PTT Not Working

[barkerg]

I had this software working a few years ago using the ShareGPS android app on a smartphone transmitting to an HC-06 bluetooth transceiver with its TXD pin wired to the RX pin of an Arduino Nano. The Nano is then connected to a Friendcom FC-301D transceiver which requires a ground on its PTT pin to transmit, so the 3 HX1 PTT HIGH and LOW values in the code need to be reversed. I just tried to revive this project after it sat on the shelf but the radio will not transmit. The smartphone is paired to the HC-06 and ShareGPS is showing a 3D fix and is Connected to the HC-06 as shown in the ShareGPS Connections tab and the HC-06 LED switches from blinking to steady. The radio's transmitter works if I manually ground the PTT pin so I know that is ok. I then took the radio out of the circuit and monitored the D4 pin of the Nano but it always shows 5V, never going near 0 even though APRS_PERIOD is programmed for 10 seconds. I can toggle the D4 voltage using a modification of the blink program, so I know that is ok. Where is the code located that triggers the PTT function? How else can I troubleshoot this?