I assume you used the laser replacement thread, I'm glad it's still serving people as a good reference. I still have to update it with the Duo-R Photos.
Once the laser itself goes bad there's really no "fixing" it. I disassembled one to try and revive it many years back, but the pickup was just completely worn out, and unless you want to keep that tiny piece of plastic around for nostalgia, or perhaps as a "parts" unit, it serves no function. Electronix Corp used to sell the Japanese HOP-M3 lasers for about $6 more than the current Chiinese/Hong Kong-Made (they work great) lasers that you can get for $14 on alibaba. It usually comes down to the laser itself, as opposed to jumping right into a trim pot adjustment. I only recommend that if you have installed a new laser, and notice:
1. Severe lag time
2. No Response
3. Read issues, displaced sound issues, etc
It is possible to "tune" the laser via the trip pots as described in the thread, but I would only recommend doing this if you have an ocilloscope, some electrical knowledge, and a lot of patience.
All in all, its not worth fixing, you'd have to find the laser-pickup part and that is getting way too meta. just buy a new one, and have a spare in case it ever goes bad. It will be the $28 insurance policy for your Duo.
caw