Sansui receiver takes more than five minutes to...

Question

Hi Sir,
My 30-year old Sansui receiver model G7500 takes more than five minutes to turn on the green ligh, when the green light turns on everything is fine. When the green light is on, I turn it off and turn it on, it takes only few seconds.
Would you suggest me what cause this problem and how to fix and what parts should be replaced.

Thank you vere much
HUY LAM