I just installed a Protel WA 4000 with a mars coin validator and a TSG Inc keypad. At first everything seemed to be okay but now the pay phone has an open line and will not hang up even when the handset is in the cradle. Any troubleshooting suggestions would be greatly appreciated.

Are the hookswitch contacts shorted?

Disconnect one hookswitch wire. Test hookswitch with a multi-meter
by setting the meter to ohms & placing one lead of the meter on the
disconnected hookswitch wire & the other lead on the connected
hookswitch wire. When hookswitch lever goes on & off-hook, the
meter should show signs of resistance. If the meter reads the same
when hookswitch lever goes on & off-hook, replace the hook-switch.

Hi, The hookswitch tested okay. When I first hang up the phone the line closes and then opens back up without touching the phone.

Have you discounted a Telco line issue with your butt set or a S/L set?

The lines are okay. I did notice an electrical smell inside the pay station days after this started but thought nothing of it. Also the handset has very low receive audio. Maybe the board somehow got fried?

Not good when you let the smoke out of circuit boards. A short or incorrect voltage?

I am not sure, as far as I know I did nothing to short it and the voltage has not changed. I left the board connected to the telco line and disconnected the coin validator, the key pad and the coin relay and still had an open line. So I am guessing it might be the board.

Looks like it's pointing that direction.