Aiwa CX-NAJ20 Cassette Player Belt Replacement

My neighbor has an Aiwa NDX-AJ20 compact stereo system comprised of the main unit CX-NAJ20 (a CD player, dual cassette decks, and AM/FM radio) and separate speakers. He asked for my help to remove a cassette stuck in the cassette player. The door wouldn’t open on the Playback Deck 1 on the left. He said he never uses the Record/Playback Deck 2. I took the box home and fixed the problem, but join me on an interesting adventure into the workings of this system.

To get each side panel off you need to remove only two screws: the one black screw at the bottom on the side and one silver screw on the rear of the unit. The panels slide back and then down to clear the tabs from their slots.

Here is the view of the open unit showing that easy access to all the internal parts is possible from the right side. On the left side there is a cutout on the large circuit board that allows access to some parts of the cassette mechanism.

With the side panel removed I was able to release the door lock and pop open the door of Playback Deck 1, but there was no cassette inside.

I could see right away that the belts were old and stretched out. See the sagging Deck 2 belt in the picture below. (I had already removed the smaller Deck 1 belt on the other side.)

Loose belts can’t drive the geared mechanism that engages and disengages the cassette transport assembly and locks and unlocks the doors.

It’s a challenge, but you can get the smaller Deck 1 belt installed around the motor pulley without any further disassembly. I didn’t have any new belts yet so I installed a simple small rubber band on Deck 1 to see if that would allow the mechanism to function properly. I put in a cassette and all the functions ran fine even though the output was a bit wobbly due to the uncalibrated rubber band.

An online Aiwa CX-NAJ20 manual provided the part numbers for the belts: 8Z-ZM3-227-010 for Deck 1; 8Z-ZM3-235-010 for Deck 2. I ordered the belts from WestCoastBelts.com.

Inspecting the way the motor was mounted on the tape assembly chassis, the Deck 2 belt goes around one of the posts supporting the motor. More disassembly was required to install the Deck 2 belt.

To remove the tape chassis, disconnect the two connectors on the large circuit board on the side of the unit (see the red arrows in the picture below). This board processes the record/playback signals carried on the gray wires to/from the tape heads. Remove the flat ribbon cable from its connector on the small green circuit board by pulling firmly upward at the blue end (see yellow arrow). The contacts are held by pressure alone. This cable carries the commands from the buttons on the front panel to the tape decks.

Here is a shot with connections to the tape chassis removed.

Now remove the four silver, round-head screws holding the tape chassis to the front panel. (Don’t reconnect the ribbon cable. This is an earlier shot just to show the four screws.)

Here’s a shot of the screw accessible through the cutout on the left side of the unit.

Tilt back the tape assembly chassis to remove it from the front panel.

IMPORTANT:

Do not remove the small green circuit board from the tape assembly chassis!!!

Here’s why:

Under the small green circuit board are two solenoids that activate the white levers and ratchet the mechanism through its sequential modes of operation. The hair-thin wires of the solenoids are soldered to the green circuit board. If you remove the circuit board, you break the wires! Not knowing this, and looking for a way to lift the motor to install the longer Deck 2 belt, I removed the circuit board with the result shown in the picture below. The solenoids are disabled.

The back side of the green circuit board has two pins for each solenoid that mate with holes in the plastic frames holding the solenoids. The wires are soldered to the pins, but unfortunately those holes are for alignment only and not used as electrical contacts. I’ll explain a fix for my error later.

On the other side of the tape assembly chassis are two Phillips screws that hold the motor to the chassis. Remove those screws and remove the motor to install the Deck 2 belt.

Here’s a closeup of the Deck 1 assembly to show the position of the parts and springs.

A top view of the assembly shows the micro-switches for each deck. Deck 1 has a switch to detect the presence of a cassette and another switch to detect the operating mode. Deck 2 has both of those switches and an additional switch to detect the recording protection tab on a cassette case. If the tab is missing, the switch disables the record mode.

To address the broken solenoid wires I was able to extend the wires into the alignment holes on the plastic frame of each solenoid. Very carefully I aligned the pins so they made contact with the wires as I snapped the green circuit board back in place. While not an optimal fix, it allowed me to verify that the tape player was functional.

Additional info: Because of the way that the solenoid wire is wound, it is not possible to unwind the inner winding end. The outer winding end is easy to unwind and get a little more length to insert into an alignment hole. If the inner winding end of one of the solenoids is too short to insert into an alignment hole, it is possible to swap solenoids from one deck to the other. The solenoids snap in and out of a holder on the tape assembly chassis. If the recording function is needed, the reparable solenoid should be in Deck 2. A robust method of repair such as a solder splice to connect the fine solenoid wires to the circuit board contacts is recommended.

The picture below shows the holes in one of the plastic solenoid frames with the wire from the inner winding end inserted into a hole.

In the picture above you can see a ring magnet attached to a spindle (just below the large white pulley). There is one for each deck. A Hall Effect sensor EW732 is mounted on the green circuit board to sense the change in polarity of the ring magnet as it rotates when the cassette tape is playing. This is a clever counter for the tape player.

The picture below shows the installed location of the door latch. Note the position of the spring in the slot at the bottom so the door can be pushed open.

The latch can be moved out of position when not secured by the screw holding the tape assembly chassis in place.

Here’s the latch removed. It is easily popped back in place.

After both belts were replaced I simply buttoned the unit back up and delivered it to my neighbor who inserted a cassette of Oscar Peterson that we listened to sans wobble. Hopefully he will get many more years of enjoyable music out of this Aiwa system.