Nakamichi BX-100/BX-125/BX-150 cam motor repair


An article from Pieter's Knowledge Base



Introduction

As of the BX series of cassette decks, many Nakamichi decks have been fitted with a mechanism manufactured by Sankyo. It can be found in the BX, CR, DR, 'Cassette Deck', ZX, and MR series (but not all models of those series). The cam motor is responsible bringing the heads into position, as well as some other operations.

A well known issue with these Sankyo mechanisms, is that the so called CAM motor (aka control motor) stops working after a while, especially when the deck is not used for a longer period. The so called carbon brushes inside the motor get oxidized and no longer make proper contact with the so-called commutator of the rotor (the part of the motor that spins around). The result is that the deck will no longer go into play, pauze or record modes, or if it does, will not return to stop mode. However, the deck will often be able to wind the tape forwards or backwards.

When this happens to your deck, the best thing to do is to replace the motor with a new one. Unfortunately, these motors are no longer available, and it's difficult to get a substiture that is easy to fit inside your deck. The best next thing is to clean the motor. Elsewhere on the internet you can find instructions that basically boil down to spraying some contact cleaner (e.g. Deoxit) into the motor. This will work for a little while, but at some stage, the problems will return.

I have developed a procedure that will make the cam motor last longer. It involves opening the motor itself and cleaning it thoroughly. Below I will show you how to do it. The instructions are based on the BX-125E deck, and also apply without significant changes to the BX-100 and BX-150 (as well as their European E-versions). Other models in the BX series are probably very similar as well. With other series probably other steps need to be taken to remove the mechanism form the cabinet (it actually might not be required at all), or to take the mechanism apart, and the cam motor might actually be in a different spot. Please search the internet for instructions applicable to your own deck, or consult a service manual.

Update: the procedure I describe below does not always produce long lasting results. I therefore strongly recommend that a new motor is fitted. I personally use the RF310-TA11400 motor, but there has been some discussion on forums that this is not a good motor. I personally think it is good enough, but some repair professionals disagree with me. I can at this time not recommend another motor from my own experience. Please search the internet for a solution that meets your demands.


Warnings and disclaimers

  • These instructions are meant for repair professionals and experienced electronics hobbyists. If you have never repaired electronic/audio equipment before, than this procedure is probably not for you.
  • When you carry out the instructions below, you do so at your own risk. I will not be held liable for any damages that occur when you try to repair your own deck.
  • Be sure to disconnect your deck from mains power, as there are parts inside that are high voltage and could result in dangerous electric shocks.
  • Take your time, don't rush or force anything. If you do, something will likely get broken, possibly even beyond repair.
  • Read all of the instructions below carefully before starting to work on your own deck.

Required tools

You will need some tools in order to get the job done:

  • Q-tips for cleaning purposes
  • Big Phillips screw driver (A) (to open cabinet)
  • Medium size Phillips screw driver (B) (for most screws).
  • Tiny Phillips screw driver (C) (for the tiny heads of the screws that hold the cam motor to its assembly).
  • Tiny slot screw drivers 1mm (E) and 3mm (D) or so (to open and close the motor respectively).
  • Lubricant for low speed plastic gears. I use Robbe 5532, which I bought at a model kit store. You can also try to get your hand on the Nakamichi recommended Molykote X5-6020 grease, which I found in cans of 1kg only, so that's going to be expensive.
  • Ball bearing grease (optional).
  • 9 volt battery, or another 6 to 9 volt DC source, so we can test and run the motor.
  • Drill machine with a 1 mm drill bit (optional, to drill holes into the back of the motor, so it will be easier to spray some kind of contact cleaner into the motor in the future, if required.
  • Some kind of contact cleaner (not in the picture). I understand that in the Americas people recommend Deoxit, but as this isn't sold in Europe, I can't tell how well it works. For my European readers, I recommend either Contact Cleaner 390 (by Kontakt Chemie), or even better, a combination of Kontakt 60, Kontakt WL and Kontakt 61 (please do not use Kontakt 60 alone, as this is very agressive stuff that will make matters worse for your motor in the long run if you do not remove it after use).
  • A pair of tweezers (not in the picture) to remove screws and other parts, and to put them back (see note below on using magnetized screwdrivers).
  • Tie wraps (optional), to tie back all wiring in the deck after the repair.

