Relubricating gears on MD portable units

This will be a physical repair guide, focusing on getting a cranky MD mechanism back to proper working order!

Here are some symptoms that this will (likely) fix, or at the very least, make for a better experience.

• Very loud seeking noise
• Stuttering audio, or constant pauses during playback
• Slow track changes, or long pauses between tracks (may or may not exhibit with any of the above)

• A space to work; preferably with ESD-safe materials, or a large, flat piece of cardboard (Amazon boxes can work for this)
• Set of small screwdrivers; I prefer and recommend an iFixit toolkit, but something like hobby screwdrivers or eyeglass repair kits should have bits small enough for this
• Small tweezers; these should be ESD-safe, but common tweezers (for eyebrows/splinters/etc) should also work
• At least one small container; this is to hold the screws so they aren't lost
• White lithium grease. This must be white lithium grease; not a spray, but actual grease.
  • Molykote EM-30L is the “proper stuff”. Usually you can get a small 5-10g tub on eBay for less than 5 £/$/Eur etc
• Isopropanol/Rubbing Alcohol; 70% or higher, this is for cleaning.
• Q-tips/cotton buds; these are for removing old grease and general cleanup while you're in there
• Soft bristle toothbrush; same as above, mostly for the old grease, as it's very tedious to do this part with q-tips
• TIME. This is a simple procedure, but it can get tedious. Please make sure to set aside enough time to get this done in one session, if possible.

In this example, I am using an MZ-N920 that I have previously serviced. This is very similar internally as the MZ-N910, and so, mostly applies to that unit as well. Shown here are all the things listed above (excluding the camera and setup taking these photos!).

On the N920, there are 5 (five) screws holding the bottom case onto its internal frame. You want to unscrew those and put them aside for later. Next, you want to open the gumstick battery door straight out, and then pull the plastic part straight off. This may take some force, and it may also break the plastic bits in the door. You can take the case off without this step, but it is far easier to remove the door, than to navigate the case bottom around it.

In my case, this did not damage the door or the contact.

Next, with the screws (and battery door) removed, we want to look at the side with the door.

On this particular unit, the audio in/out, and USB are on the left side, while there is nothing really on the right. So we want to pry gently on the right, to angle the case off the important stuff on the left. Like so:

Once you get to a certain point (this is different for every unit), the case will just….fall off for lack of a better term. You are now inside your unit.

Put the bottom case aside, we are done with it for the moment.

Here come the tricky parts, and I unfortunately don't have any photos of this. But you need to unlatch (carefully) three ribbon cables. Then remove 3-5 screws from the mainboard. And then be careful lifting the board out, as the record head is soldered in this unit.

Flip the board over, as shown.

From here, you can dab little bits of the lithium grease onto the worm gear, and work it back and forth manually. You can do this with a q-top, toothpick, or tweezers on either of the two radial gears shown here. If there is old grease, you can clean it up now, and then reapply.

After that, reassemble the device (the ribbon next to the battery bay is very tricky) in reverse order. Once closed back up, but before screwing the casing back on (or without the casing, but with the small screws on the mainboard) you can test out how it works now.