Tonight I rewired the phono inputs, added ground lugs to the new I/O board, and wired the CD and AUX inputs across the Unused Loudness Switch.
Some problems developed.
1- The PAT-4 is quiet - NO HUM - across the TUNER, TAPE, and SPARE Inputs.
2- I now have a 60hz hum (low) on the PHONO.
I used shielded cable for the PHONO inputs. I connected the shielding to the ground terminal on the selector switch and the ground terminal on the RCA Jack.
Since the ground of the Phono RCA Jack on the I/O strip was not connected to the other grounds I added a ground lug and connected the Phono Grounds to this new Chassis ground. I also added a ground lug to the other end of the I/O strip since they did not appear to have a connection to the chassis ground.
Did I inadvertantly create a Ground Loop? If so which connection would be the best to disconnect? If it helps the I/O board is the one from Roy Mottram.
3- My idea for switching the extra input through the Loudness Switch does not appear to have been a good one. I now have a bit of cross-talk between the CD and Aux (one input connected to the bottom of the switch and the other to the top, with the selector switch to the middle contacts. I will probably remove the connection and drop one input, connecting the AUX directly back to the selector switch. Unless someone has an idea to eliminate it.
Thanks in advance for any ideas