Repairing the Antenna Switch In the MN-2700 Antenna Tuner

By: Lee Cramer, WB6SSW

I recently acquired an MN2700 that had a "fried" antenna selector switch. Apparently, the previous owner tried switching antennas while transmitting.

The antenna selection switch consists of a two sided ten position ceramic switch wafer, with five of the twelve positions used. One side selects one of the four antennas or the dummy load. The other side grounds the non-selected antenna. In my case it was the "selection" side that had two adjacent switch contacts that were melted. The "grounding" side was fine.

The correct switch wafer is no longer available, but fortunately, the switch wafer is a standard size. Therefore, most any ceramic ten position wafer will work if it has six adjacent switch contacts. All that is needed is to piggyback the new wafer onto the existing wafer. The new wafer "selects" the antenna and the old wafer continues to "ground" the unused antennas.

Wiring is somewhat tight between the switch and the SO259 connectors. Fortunately, Drake was kind enough to mount the SO259's from the outside. Therefore, its easy to simply unscrew the SO259 first, then, pulling it away from the chassis, apply the soldering iron to the connection.   The same procedure applies to the fiberglas wire antenna terminal board, unscrew it first, then unsolder it.

Once the existing wafer is removed, mount the new wafer in front of it, and bridge the old contacts to the appropriate contacts on the new wafer.   Drake used 14 gage bus wire to wire this switch.

Remount the switch, then remount and resolder each antenna connection.   Resolder the ground connection and the tuner connection and your done.

73,   Lee, WB6SSW