Repair of Goldmund 18.4 amp

Hi guys,

Lately, i have some  issues with my goldmund 18.4 amp. It needs to be serviced. I sent it to the local techinian but he told me that he needs a symmetric diagram of the circuit to repair.
I bought it from secondary market and it is too costly to send it overseas for repair.

Anyone can help to provide the symmetric diagram and any advice on how to go about it?

I desperately  need help to repair it.

Your great help is highly appreciated.

Thank you,