[aprssig] RC-D710 Problem

[Gary]

A friend is about to start a long trip and has been struggling to get his
new APRS setup working before he leaves. It consists of a RC-D710 fed
position data from a Nuvi 350 using Scott's GTRANS cable. The RC-D710 is
also connected to an Alinco DR-605 transceiver via an RPC Electronics
interface and cable set that RPC built especially for him to use with the
DR-605 radio. While RX is working fine and stations are listing on the head
and GPS, transmit is not working at all. I've jumped in and double checked
all menu settings on the head, even tried testing the PTT by jumping the PKS
and GND terminals at the head side of the RPC Electronics interface box. The
radio changes modes fine (Rx to TX) but even though BCON is enabled on the
head the open collector switch in the head never seems to pull PKS to ground
thus keying the radio. We've tried changing METHOD back to MANUAL in the
head then using the BCON button to manually key the radio but no joy. We're
back in AUTO mode on the head with flashing GPS, BCON is enabled, APRS12
mode, etc. Any ideas why the RC-D710 isn't keying the radio? The head is new
but I suppose it remains possible that the T/R switching transistor is
faulty but we hope not.
73,
Gary