How do I fix, and is it worth it, to repair the cassette mechanism I think on Zenith MC 6190. Machine is otherwise pristine. Purchased new back in the day...

The weakened belts in the deck combined with harden dried out grease will not allow the mechanism to cycle. That is why I steer people away from dual cassette decks as they can be very expensive to fix costing more than the original price. I have been doing these for near 45 years. What model are we talking about here?

You need to take the cover off and look inside to see if there is something inside that should not be. Perhaps you can look with a flashlight through the entrance hole. You could pick up the machine and shake it and see if anything is rattling around. These things have many plastic and nylon parts which can break over time and the machine will sense a problem and eject. If you cannot find a problem by the suggestions above then it will need to go for repair-unfortunately it would probably cost more than it is worth to have it repaired.

The mechanism needs new belts and maybe grease cleaning and new applied. The dual cassette decks are not usually worth the charges a Technician will charge to fix them.

The belts you have replaced are used to operate the loading/unloading mechanism I assume. On the bottom of the cassette mechanism you will find the other belts...one from motor to idler wheel assy. or actual reel hub. Older cassette decks also used a belt to drive the tape counter mechanism.

A good place to see what machines are selling for is Ebay. That's where I sold a sewing machine and an embroidery machine.

It helps to know your product and machine embroidery lingo.

What are cassettes? Floppy disks? These make the machine borderline obsolete.

Memory cards are still around, but most EM now have USB connectivity or USB flash drives.

Satin thread? Embroidery machines use Rayon or Polyester embroidery thread.

Having had the machine recently serviced is also a plus.

i found a website that explained what was wrong and how to fix.

I'd get the lamp replaced for sure. If it has a ballast - change that at the same time. However, a Zenith repair center should be able to tell you whether it's worth doing or not.

Mexican captions

This sounds like a dirty or sticky pinch roller - use a commercial cassette head cleaner - or ear but with a alcohol cleaner -

If the capston is not rolling the cassette forward this my be due to a broken belt - or may have just jumped off - power down the product and disconnet from the mains - then open it up - normaly the front come away undo the mounting screws from around the cassette mechanism normaly around 4 and carefuly look at the back there should normaly be 2 rubber band one to the capston and 1 to the pich roller the belt that may be broken is the smaller of the too. most cassette deck use the same size belt