Help fixing SL-Q3 size selector failure

[brewera]

I have a few Technics SL-Q3 turntables that I have been going through and cleaning up the old grease and re-capping. I have one where the size selector is just not working. It always wants to go to the 7" size. The good thing is that I have another SL-Q3 that works just fine and decided to do some side-by-side videos to see if you all can help me isolate the size selector issue. From what I understand looking at the schematics the key parts that control the automatic placement of the stylus in the size selector area are the metal chord connected to the index plate which is associated to the operating plate assembly.

I was able to take some videos of the working turntable vs the NON-working turntable and am looking for some suggestions. I am unsure if it is just a worn out spring on the operating plate assembly as I tried swapping springs between the two and while the selector works in 12" and 10" size now if I set the selector to 7" the stylus gets near the 7" dropping point and then starts moving quickly toward the center of the record. Anyway, any insight would be super appreciated!

SL-Q3 WORKING size selector (filming through dust cover with actual record on turntable)

SL-Q3 NON-working size selector (filming through dust cover with actual record on turntable)

Manually moving working SL-Q3 size selector

Manually moving NON-working SL-Q3 size selector

 

[brewera]

Here are the other two small vids of the spring action of the working vs the non-working. Cheers!

Spring action of working SL-Q3 size selector

Spring action of NON-working SL-Q3 size selector

 

[brewera]

Well I guess gathering data and writing out the post brought clarity to the problem. I decided to short the spring in the picture below and that was the solution. The spring was just stretched out from age. Hope this helps anyone else.

 

[Soulrevolver]

Thank you @brewera for very informative videos! I had exactly the same problem: size selector was forced back to 12" from 7" or 10". I was able to wash the Operating Plate Assy with isopropanol without disassembling the whole automatic mechanism, gave it a good new lithium grease but it didn't still work.

With your videos I could observe the proper functioning of the assembly and noticed the plastic pin should slide in the hole/slot here. In my case, the washer holding the plastic part was completely stuck to the metal part. With a sharp thin knife I was able to detach the washer from the metal part, gave it a good grease and now it's as good as new!

Thank you, I think I wouldn't be able to figure it out without your videos!