DIP Switches in Yaesu FT-2700RH Dual Band Transceiver

Discussion in 'Radio Circuits, Repair & Performance' started by NG6R, Mar 1, 2011.

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  1. NG6R

    NG6R Premium Subscriber QRZ Page

    I have a Yaesu FT-2700RH 2m/440 dual-band transceiver with 440 MHz front-panel-selectable step sizes of either 12.5 kHz or 25 kHz. I am unable to key up repeaters on frequencies “in between” those intervals. (E.G., I can dial in 450.0000, 449.9875 and 449.9750, but not the frequency I need, 449.980.) If I try to use the closest frequency to the one I need, the audio is a little distorted and, worse, I can’t key the repeater. I’d like to modify the radio to have a 5 kHz step size.

    A brief article appearing in mods.dk, but with no author identified, showed a table of DIP switch values for the FT-2700 (same general configuration as the FT-2700RH???), which enable a user to select different configurations. Here is an excerpt from that table, showing positions of three DIP switches (D13, D14, D15) and corresponding frequency ranges and step size options. (Part of the table I didn’t show has four other DIP switches controlling similar options for the 2m band.)

    0 0 0 --NO WORK
    0 0 1 --430-440 MHZ 12/25
    0 1 0 --430-450 MHZ 12/25
    0 1 1 --430-440 MHZ 5/10
    1 0 0 --*NORMAL* AS SHIPPED
    1 0 1 --430-440 MHZ 12/25
    1 1 0 --430-440 MHZ 12/25
    1 1 1 --430-450 MHZ 5/10

    If I could, I’d pick the last option. I took the radio completely apart, as much as I could. I could not find those DIP switches anywhere!! Has anyone ever located these switches, if they exist? I have the operating manual that talks about different versions of the 2700RH and with various band ranges and step sizes. But, I don’t have the service manual. I didn’t spot them on the schematic, either.

    If you have the service manual or have any experience with locating these DIP switches, I’d really like to hear from you. Thanks.

    73, Jerry, NG6R
  2. NG6R

    NG6R Premium Subscriber QRZ Page

    “D” = Diode, not Dipswitch!!

    Thanks to a suggestion from my buddy, Deane, N5DQ, I went back inside looking for diodes instead of dipswitches. They were well hidden under the add-in “floating” optional board, visible in the second figure. As you can see in the third figure close-up, the sole diode is mounted in position D13, corresponding to the *NORMAL* AS SHIPPED entry in the table above.

    I will now carefully remove the PC board, so as to get access to the reverse side, and install diodes in both remaining positions, D14 and D15. (Or, just tack-solder them onto the front side if the board proves too difficult to remove.) This will correspond to the table's bottom (1/1/1) position of wider frequency range (which I don’t need) and smaller frequency step sizes (which I do need).

    I’ll report back on the results whenever that task is completed. I may still need the service manual to get the 1Nxxxx number of this D13 diode, although for this application, the exact replacement number probably isn’t critical.

    73, Jerry, NG6R

    Attached Files:

  3. KE3WD

    KE3WD Ham Member QRZ Page

    The ubiquitous 1N4148 or 1N914 or equivalents should work fine.

  4. NG6R

    NG6R Premium Subscriber QRZ Page

    Modification complete

    Diodes were purchased and the modification made. The attached photo shows the additional two diodes soldered in place (soldered from the top of the board, without removing the control board). Following Clark’s suggestion, 1N914 diodes were used. They are not only readily available, good for logic applications such as this, but very inexpensive (package of 20 for $1 from a local electronics parts store.)

    After modification, frequency step sizes on the 70 cm band are 5 and 10 kHz, instead of 12.5 and 25 kHz. Although not needed, the frequency range has also now been increased to include 430 – 440 MHz.

    73, Jerry, NG6R

    Attached Files:

  5. NG6R

    NG6R Premium Subscriber QRZ Page

    Afterthought and Caveat

    I did not attempt to experimentally confirm the complete accuracy of the configuration table shown earlier in this thread. While it may be accurate, it seems counterintuitive that three of the configuration entries all show the same result. Entries 0/0/1, 1/0/1 and 1/1/0 all show 430-440 with 12/25 step size. If anyone has either experimented to see if this table is correct or has another documented source confirming these results, please consider posting that information here. The data in this table came from a 1998 mods.dk article with no author identified.

    I can only attest that the last (1/1/1) configuration entry is correct. However, in making modifications based on any other entry from this table, one should proceed with due caution.

    Perhaps you have the same radio and are thinking about making this same frequency step mod. If so, you might consider replicating/confirming the other entries in this table, PRIOR to permanently soldering in the diodes, and then post the results here. (I was in too much of a hurry to fix my radio to even think about the usefulness of such an experiment!)

    73, Jerry, NG6R
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