User:Mjb/Nakamichi CR-3A cassette deck restoration

I let my Nakamichi CR-3A cassette deck sit unused from 1999 to 2017. After sitting for that long:

• upon inserting a tape with the power on, the reels were barely able to do the usual quick mini-wind to adjust the tension
• the fast-forward and rewind buttons were completely inoperative
• the play button would result in no reel motion, but one of the capstans turned for a couple seconds
• the play button only sometimes resulted in no engagement of the heads, which would not disengage until after a power cycle

There were 2 main problems:

• The cam motor had developed a dead spot, meaning it is just sticking and not turning freely – this prevents the heads from moving into position when play is pressed.
• The capstan belt was now too stretched-out and loose to reliably turn both capstans – this apparently prevented the reel motor from operating as well.

This all should also apply equally to the CR-4.

To remove the transport mechanism:

1. Unplug the unit and press the power button a couple times to make sure there is no risk of electrical shock.
2. Remove the cassette door (mine had been removed and lost years ago, so I didn't have to do this).
3. Remove the lid (2 screws on each side, one on the back).
4. Remove the screws holding the transport onto the front of the unit (3 screws on top, 2 on bottom)
5. Remove the screw which holds the black ground wire to the back of the mechanism.
6. Carefully clip and discard all of the cable ties on the wiring leading from the circuit boards to the back of the mechanism.
7. The whole mechanism should now be free to slide out. It slides backwards (further into the case). You might have to lift up a little on the front molding to give it more room, and you will definitely have to tilt the mechanism forward as you pull it up and out. You won't get it very far, though, because the wiring is so short.

If you want to get it all the way out:

1. Using tape you can write on, wrap and label each set of wires with the appropriate connector ID on the circuit board.
2. Using an IC puller or needle-nose pliers, carefully pull the wiring connectors out of the circuit board. Don't grab the wires.

You really don't need to take it all the way out. You still must clip the cable ties but you can leave the wiring connectors attached and it will make it easier to test, if a bit awkward. While testing, I left the ground wire detached since it is so short, but kept everything else attached.

As you are doing all this, you will probably hit the door latch a few times. Don't worry about it, just push the door back closed.

To service the transport mechanism, here is what I did:

• Spray electronic parts cleaner wherever you can find a hole in the 3 motors The cam motor is the sideways one near the copper tabs. The reel motor is in the middle on top. The capstan motor is the big one that juts out the most. I did not really have to do anything to the reel motor.
• Plug in the deck and turn on the power.
• The capstans are the metal rods that poke into the holes at the bottom of the cassette, and the flywheels are the big metal discs that the rods are attached to at the back of the mechanism. The flywheels are turned by the belt which is attached to the capstan motor. They should both turn at the same time and at the same speed.
• With the wiring attached, insert a tape and keep pressing play and watch the capstan flywheels to see if the belt turns them. If one or both are slipping, manually give them a push with a clean, dry fingertip. When I did this, so that both wheels were turning, the tape played, but the motor just did not have any "oomph" and would quickly slow down and quickly peter out. Clearly the belt was slipping.
• While doing the above, with a soft tool (cotton swab, pencil eraser, toothpick), try to jiggle the white plastic gears attached to the spindle of the cam motor, to give it a little help getting past its dead spot. After the parts cleaner did its magic and after several times of pressing play and using my finger to help the capstan flywheels turn, everything seemed to be working, including forward and rewind.
• Remove the metal plate from the back of the transport so you can get the belt off and pull the capstan flywheels out. There are two obvious screws on each side, and two more on the side, close together, near the door latch.
• The flywheels pull right out. Be careful not to disturb or lose the little copper pieces that they rest on.
• Clean the capstan rods so the tips are shiny again. I used ultra-fine sandpaper. Put a drop of general-purpose lubricating oil down the shafts that the capstan rods go into. Replace the capstan flywheels.
• I temporarily replaced the capstan belt with a rubber band and put the back cover on. Everything worked now without any finger help. A cheap rubber band is not a good substitute for a real belt, though. The choice is a reproduction belt for $40 plus shipping from Marrs Communications Inc., or a compatible "close enough" belt for $6, shipping included, from AdamsRadio.com. I chose the cheaper option. It is a PRB brand belt, model # FRW 9.7, which is not an exact match but is the closest you can get. It is maybe a millimeter wider than the old belt, but just about the same thickness. Does it produce the same wow & flutter as an authentic belt? Who knows. It is tolerable, but I have no way of measuring what it actually is nor do I know how it compares to the authentic belt.

Speed adjustment was needed once I put everything back together screwed the transport back into its original position in the case. So before putting the lid back on, I worked on that.

Since I don't have a calibration tape (e.g. one recorded at exactly 1 7/8" inches per second and containing a sine wave at a known frequency), I had to resort to other means. I played a commercial tape of music which I also have on CD from the same era. This assumes that both were mastered from the same source with no speed variations. I used a tiny flathead screwdriver to turn the pot hidden inside the back of the capstan motor to adjust the speed. As is typical with these pots, it is impossible to fine-tune them, they have a lot of play, and they speed up when you are trying to adjust them, so you have to adjust a little, take the screwdriver out and check it, adjust a little more, over and over until you get the speed as close as you can get it to perfect, keeping in mind that perfection is elusive. Also keep in mind that many of your homemade tapes may well have been recorded at speeds that are way off. I have some tapes that were recorded about 3.5% too fast, so they play slow by that much now.

In the old days I would play the CD at the same time as the tape and try to sync them up, DJ-style, using the speed control. Now I just record them in Audition and zoom in on the spectrogram, adjusting the speed so as to try to make some "bright horizontal line" sustained tones from the tape be at the exact same vertical positions as their counterparts in the CD rip's spectrogram. The spectrogram view has to be at maximum vertical resolution (65536) which means sacrificing horizontal (time) resolution and having slow rendering, so it's not ideal, but after about half an hour of futzing around, I got the speed to be really close to a match for the CD, so it's good enough for me.