Highfields Amateur Radio Club
Constructors Corner.
smoking soldering iron
copyright date

Home build an OPC-118 replacement cable.
By Brian, MW0GKX.

I was asked (anonymity respected) if I knew how to connect an IC-756 to an AT-500.

Recent Icom transceivers (like the 756) are fitted with ACC(1) (8 pin DIN) and ACC(2) (7 pin DIN) sockets to provide accessory connection but the AT-500, an older Icom design, uses a 24 pin Molex connetor for its' connection.

The +8V reference voltage, band voltage, SEND signal, ALC and ground are all available on ACC(2) socket which is what was required for the AT-500.

To interconnect their earlier products fitted with the 24-pn Molex ACC socket to the newer equipment with the 8 & 7 pin DIN sockets Icom used to offer the OPC-118 adapter cable. This has not been available for a while now and I soon discovered what signal was required at what pins for these 2 items to work together and here is the answer for everybody.

If you have the original Molex to Molex lead you can store it away for later use (or take off the radio end plug and wire accordingly to a 7 pin DIN plug if you wish).

Parts List

P1 Molex 24 pin (4 rows of 4 pins, 0.145" (3.68mm) pitch) Molex part No.03-06-2242 available at Digi-Key UK (I'm in the UK but it should be available locally to you wherever you are and from other suppliers). You will also need 5 Molex 02-06-2103 pins for this plug (Digi-Key has a minimum order of 10 for the pins).
P2 7 pin DIN plug.
Some 4 core plus shield cable (enough to reach between the radio and accessory).

Making Up

See the diagram below for connection detail nd use the shield of the cable for ground. Don't forget to slip the 7 pin DIN cover onto the lead before you start.

The Molex pins will require crimping but they could be soldered if you so wish. Once they are connected to the wire slip them into the correct hole in the plug casing. Once pushed fully home they should stay fitted.

The plugs in the picture are viewed looking into the mating face and the functions are:

Of course your wire colours may vary from this.
cable layout

After checking the soldering is good and there are no shorts or stray whiskers, assemble the 7 pin DIN plug and you're ready to go. Make sure you plug into the ACC(2) on the radio with the 7 pin DIN.

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