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Question about a Sony STR-av1020 receiver 1990.

I am looking for the service manual for the STR-AV1020 receiver.
Any help would be appreciated. My receiver is missing a front knob and i need to find out the replacement part number. I contacted Sony but they don`t carry it. The knob is for selecting speakers a and b. Is there a web site that would have a similar knob?

Knob for STR-AV1020

Part Number 4-908-097-21

Part Number 4-908-097-21

Thankyou Biro for the part number. I looked it up on the internet and ordered
it from a part supplier out of Ft. Lauderdale, Fl. Encompass parts distribution