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Motorola MTX900 portable radio. Most of these radios were used by municipalities and utility companies. They could be missing knobs, antennas, have engravings, and possibly cracked housings. However, due to rugged design, the internal components are usually not damaged. Housings, knobs, batteries, and chargers from Genesis series: P200, HT600, MTX800, MTX810, MTX820, and MT1000 radios will work with the MTX900. Front covers of Genesis series radios are interchangeable. Internal speaker components and connections are different on some models. The 900mhz antenna is not interchangeable with other Genesis radios due to frequency range. 12 button keypads were available on some models as shown in photo. Radio must be capable of CONVENTIONAL and trunked modes to rx simplex frequencies. The radio shown has its discriminator audio ported out the accessory connector and through a modified speakermic cable. A small mono male plug terminates end of cable. |
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Four machine screws are removed when disassembling the radio. Two machine screws in the metal base are loosened but not removed during disassembly and reassembly. Highly recommend checking hole alignment of housing and front cover before fully tightening any screws. |
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MTX900 circuit board before modifications. This view is looking at the back of the radio with shield removed. Motorola Service manual 68P81069C30-O was used as a reference. Count from RIGHT side of connector P1, note pin 5 and pins 9-10 are where the discriminator taps will be taken. Pin 5 is from the discrminator output, pins 9-10 are ground. Pins 9-10 are soldered together at the factory. Used a magnifying glass when soldering as the pads are small. |
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Pins 1 and 2 on accessory connector (top of radio) are used to output signal to a modified speakermic. Photo shows pinout of accessory connector as viewed from top of radio. Since a regular speakermic wouldn't be used on this radio again, foil between (Pins 1-2) was de-soldered and cut with a hobby knife.
Heat shrink tubing was placed over lead ends going to accessory connector after photo was taken.
Didn't want exposed conductor wire on blue and red leads to touch circuit board foil or components.The radio's receiver range is 935-941 mhz. Frequencies can be changed with MTX900 Radio Service Software, a programming cable (can be made using 15 pin d-sub and speakermic connector.), RIB, and 386/486 computer. Transmit frequencies were disabled as radio is used only for receiving 900mhz simplex frequencies. (No scan) |
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Motorola MTX900 and Griffin iMic connected to laptop USB port. |
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