I just obtained a decent condition WM-7. I must say that it is a rather well over engineered mechanical wonder.
Cosmetically nearly perfect. The window was a bit fuzzy but some tamiya polishing compound fixed that. Replaced belt and pinch rollers.
Other than that it needs new caps (low audio levels, audio hum/buzz AGAIN), and I seemingly have a mechanical problem with the FWD gear part no. 311. (The green arrow gear.)
As you can see, when playback mode is engaged, the green gear is supposed to hit the red gear, mesh together and drive the reels.
Unfortunately, I believe the green ones have shrunk. Not only are they both a little tight, The one on the left barely meshes together (it often pops out and grinds), but the right one is ok unless a tape is in.
As there is no way for me to obtain new gears (unless by some miracle I come across spares locally), I have 2 options:
1. Attempt to cast a new gear, the mold will make it slightly larger.
2. Adapt the rest of the mechanism to fit the new tolerances. I have already actually ground down part of the limiter for the more severe left gear, and it has improved it to the point of being usable. However, it is slightly more noisy now. I will prefer to reproduce the original size gear and revert the modification back.
Anybody encounter similar problems with the WM-7? And does anybody know any method of casting and reproducing a new gear?
By luck I managed to find a similar gear in a shop! However it had to be ground down to fit.
The new black gears turned out to be a nearly perfect fit, working much better than the slightly shrunk originals.
After solving a bunch of other random problems (disintegrated volume pot, dirty switch contacts, seized up servo, rotten pinch rollers)
this once junk condition unit now sounds great.
