(1) Remove the back cover, note the locations of all tethered wires, disconnect them.
(2) Remove all the knobs
(3) Disconnect the speaker connectors.
(4) Remove the chassis from the front case. Note the location of all screws. If any wires remain tethered, note their locations and disconnect them.
(5) Carefully remove the tuner dial -- set it aside and protect from scratches
(6) Remove the screws securing the mechanical assembly.
(7) Carefully lift out the mechanical assembly -- carefully turn it around. It is tethered with wires. They are soldered and not easily disconnected. It is easier to work with the assembly desoldered and removed but is more work. It can be rebelted tethered but you'll need to be careful not to fatigue any wires and snap them. Because if you do, it will be hard to find where they were originally connected to.
(8) Place a cloth or other protective material between the mechanical assembly and the chassis in such a manner that you can work on it without scratching or damaging any cosmetic parts.
(9) Remove the backing plate that secures the flywheel. This should expose the flywheel and rotating assemblies.
(10) There is a main belt that is hidden under the flywheel. It is a 5.4" Large square belt and not normally visible. Lift off the flywheel but be advised that a small washer will fall from the capstan needle from the front side. Find and keep this washer -- you will need to replace it when done.
(11) If you suspect that the clutch is worn (slipping), then the clutch will need to be removed, cleaned, and the friction surfaces slightly abraded to improve friction (there are no replacements).
(12) Clean all belt and pulley surfaces with 100% (or as near as possible) isopropyl alcohol.
(13) There is at least 2 belt routing methods so the one you employ will depend upon your boombox. Best for you to note the original routing.
(14) Replace all belts with proper sized belts. A belt installation hook tool is almost required to do the inner belt.
(15) Reassemble, reversing the entire process.
This is a simplified description of the process. You must exercise common sense and possess good mechanical aptitude to do this. Not every step is enumerated here. You will need to note and document along the way as necessary in such a manner as to allow you to reassemble. Please don't take short cuts because then you'll be back asking where does this wire go, or what screw goes where and such. The best reference that you're going to have are the photos you took of the process to guide you back to the beginning. Think of them as bread crumbs.
Tips:
(1) Lube the capstan needle shaft near the base with a teeny bit of silicone grease. Also slightly lube the flywheel rear shaft to nylon bushing on the backing plate.
(2) It is easy to get grease on the belts when slipping them on since they are likely to contact one of the greased locations. Make sure you go over everything when done with 100% isopropyl alcohol to remove any trace of grease or you'll just spread the grease over the entire pulley assembly and A: cause belts to deteriorate faster and B: cause potential slippage.
(3) The flywheel backing plate might include a freeplay adjustment screw (it would have a spring). If you did not count the turns to begin with to restore to original spot, adjust to remove freeplay but allow fre movement of flywheel. It should spin like a bike wheel. Too tight and it will affect playback speed.
(4) If it continues to slip or eat tapes -- suspect a slipping clutch.
(5) There is a tendency to overgrease parts. If parts that originally slid freely are greased, the part may not function properly when the grease gets old and thickens up preventing free movement of that part.
And if worse comes to worse, and you feel like you can't do this on your own -- send it to me and I'll replace them for you for a few $$'s.
