Disk System: Error 21, 22 and 27 with one game

[Técé]

Hello, until 2022 I was the proud owner of an FDS with its original belt in good condition! But in 2022, the inevitable happened, and I had to change the belt. So, for reasons that would be long and tedious to explain, I wasn't able to make the repair until yesterday, June 12, 2024.

So yesterday and today, I repaired my FDS, with a new belt, of course. After testing (I own two games, a volleyball game and Super Mario Bros. 2), unsurprisingly, I got the famous error 22, because the read head had to be calibrated.

So I calibrated the playback head, and after many unsuccessful attempts, I finally succeeded, and the volleyball game finally works! But, and this is the weird thing, Super Mario Bros. 2 keeps making error 22! It even alternates with error 21, and more rarely, error 27. This is astonishing, because before my FDS failed in 2022, my SMB2 had never failed me, so I don't think the problem lies with the game diskette.

That's why I've come here, in desperation. I've come looking for help to try and find out where the problem with my FDS is coming from.

Best regards,
Técé

[Skawo]

Which method did you use to calibrate the spindle?

[Técé]

I used the method of turning the white toothed wheel towards the belt until the tiny black circle was aligned with one of the reliefs on the metal triangle, after which I loosened the small black screw on the axle with an allen key, to reposition the axle facing the disk slot, then tightened the small black screw again.

After doing this, the volleyball game worked, but not Mario 2.

[Skawo]

Yeah, that particular video makes very dubious claims, sorry. That trick only works occasionally, and you probably got it *close enough* for Volleyball to work, but not enough for Mario 2.

See the spindle hub alignment section here:
https://www.famicomdisksystem.com/tutorials/fds-repair-mod/belt-replacement-adjustment/

[Técé]

You were right, I had to make several readjustments, again and again and again, and by dint of insistence (sometimes with the belt coming off, forcing me to put it back on), I finally got everything working!

Thanks a lot! You helped me find the right solution!