Have a Bridgeport BOSS 5 system (original) that has recently stopped accepting programs through the RS232 connection.
BEFORE
The system worked fine and communicated with the PC without any problems. Upon hitting the Bport 'edit' button the TeraTerm (Hyperterminal-type communication app) window would display the proper BOSS 5 > Input * sequence. Programs would be transferred and run properly.
CURRENTLY
TeraTerm window is selected with the correct COM port. Machine set to Set Up, Reset-Clear toggle switch is pressed. Wait a few seconds. Hit Edit button and the Edit light comes on the display panel (like it is supposed to). no response. Have set echo on to verify anything that is sent. Get nothing. Do not get BOSS5 > Input prompt. The Edit light remains lit and machine locked out until the Reset/Clear switch is hit. All Bport boards have been reseated and it does not help.
I have replaced the 1488 and 1489 chips (twice) on the ERS board but no prompt.
I have verified through a RS232 loopback test that the COM port on 2 different PC are verified to work correctly. Each PC has been tested and echos information back to itself in the TeraTerm window.

I can control the machine while in Set Up. All axis move and respond properly.

Anything else I am missing here? Is the ERS board fried? What else to look for?
Any troubleshooters have any ideas?