Need help or service manual for RS COCO mini disk 26-3022...

Hi These are the 1st floppy disks for the COCO made by RS. The units are TEC FB-201. Large full size mounted on their side in silver case with power supply. When dskinit (format) command issued, they go about 35 tracks then an error is reported on the COCO screen. They can't read a disk formatted on a good drive. I checked speed and tried to ajust alignement by moving head stepper motor, could not read to good disk...no improvement These drives use a plastic disc with a "spiral" grove stuck to the stepper motor shaft to step the head along. I have seen this in Apple II drives, it seemed reliable...but I have been told these RS drives were not really realiable... I have two. I would really like to get them going again...I hate keeping stuff in my vintage computer collection that does not work... Thanks for reading Claude