-150.995 MHz.
Locate the control unit (X54-1860-XX) on the bottom of the radio. This is
the same board that the TU-7, and or MU-1 are mounted on. Just to the
left of IC3 you will find a row of diodes. Cut diodes D8, and D11. After
the diodes have been cut you will have to "reset" the microprocessor.
All of your programmed data such as memory channel data, DCL data, and
Phone number data will be erased and you will have to reprogram them. If
the radio is not reset, it will not recognize that you have cut the two
Press and hold the [PS] key.
Turn ON the power switch.
Release the [PS] key.
TM-2550 DCL Call Sign Data
Some owners of the TM-2530/50/70 have reported a loss of the DCL system
call sign data when the power switch is turned off. The call sign data
actually remains in memory, but timing prevents its utilization in some
radios. Adding a resistor will correct this problem.
If you receive a radio that exhibits this symptom add a 47K ohm resistor to
IC3 to the Slave CPU on the control unit (X53-1440-XX) between pins 4 and
20. Cover the resistor leads with "spaghetti" type insulation. Adding the
resistor to radios that do not have this symptom will not cause any
problems, so you may wish to add the resistor if you receive a radio for
service for some other problem.
Before soldering unplug the DC power cable and antenna from the radio.
When soldering to this IC you must use a soldering iron that provides
voltage isolation on the tip since IC3 is a CMOS device and can be easily
damaged by static electricity or voltage on your iron. Use normal CMOS
precautions. One final precaution: Don't bridge any of the pins on the IC
with excess solder!
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