Philips aw7150/01p problem

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Hello.
I have an old Philips aw7150/01p - stereo radio cassette recorder. I want to add it a line in connector. I will solder the line in wires on the potentiometer pins. The problem is that I don't have the tape mechanism anymore and I don't know what pins should I short on the motherboard to make the amplification start in the tape mode. For the moment it's working only in the radio mode, but it's not a solution to mix the radio sound with the sound from the line in. I presume that the radio switch is doing the same thing - powering the amp circuit but I don't know which are those pins. I presume the info is in the service manual, but I don't have one.

Could you help me, please?

Thanks a lot.