Hello, I while ago I made a video on YouTube about the center gear. Someone comment this on the video: The centre-gear (which includes the slipper-clutch) on the DD's would split because of the shock load delivered at the end of the tape on FF/RWD (no real auto-stop, the servo just cuts power to the now jammed motor/capstan/flywheel after a second or so). I sold the DD33 I bought new in 1992 in 2020 (which must have seen 1000's of hours of use) and the centre gear was still fine because I ALWAYS, from day-one, either watched or listened for the 'leader' tape to appear and hit STOP before the the tape slammed to a halt (needs decent reflexes). For broken ones, I've often wondered if, after removing the plastic outer from the steel disc it's moulded around (easy as it's already split), the disc could then be turned down to a fractionally smaller diameter and the plastic outer re-bonded to it with the broken ends carefully dressed (minus one tooth) to reform a perfect gear. I find this a very interesting theory and I have to say it makes sense, what do you think?
The theory certainly does make sense (however to me it remains a theory), especially when comparing to the WM-EX walkmans situation where there are indeed some with intact clutch gear as of 2022. However, the EX gear is of a different design, so I would not draw any generic conclusion based on that alone. In the EX design, the gear actually has some room to shirnk, it's not as tight of a fit. Broken POM gears that were molded onto metal discs/shafts are a common problem in many walkmans, cassette players/recorders, even on some Hi8 VCRs. It's certainly far from being unique to DD walkmans. One example in regard to shrinking is the recently posted SONY M-1000 microcassette recorder that I repaired. Unit has sat unused for many many years and gear is split with a huge crack. https://stereo2go.com/forums/threads/sony-m-1000-micro-cassette-recorder-repair.8094/#post-61216 Now, there are some things that are clear and can be found online: POM does shrink after it's injection molded until it cools down. Shrinkage can continue even several days after part has been taken out of the mold. This alone will put the POM part under significant tension alone, even if NO further shrinkage will occur over the years. However the question is if there is really no further shirnkage, which can be caused by exposing the device to heat, by the passing of time or both. Then Sony (and other manufacturers, as it's not just a Sony problem) would know about this shock situation when designing the mechanism. Mechanism should be made to work regardless of how one uses FF/REW, otherwise you'll have just a lot of warranty problems which you don't want as a company. Another aspect that I can think of is if breaking of gear was to be caused by shock, it would have happened a lot earlier in the life cycle of the product, maybe even during the warranty period. Unfortunately we have no data to confirm if that was the case or not. The theory itself is certainly interesting, but I think we need a lot more data until we can draw clear conclusions. As for me, even if I would see an intact gear I would choose to still replace it to avoid breaking in the future and the need to repair device again.
The 80's saw an explosion in different plastics, unfortunately some didn't stand the test of time. Now a days they seem to have perfected them but it's too late for the portables. As a side note, I used to do sales in plastics, we had a vault with some of the special blends, stuff like Ultem that went for silly money had to be locked up. The expensive plastics had very high heat ratings or abrasive additives which wore down the molds quickly. I've posted some articles from a Japanese Plastics Magazine in the archeology threads, the magazine is on archive.org if anybody is interested.
