Sony DD auto-stop

I wonder how the auto stop is supposed to work on Sony DD walkmans. After replacing the center gear, and reassembling, I am not quite sure I got it right. This is how it works on my walkman if I reach the end of the tape:

* In FF: motor stops, battery light goes off
* In RW: motor stops, battery light goes off
* In PLAY: motor keeps running, battery light is on. Motor will keep running until batteries are completely discharged.

When inspecting what is happening in PLAY mode, I can see that the lower part of center gear is rotating, but the gear with the magnet is still. That is, the magnetic clutch is "slipping".

I don't think this is quite right, but what is the correct behavior?

 

I forget to mention, that in neither case does the player go back to STOP, i e pop back the pressed button.

 

hi，Dag
I would say that you ask a good question and I known what’s your problem .
In play mode,when it stops, the correct behavior is :the play button pops up, motor stops,battery light goes off.
In your case, I think you didn’t get ‘ the black thing’ in the right position ,that would cause your problem.
the right position of the ‘black thing’ is shown as this photo .
Please check yours.
The automatic stop function is one of the most clever designs by Sony engineers and I will explain how it works later

 

Thanks Dave, great response! Now I know what to look for. I was aware that I should align that, but maybe I missed it in the last minute. I will check this the next time I open it up.

So, the stop button should not pop up when in FF/REW and the end of the tape is reached? If I understand correctly, the motor should just stop, but the FF/REW button should still be down.

 

Unfortunately, that was not the problem. The black lever is aligned as is shown in the picture, but it still doesn't work. When the take-up real is blocked, i can see a small white lever is moving, but it never activates the stop mechanism. if i manually pull the white lever a bit further, the auto-stop is engaged. I have another DD device for parts, but this one shows the same problem. But it will work once in a while on that device.

When looking at the mechanism under the center gear, i don't see anything that is obviously wrong.

 

Since the black lever is in the right position, there is another possibility that would cause the problem.
Check if the big center gear assembly is a bit ‘too high’.
if it is too high, the black little gear could not reach the white gear, these tow gears are shown in this picture.


The automatic stop function works like this:
When in play mode, the big center gear and the magnetic gear are all rotating, when the tape reaches the end, the magnetic gear stop, but the big center gear is still running, the gear levers under the big center gear detect that the magnetic gear is not running any more,and the plastic lever will then push the steel lever and pop up the play button.
I don’t know if I make it clear enough

 

Look carefully at these pictures and understand how it works.

 

With the help of your pictures and explanation, i think i understand what is happening. Thanks!

The little black gear under the big center gear is turning the white gear, that part is working fine. But it seams that when the teeth of the black plastic part should engage with the little black gear, it starts slipping. So here, I am talking about the black part that is not actually a round gear, rather it has one toothed edge.

If i press slightly on top of the center gear while turning it, I can get the black part to engage with the little black gear, and activate the auto-stop mechanism. I hope you understand my somewhat unclear description.

The question is then what to do about it. If the center gear is riding too hight, is there a way to get it a little lower? Worse case is that there are damaged gears/tooths. Should I move, or turn he little black gear around to make them engage?

 

According to your description ,it seems that the little black gear under the big center gear doesn’t drive the white gear well, the whole big center gear assembly is a little too high,you can bend the iron arm a little to low down the whole big center gear assembly.be careful,just bend a little,not too much !

 

Aha, simply bending the metal arm down, that sounds easy enough. Will try it tomorrow!

 

Very annoying! As can be seen next to my fat finger on the image, the first tooth of the little black plastic part that should engage with the black gear under the big center gear is missing. I opened up my other walkman for spares, but it had exactly the same issue. This is the explanation why the auto-stop doesn't work.

 

there are four teeth on that black part ,if the teeth is missing or broken,it won’t work.
it seems like you are too rude to it.
When installing the big center gear, you should take care of it and avoid damaging it.

 

I have three teeth on both specimens. I don't see how I would have damaged them. Maybe if like you say the center gear was a little too high, and that allowed slipping against the teeth rather than engaging fully, causing the damage. Or maybe the material has weakened over the years.

Anyway, looks like I am out of luck, unless someone has the part to sell

 

Just to give an update: I put everything carefully together, and lo and behold, auto stop works! So even without 1 of the 4 teeth it is now working. Maybe it helped to bend down the center gear arm as you suggested.

Thanks a lot for you insights!