ICOM 4088SR (HM-75 Speaker Mic) Tuning Solution
Refer to 4088 SR Service manual for more tuning detail in conjunction with Tuning box.
To make Tuning box, attach the following resistors to RING of 3.5mm jack and ground via switches:
3.5k = 'B' Key in manual (Change Tuning Item)
7k = 'A' Key in manual (Lock in Tuning)
12k = 'Up' In Manual (use to change Tuning Item VALUE/Select channel to tune)
24k = 'Down' In Manual (use to change Tuning Item VALUE/Select channel to tune)
To set radio into tuning mode, open radio and connect 'Test' pad to ground, then power up.
Make sure that you press the 'A' key/switch to lock in tuning once finished.