When I started looking for a MiniDisc desk for home usage (i.e. NOT a portable) that I could hook up to an existing receiver/speaker setup, I started at Buyee (of course) and found this Sony MDS-S30. It was in great shape, was only $21 USD (Feb 2023 rates) and was confirmed to "power on" but they didn't say that playback worked...
You would think that someone could just put a MD inside to test, but oh well...
When it arrived, I was pleased with the condition since it was nearly perfect and was also a nice, compact form-factor. Unfortunately, that was as far as I got. I wasn't able to insert a MiniDisc! =(
Inserting a disc would work about 80% of the way, then after being grabbed by some internal mechanism, it would just get stuck with the label end sticking out and you could hear a whirring/spinning noise. I had to forcefully pull the disc out to remove it.
Note - I've also contributed to the minidisc.wiki!
Well, time to open it up!
Just a few screws on the side and one at the back and the top cover was off. Very easy.
Now I didn't spot anything obvious right away and I hadn't worked inside an old 90's appliance well... since the 90s?
I decided to plug it in to see what it was doing.
PLEASE BE CAREFUL WHEN WORKING ON ELECTRONICS THAT ARE PLUGGED IN.
After inserting a disc, I could see what was happening. The mechanism wanted to take the disc in, but there were two pulleys spinning around uselessly because the belt was broken!
See red arrows - these are the two pulleys required to pull the MiniDisc in.
To clarify even further as I got closer, the belt had melted/deteriorated into a black, gooey, sticky mess...
I scraped off what I could and got some alcohol wipes as well to get in there a bit more. It wasn't 100% clean, but good enough, I think.
To confirm that was the culprit (yes, pretty obvious), I had to connect the pulleys, but I didn't have any spare belts on me...
What's a tinkerer to do? Well, I grabbed one of my daughter's ponytail rubber bands, that was just about 2.0 cm in diameter.
A bit of tweezing got it into place onto both pulleys with just enough tension (you don't want a belt that's too loose nor too tight).
I found the easiest way was to loop the rubber band around the smaller, inside pulley, then stretch it using tweezers towards the outside one. I did it multiple times, snaking under the metal cover. Of course, it would be trivial by removing the metal cover, but I wanted to do something quickly.
Let's test that disc again...
Sure enough - it worked! I laughed as my daughter's orange rubber band allowed the pulleys to move the mechanism to pull the disc inside.
After buttoning it all up and testing the features, I now had a fully-functional MD player/recorder deck that was well-discounted because it was sold as "unconfirmed".
Of course, I couldn't leave my daughter's rubber band in place, so I went off to Amazon to order various belts in different sizes, hoping one would fit perfectly. At this point I hadn't researched exactly which band type (flat, square, round) nor size to buy but there were some "variety" packs on sale.
I received the belts a few days later and found one that fit correctly!
In the official service manual, this entire mechanism is the MDM-2 (there are different generations of MiniDisc mechanisms) and this belt's part # is 4-967-656-01. I initially replaced this with a small flat belt which was too wide and would slip off after 20-30 times so I've gone with a square belt that fits the grooves better and that's still going strong. Ideally, I'll get the "official" belt, but it's working fine with no issues at the moment.