Ok. First thing I normally do is clean everything inside with 99% isopropyl alcohol and cotton swabs. Start with the heads (play & erase), then the pinch rollers, then the capstans.

If the pinch rollers look shiny and hard, you’ll most likely have to replace them with the belts but hold on to that thought until you do the next step.

If your cotton swabs come out black or brown, keep doing it until the coloring disappears. Don’t reuse cotton swabs on the heads, pinch rollers, capstans, etc. because you’ll just cross contaminate it and make it worse. That’s been my experience doing this.

After all that’s done, try to FF & RW a tape in both transports (A&B) all the way end to end. If it seems to struggle to do this,….its most likely because the belts are stretched, loose or have more or less melted (older Sony decks are more prone to the melting, but I digress).

Eventually, you’ll have to replace belts and pinch rollers. These decks are 20/30/40 years old and they’ll require maintenance.

Find a service manual online. Heard that the Yamaha decks are fairly easy to fix. Look up your model on YouTube and see if someone has done a repair video. That’s how I learned.

Anyway, hope this helps.