Modifications for the Kenwood TM-251

This is the wide-banding modification for the Kenwood TM-251E
From: Anders, LC3HAT -
Author: Robert Vea. GM7AVE -

This is an update to the original file sent out. Hopefully this one gets out un-corrupted. There are no changes to the mod listed so if you have previously modified the radio OK, then you do not need this file.

The Mod...

This is the wide-banding modification for the Kenwood TM-251E

This file is written by Robert GM7AVE, who performed this mod to a friends radio. Be careful if you decide to do this mod. Check if this mod is valid for your model before doing it. You may contact me at:

The mod begins...
  1. Remove both lids,
  2. Remove facia, knobs and vfo nut,
  3. Remove the screw between the volume and squelch pots,
  4. Remove the LCD, carefully, the connectors are fragile,
  5. Remove the cage, it is held on by 4 screws,
  6. Remove the 2 screws holding the control unit in place,
  7. If fitted now remove the memory expansion and CTCSS boards,
    The memories will still be there when you are re-building.
  8. Now read this carefully, VERY VERY GENTLY pull of the control unit, this has 2 small connectors holding it in place.
    If you are not careful enough, this PCB will flick off into orbit, and possibly be damaged.
  9. Here we are, getting the soldering iron ready...
  10. Locate D417 on the PCB. It is the one at the edge of the board, very close the IC401 which is a MD6433388F (Opposite side to knobs.)
    To confirm this diode is the correct one, check using a digital meter that one end is connected to pin 60 of the above chip. The other end should be connected to pin 65 of the same chip VIA a 100ohm resistor.
    Remove this diode. Check to see if the wire links are attached. If they are (I don't expect them to be) then remove them. These are marked W1, W2, W3 on the PCB.
  11. Go have a cup of coffee now, then come back and put the radio back together again.
  12. Do a CPU reset by powering up with MR pressed (Bye memories!)
    Note: Sometimes a CPU reset isn't required, so do not do this initially, only do a reset if the radio malfunctions in some way when powered up.
  13. Oh look, the radio will now receive and transmit from 136MHz to 174MHz, and also receive from 300Mhz to 470MHz.
  14. If you also look at the menu's avaiable you will see a new one.
  15. End of mod. Did you succeed or kill the radio? Let me know ok?
Mail to Robert Veal on FORTH VIEW BBS (0131 660 6680)
E-Mail to
Mobile telephone - Voda 0468 176788
GM7AVE @ GB7EDN (MRSGB) Stingray Systems(1996)

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