A note on using magnetized screwdrivers

Magnetized screwdrivers are handy, because it makes it easier to remove screws. However, I have been told that when a magmetized screwdriver touches one of the heads or capstan, or even comes close, this might magnetize the deck causing noise and distortion during recording. At time of writing, I do not know if this can be fixed by using a head demagnetizer. I therefore recommend that you do not use magnetized screwdrivers anywhere close to the heads.


Lets get to work

  • First thing you do is unplug your deck from the mains power, as well as anything else. Then, open the cabinet by removing the four screws on the sides, and remove the cover.

    (optional: remove the bottom cover plate from the cabinet, which will make it easier to remove and return the mechanism later).
  • Remove screw A, then unplug connectors B. C, D (record/playback head) and E (erase head, this connector is not on the main board, but on the vertical board on the right). Follow all the disconnected cables (that all lead to the mechnism) and cut all tie wraps that keep these cables in place. Make sure that you don't accidentally cut any wires when removing the tie wraps.

    (Note: in the BX-100, connector D is turned 90 degrees).
  • Remove the little screw in the middle on the upper side, and the two screws in the bottom, as indicated in the pictures. This will allow you to remove the mechanism later.
  • Remove the counter belt from the counter wheel, don't worry about how it's secured on the other side.

    (Note: this doesn't apply to the BX-150).
  • Now take out the mechanism by pulling it backwards. You might have to turn it a bit. Just experiment, but do not force anything! After taking it out, move the cabinet to some safe place, we won't be needing it for a while.
  • We now have only the mechanism on our desk. Remove the two black screws, and then remove the back cover plate.
  • This is what the front side of the mechism looks like. Yours might actually look different, showing a so called idler wheel with a rubber tire on it. The idler wheel rubber tire is a common cause of another problem (take-up reels not turning properly), but it my deck the idler system has been replaced with a gear system during a repair. This gear system became standard starting with the CR-1.

    Now keep the mechnism level with your desk, and remove the screw shown in the picture. Next, open the cassette holder by pressing the lever on the far left:
  • Slide out the metal 'head base hold plate' as shown in the picture, but make sure the metal ball under it doesn't roll away.
  • Using tweezers, take out the metal ball A, next remove screw B.
  • Close the cassette holder if it's open and turn over the mechanism. Remove screws C and D, and just give screws A and B some slack by giving them two turns each, but do not remove them. Then tilt metal plate E with your left hand, and remove the cam motor assembly with your right hand as indicated by the arrow:
  • Notice how Cam wheel (B) is positioned relative to the leaf switches (A). After the motor has been cleaned, the cam wheel must be returned into this position, or it will get difficult to return the cam motor assembly into the mechanism.

    Next, gently lift up the leaf switches and pull the cam wheel out:

    (Note: the cam wheel might have a different position in other models than the BX100/125/150, so make sure you make proper note of it).
  • Gently remove worm wheel C from the motor axis by holding a slot screw driver between the wheel and the motor case, pushing off the wheel with the screw diver. careful, or you might need to look for the wheel at the other end of the room!

    Next, remove screws A and B with the tiny screw driver. Use a decent screw driver with a handle that offers decent grip, to prevent the screw heads from being damaged:
  • Remove the mu-metal shield. You might have to cut the label, and sometimes the mu-metal sticks to the motor case. You might need to apply a little force to get it off, but it helps to turn it clockwise (or counterclockwise, depending on how the mu-metal wasput on the motor), so the strain is decreased. Be carefull not to damage the wiring to the motor:
  • Using the handle of a screwdriver, tap against the case of the motor, and turn the axis around a few times. This will loosen the motor. Now using the 9 volt battery (or a similar power source), let the motor runs for a minute or so, so oxidation is removed from the carbon brushes by means of friction:
  • Using a tiny slot screwdriver, bend out the two metal pins, one on each side, just enough to be able to take the contents out of the case:
  • Now this is very important:

    DO NOT PULL OUT THE PLASTIC PART FROM THE METAL CASE. THIS MIGHT RESULT IN THE CARBON BRUSHES BREAKING OFF, RENDERING YOUR MOTOR USELESS!


