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  MaxTrac 900 Trunking to Conventional Conversion
By Robert W. Meister WA1MIK
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These are the steps required to convert a 900 MHz MaxTrac mobile radio from trunking to conventional, for amateur use.

The radio was a two-channel 12-watt trunking radio, model number D27MQA5GB2AK. The front panel has two pushbuttons: System and Sub-fleet, as well as four LEDs: Sys 1, Sys 2, Sub A, Sub B. All 900 MHz MaxTracs use a logic board with a 16-pin accessory connector as well as a socketed firmware chip (PROM or EPROM). As the radio was trunking only, I did not test it for transmitter output power. Trunking radios have several test modes built-in, but the truth is, I forgot about them and I didn't feel it was necessary.

The same procedure can be used on 30-watt or multiple (6, 8, 16, 32) channel radios by choosing the proper model and panel numbers during initialization.

The mandatory steps consist of replacing the firmware, blanking the logic board, and initializing the logic board. Changing the front panel escutcheon is done merely for convenience. This entire procedure could take 30-60 minutes.

There are additional articles on this web site by Scott KBØNLY, that also go through the blanking and initialization procedure.

NOTE: If your trunked radio has sufficient conventional modes for your use, you can skip the process of replacing the firmware, blanking and initializing the radio, and just use trunking or conventional software to program the radio.

IMPORTANT NOTE: You can save yourself a lot of time and effort, especially if the radio is already working properly or you don't have the necessary test equipment to do a full initialization. Before you replace the firmware, use regular programming software, enter the Service menu, Board Replacement. Go through ALL the steps (you won't see any data on the first step - F2) and write down all the values you see for the transmit power, frequency warp, power amplifier (16 values), deviation (16 values), and all of the total deviation settings. Don't make any changes; just press F10 to exit each screen and go through each one in sequence. Then replace the firmware and blank the board. During initialization, just enter the values you wrote down in the various places as you go through the steps in sequence. You'll still have to enter the voltages, but everything else can be set where it was originally. I've developed a sheet that you can use to record these values; it can be downloaded as a PDF file here.

Replacing the Firmware:

You should try to purchase the FVN4019A conventional firmware from Motorola. Last time I ordered it, the cost was $25US, but Motorola was never able to deliver the part. After waiting several months, I canceled the order and took an erased 27C256-20 EPROM and programmed it with an image of the conventional firmware, obtained elsewhere. This is a 32kByte binary file which completely fills the EPROM. I replaced the trunking PROM with the new EPROM, by following these steps:

  • Remove the front control head screws with a Torx T15 driver.
  • Remove the four side case screws with a Torx T10 driver.
  • Remove the radio's bottom plastic cover.
  • Pop the metal shield off the microprocessor area on the logic board.
  • Remove the existing trunking firmware PROM.
  • Install the conventional firmware chip, taking care to position it properly.
  • Here's what the logic board looks like:

    After removing the shield, here's where the firmware PROM/EPROM is. Note that pin 1 is in the upper left corner of this photo, just like the other big IC next to it. The board has "1" silk-screened on it next to the socket; you can make it out next to pin 1 of the other big IC. Installing it backwards will likely ruin the chip, as well as stop the radio from functioning (yes, it has happened).

    Replacing the Escutcheon:

    If your radio has a conventional escutcheon already, you can skip this section. But while the radio is apart, now is a good time to change it. Refer to the photos above to identify the cables:

  • Unplug the speaker cable from the logic board.
  • Unplug the two control head cables from the front of the logic board.
  • Remove the four Torx T10 screws holding the display board to the inside of the control head.
  • Carefully remove the display board from the control head.
  • Remove any plastic or silicone buttons that remain in the control head.
  • With a blunt tool (large screwdriver tip or pliers), press on the two plastic studs on the inside of the control head that hold the escutcheon in place. You just have to loosen them a bit. Once they're flush with the inside of the control head, you can remove the escutcheon from the outside or push them out a bit further with a smaller tool.
  • Clean the front of the control head, especially in and around the area where the escutcheon sits. I use a small screwdriver and an old toothbrush. Remove the volume knob and clean underneath it as well. Use a paper towel dampened with some household cleaner.
  • Install the new conventional escutcheon by pressing it in from the front until it's fully seated.
  • Clean the buttons and place them back into the control head. I use a paper towel dampened with alcohol.
  • Clean the display board with a brush if necessary. Wipe the LEDs off with a paper towel dampened with alcohol.
  • Reinstall the display board into the control head, securing with the four T10 screws. Make sure the cable retainer is put back and does not short out the display board.
  • Plug the two control head connectors back into the front of the logic board.
  • Plug the speaker cable back into the logic board.
  • Blanking the Radio's Logic Board:

