I do not have the complete inside schematic diagram for repairs.
All I have is the diagram for the external connections which I sent to you today.

The Terra 720 is an old radio. Heavy. Maybe OK for winch driver or the crew vehicle.
You might find better used handheld radios on eBay.com

DEC 2, 2014: See these used ICOM IC A4 units for $125 on eBay. Very simple. (I am not the seller.)

http://www.ebay.com/itm/Icom-IC-A4-V...:SS:SS:US:3160

Connect a VHF handheld radio to a tall Larsen 5/8 wave magnetic mount antenna on top of your vehicle for much greater range. (A proper antenna is the secret!) Find at:
http://www.cumulus-soaring.com/larsen.htm