Sure, R7 is identical with DPC80. You can refer to DPC80's SM.
First step, you'll replace all onboard electrolytic caps, SMT or DIP, all of them; also clean leaking electrolyte from caps.
Second, test reading.
If reading fails again, replace the laser optical head. You can replace the original one by any of following: KSS165/167/220/221, they are compatible.