    Connect a power cord and a programming cable, turn on the radio, the RIB, and the computer. I started MaxTrac LAB RSS and went through the following steps:

  • F2 - Service
  • F8 - Blank Logic Board
  • F3 - Normal code plug, retain tuning data.
  • F2 - Continue. 64 blocks of data got written out.
  • F10 as needed to exit the program.
  • It really doesn't matter if you choose to retain the existing tuning data or not, because the tuning data is only maintained if the SAME program blanks and initializes the radio in the same programming session. In our case, we're using one program to blank the radio and another to initialize it. You could select the extended code plug, since that's what the radio will end up with, but using F3 above will take less time since only 64 code plug blocks get written to the radio. You need to blank the radio in order to initialize it as a new conventional model. Any and all code plug data (i.e. mode information) will also be cleared out by this process.

    Initializing the Radio:

    I connected the radio to my modulation analyzer through a 30dB, 50-watt attenuator. I applied a 1VRMS, 400 Hz audio tone to the audio input wire on the RIB. I had a digital multi-meter available for the various voltage measurements. I started regular MaxTrac RSS, and went through the following steps. User input is shown indented.

  • F2 - Service
  • F6 - Board Replacement
  • F2 - Logic Board
  • ...... Product: MaxTrac High Signaling
  • ...... Model Name: MaxTrac 100 [ see NOTE 1 below ]
  • ...... Range: 896-941 MHz
  • ...... Model #: D27MJA73A6_K: two-channel, 12-watt, TPL and DPL, Signaling, Accessories, Talk-around [ see NOTE 2 below ]
  • ...... Panel #: 000 [ see NOTE 3 below ]
  • ...... Serial #: 10 characters from the label on the back of the radio
  • F8 - Program: 320 blocks of data got written out.
  • F2 - Logic Board
  • F2 - Reference Crystal Data [ see photo below ]
  • ...... Temp: 25.0C
  • ...... V-Diode: 2.72V as measured on pin 43 of the microprocessor U802.
  • ...... V-9.6: 9.60V as measured on pin 1 of the logic board-to-RF board connector.
  • Click on this photo to see a larger, more detailed, image.

  • F8 - Program
  • F3 - Transmit Power
  • ...... F6, up/down, F6, set to 12 watts (80 -> 68)
  • F8 - Program
  • F4 - Warp Reference Frequency
  • ...... F6, up/down, F6, set to 902.5000 (38 -> 34)
  • F8 - Program
  • F5 - Transmit Power Calibration
  • ...... F6, up/down, tab, F6, set to 12 watts on all test frequencies
  • F8 - Program
  • F6 - Transmit Deviation Calibration
  • ...... F6, up/down, tab, F6, adjust to 2.5 kHz (17 -> 50)
  • F8 - Program
  • F7 - Total Deviation with TPL
  • ...... F6, F6, left at 15
  • F8 - Program
  • F8 - Total Deviation with DPL
  • ...... F6, F6, left at 15
  • F8 - Program
  • F2 - Continue
  • F10, F10, F10 to exit to main menu.
  • NOTES:
    [1]: The two-channel radio is a MaxTrac 100. A multiple-channel radio is a MaxTrac 300.
    [2]: Choose the appropriate model based on the number of channels and output power.
    [3]: The two-channel radio panel number is 000. A multiple-channel radio panel number is 001.

    The radio has now been completely initialized. I turned the radio off, disconnected the power cable, replaced the shield over the microprocessor on the logic board, put the plastic cover back on, and secured the control head to the front of the radio.

    Program the Modes:

    With regular MaxTrac RSS, I was now ready to program the two modes for the two local 900 MHz repeaters. You may desire different options and settings. Note that I used the SHIFT-NUM method to enter frequencies; if you do a lot of out-of-band programming you might want to hex-edit the MDF file accordingly. User input is shown indented.

