Help repairing disk drives

[doragasu]

I have two CPC6128 units, and both have a broken 3" disc drive since I got them. I decided it's time to try fixing them, but I am not having success so far. As usual, both had a broken drive belt. So I 3D printed the belts using FilaFlex (an elastic material), installed them and now the disks spin apparently properly. But whey I try reading a disc, both drives show the "disc missing" error, although with different behavior:
- The first one (mounted in an older CPC model) when commanded to read the disc, spins it a little bit (not even half a turn I would say) and then shows the disc missing error. Each time I retry, the same happens: it spins a bit, stops and the error is shown. Upon closer inspection I noticed the pin that pushes SW1 is missing (I suppose the previous owner disassembled the drive and lost it). So I tried soldering a switch in parallel to SW1 so I can close and open it at will. If I try closing the switch, when I try reading the disc, it does not spin, not even the little bit like it does when the switch is open. The LED in this drive is always on, but with a very low intensity. When I try reading the disc, it lights a bit more for a split second.

- The second drive (mounted in a newer CPC model) when commanded to read the disc, starts spinning the drive, then shows the disc missing error, but the disc does not stop spinning until I select Cancel option. I noticed with a multimeter that when I press SW1, the contact does not close, so since it seems this switch might be damaged, I repeated what I did in the other drive and soldered a switch in parallel. But in this drive it does not matter how the switch is configured, the behavior does not change. The LED in this drive is always off, even whey it spins the disc a bit.

I measured the voltage arriving to the drive, and the 5V is a bit low (4.78 V), but since the computer is running perfect, I suppose the problem is not here. The 12V rail measures 11.8 V, so I suppose it is OK.
What else can I try, any suggestions? I am afraid maybe one or both of the logic boards might be damaged, because of the very different behavior of both drives...

[vasilisk]

Before installing the new belt, did you completely clean the remains of the old one? I am not familiar if the 3d printed belt has the same characteristics with the original one.
You say "spin apparently properly" but you can't know if it spins with the correct speed.

[gerald]

1st, leave that switch alone, it just here to detect if the disk is write protected or not. 

Now, on the second drive, it is expected that the drive spin until you select cancel. That how its supposed to work.
So the 1st drive clearly have a problem spinning the disk. 

On both drive, double check that you properly clean all remains of the old belt.
Any remaining bit and this will locally modify the actual rotation speed and make reading impossible.

Also, you better get a real belt rather than using printed one. I am no 100% sure that they are smooth enough.

[doragasu]

Thanks for replies. I will give a thorough clean to the drive (even though I think it was OK). I can also search for a "proper" belt.
Here is a small video of how the 3D printed one goes. Maybe it can help diagnose if the speed is correct:

https://www.youtube.com/watch?v=hwdDZVha5nc