metrotech 220A, need help !

[jubeco01]

Hi guys ! I´ve got an old metrotech 220A in relatively external good shape but all the wires messed up, adjust potentiometer does not look original (has a 50 K Ohm tv volume potentiometer) , original 2000 ohms headphones ok, but I have tried to solve the wiring to meter and battery with no luck! does any one have a picture of the inside and wiring?

thank´s for help !

P.D
this pic is the way I found it