  • F3 - Get/Save code plug
  • F2 - Read code plug from radio. 320 blocks read.
  • F10 - Exit
  • F4 - Change/View code plug
  • F2 - Radio-Wide Configuration
  • ...... Timeout: 180 seconds
  • ...... Handset: N
  • ...... Emergency Alarm: None
  • ...... ACC internal: None
  • ...... ACC External: General I/O
  • F10 - Exit
  • F5 - Mode Configuration
  • F8 - Mode Utility
  • ...... Add (parameters already setup to add one conventional mode).
  • ...... F8 - Execute. Repeat this step for each mode of your radio is a multiple-channel model.
  • F10 - Exit
  • ...... RX Frequency: (shift)927.48750
  • ...... TX Frequency: (shift)902.48750
  • ...... RX Squelch: TPL
  • ...... Tone: 192.8 Hz
  • ...... RX Signaling: 00
  • ...... TX Squelch: DPL
  • ...... Code: 311
  • ...... TX Signaling: 00
  • ...... Busy Channel Lockout: N
  • ...... Hear-Clear: Enable
  • ...... Low Power: Disable
  • F4 - Next Mode
  • ...... RX Frequency: (shift)927.41250
  • ...... TX Frequency: (shift)902.41250
  • ...... RX Squelch: TPL
  • ...... Tone: 100.0 Hz
  • ...... RX Signaling: 00
  • ...... TX Squelch: DPL
  • ...... Code: 311
  • ...... TX Signaling: 00
  • ...... Busy Channel Lockout: N
  • ...... Hear-Clear: Enable
  • ...... Low Power: Disable
  • ...... Repeat these steps for each mode if your radio is a multiple-channel model.
  • F10 - Exit
  • F3 - Get/Save code plug
  • F7 - Save code plug to Archive
  • ...... Enter customer ID
  • F8 - Write
  • F8 - Write Backup
  • F8 - Save code plug to Radio
  • F2 - Continue
  • F10 - Exit to main menu
  • F10 - Exit program
  • That's it. The computer can be turned off and the RIB and test equipment can be disconnected.


    The radio produced 12.0 watts on both transmit frequencies of 902.41250 MHz and 902.48750 MHz. The VCO was out of range and the receiver wouldn't hear anything unless it was unsquelched, then it heard signals on 927.41250 MHz and 927.48750 MHz just fine. HearClear WAS enabled on both channels; its effect could plainly be heard on the recovered audio.

    The VCO will be opened up, carefully tuned to receive the 927-928 MHz portion of the band, and resealed. This procedure can be found in this companion article.

    Equipment Utilized:

    I don't own a service monitor, but I have all the separate pieces of equipment that would be contained in one. You will need to measure RF power, FM deviation, and frequency. You will need a source of audio to set the deviation, as well as an accurate digital multi-meter. Of course, you'll need a computer with the appropriate software, a RIB (Radio Interface Box), and the proper cables for your computer and the MaxTrac.

  • HP 8901B Modulation Analyzer for measuring output power, frequency, and deviation.
  • Narda 50 watt, 30dB coaxial attenuator, as a dummy load for the 8901B.
  • HP 204D Audio Oscillator to provide modulation audio into the RIB.
  • Fluke 189 digital multi-meter to measure DC voltages.
  • Astron RS-12M power supply set to 14.00 VDC.
  • Computer (running MS-DOS), RIB, and associated cables.
  • Manuals and Other Documentation:

    Motorola MaxTrac 900 MHz Trunked 12 watt Service Manual, 6802977G10.
    Motorola MaxTrac 900 MHz Conventional 12 watt Service Manual, 6802980G40.
    Motorola MaxTrac Radio Service Software User's Guide, 6880900Z03.

    Useful Part Numbers:

    If you're going to do a "proper job" as the British would say, you might as well make sure all the visible parts are present, clean, and unbroken. Here are some of the parts that I keep on hand for rebuilding MaxTracs, as they're commonly damaged, worn, or missing:

    Part DescriptionPart Number
    Two-channel conventional escutcheon1380276L02
    Multiple-channel conventional escutcheon1380277L01
    Top or bottom plastic cover1580127L01
    Small, flat-head T10 screws on sides of radio (20/pkg)0310943R55
    Volume control knob with white dot3680144M01
    DC power connector on rear heat-sink0980255E01
    Mini-UHF female antenna connector on rear heat-sink0980131M01

    Note that replacing the DC power connector or antenna jack requires removal and disassembly of the power amplifier. These parts should be replaced if broken or worn to the point of non-functionality. The DC power connectors cost over $11US in 2005 and can only be purchased through Motorola.

    Acknowledgements and Credits:

    Thanks go to Scott KBØNLY for proofreading the article and suggesting photo opportunities.

    MaxTrac, PL, DPL, HearClear, and a whole lot of other things are trademarks of Motorola, Inc.

    Contact Information:

    The author can be contacted at: his-callsign [ at ] comcast [ dot ] net.

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    This article first posted September 2006.

    Article text, photographs, and conversion to HTML © Copyright 2006 By Robert W. Meister WA1MIK.

    This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.