Anybody have experience troubleshooting cassette decks?

[AudiTTFan]

My circa-1995 JVC tape deck/CD player combo had been collecting dust for a little while because I couldn't find one of the speakers. Now that I've got it all set up once again, every tape I've tested sounds horrendously muffled like a 2006 YouTube video. Aside from that, the fast forward/rewind buttons do nothing but pop back out after a few seconds when pressed; anyone know what could be wrong with this thing?

[mariushm]

The most common problem is the rubber bands turning into goo ... you have to replace them.  

You can clean the old rubber bands from the wheels inside with acetone (nail polish remover) ... acetone can also be used to somewhat "refresh" belts that still have some life in them and are just stretched, but replacement belts are so cheap it's often not worth doing that. 

You can clean the heads with a cotton tip something dabbed in isopropyl alcohol or acetone, wipe it with left to right motion.

 

If the desk has some auto stop on fast forward or backwards ... there's some bit that presses down on the tape when a tape is inserted, something with a spring.

When the tape is spooled completely, the tape is stretched/tensioned and that cases the spring to be squeezed and turn off the fast forward. 

if the spring is loose/broken the device may think the tape is tensioned (at the end of the spool) all the time and refuse to do the fast forward or backwards. 

It could also be a belt slipping or a belt being broken in the back 

 

norcal715 did some cassette tape repairs on Youtube, gonna paste some of his videos below... may not be the best cassette tape repairs on his channels, just the first that come in the search results

 

 

 

12voltvids also does good repair videos 

 

 

 

 

[H713]

Basically anything rubber turns to goop. That means belts, pinch rollers, capstans, you name it. Grease also turns to paste over time.

 

Belts can be replaced (usually) without too much hassle. Rollers are often harder, and you might have to resort to being clever. Having a common and desirable machine helps a lot here since there's higher chance that someone makes parts for it.

 

Also, switches might need cleaning at the same time.

 

Tape machines are all prone to the same fundamental issue, be it  a cheap cassette deck or an MTR90.