I "think" that is Hitachi , same board as the roadtalker 40 base.
I found this on the net.
Compare it to the radio you have and see if it looks the same on your board before you attempt anything, but it is all I see for a fine tune mod.
Proceed with caution.
Copy and paste:
CLARIFIER MODIFICATIONS
1)Find the green wire coming off the FINE TUNING control.Follow the wire to the pc board where it connects and unsolder it.
2)Find the RED wire behind the meter display and solder it to that location(there is 8VDC there)
3)Find the BLACK wire from the FINE TUNING control and unsolder it from the PCB.
4)Solder this wire to PC GROUND .
5)Find the PURPLE wire from the FINE TUNING control and unsolder that from the PC board.
6)Solder this wire to the point on the PC board where R303 and the cathode,the end with the band around it! , of D301.
This mod will give you about 3khz up/down off the "channel".
If you move the clarifier and the radio "drops out" you will need to JUMP d301 and put the purple wire back to where it was.
73
Jeff