Based on community discussions and circuit descriptions, users typically explore the following: Frequency Expansion/Amateur Radio Conversion
Here are some popular mods and upgrades that TK-M707 owners have successfully implemented: Kenwood Tkm-707 Mods
For full circuit descriptions, alignment procedures, and board views to assist with repairs, the Kenwood TKM-707 Service Manual is the primary resource for technical specifications. Kenwood TKM-707 Instructions Manual | PDF - Scribd Kenwood Tkm-707 Mods