    Instead, holding the metal case, push the axis on a firm surface, thus pushing out the contents from the case. When pushed out as far as possible, take out the so called rotor, still attached to the plastic base. You might need to improvise here with a screwdriver:
  • With a small screw driver, lift up one of the metal pins (that hold the carbon brushes), then gently take the rotor off the plastic base, make sure you don't break anything on the metal pin on the other side:
  • Now that the rotor and the plastic base have been separated, you can clearly see that there is a lot of dirt on the contact surfaces. You can probably imagine that spraying some contact cleaner from the outside does not perform a proper cleaning job.

    Now spray a tiny bit of contact cleaner onto the so-called commutator (as indicated by the arrow), as well as onto the two tiny carbon brushes (as indicated by the two little circles). You can use Deoxit, Contact Cleaner 390 or Kontakt 60 for that. Now let it sit for a couple of minutes and do its magic.
  • Meanwhile, clean the cam and worm wheels with a little water and mild soap and some kind of brush (e.g. tooth brush), removing old and dried lubricant, but only if you intend to relubricate them later on. Make sure you dry these wheels thoroughly.
  • Using Q-tips, gently clean the commutator of the rotor as well as the carbon brushes. If you have used an agressive spray such as Kontakt 60, please also rinse with Kontakt WL spray first:
  • Optional step: drill two tiny holes into the plastic base, so it will be easier to spray some kind of contact cleaner into the motor, should that become necessary in the future. Be sure to drill the holes in places that don't damage anything:

  • The carbon brushes are worn by usage, and therefore might apply less pressure on the commutator. To make them apply more pressure, bend each of the metal pin inwards to the center using a srewdriver, as indicated by the arrows. This will really make a difference:
  • Now using a small screwdriver to bend one of the metal pins a bit, gently put the rotor back on the plastic base. After that, spray a small amount of contact spray, either Deoxit, Contact Cleaner 390 or even better Kontakt 61, on the commutator. (Note: NOT KONTAKT 60!). This will provide lubrication as well as protection against oxidation. Then, return the rotor into the metal case.

    Before closing the motor, test it to see it runs with the 9V battery, or another similar power source. Let it run for a minute or so, then reverse the battery polarity to have the motor spin the other way. This will 'grind' the carbon brushes again:
  • Using a slot screwdriver, close the motor case by bending the two pins inwards:
  • Return the mu-metal strip to the motor case:
  • Next, we're going to clean the leaf switches of the cam wheel. Spray a tiny amount of contact cleaner onto the contacts (be sure not to spray on anything else, such as the cam wheel axis), and let it work its magic for a couple of minutes:
  • Drench a piece of cardboard paper in contact cleaner, and rub it between the switches. After that, remove all dirt and cleaning spray residues by gently rubbing a Q-tip between the switches, it helps if you also moisten them with cleaning alcohol. Then again spray a tiny amount of contact cleaner (Deoxit, Contact Cleaner 390 or Kontakt 61, but not Kontakt 60) onto the contacts:
  • Next, reassemble the cam motor assembly by pushing the worm wheel onto the axis and screwing the motor onto the assembly. Then, apply a little lubricant to the cam and worm wheels:
  • Return the cam wheel(B) to the assembly, making sure it's in the right position. You will need to gently lift the leaf switches (A):

    (Note: this picture shows the proper position for the BX100/125/150, but other models might require other positions).
  • Return the cam motor assembly to the mechanism. Axis A needs to go in hole B. You might need to play around with it, sometime the axis will not go into the hole easily. If all goes well, the cam motor assembly is securely in place. Make sure no wires get stuck under one of the metal plates:
  • Returns screws C and D, after that tighten screws A and B:
  • Turn over the mechanism and using Q-tips remove all the lubricant that has been getting stale there for some 20 years or more. Then apply a small amount a fresh ball bearing grease. It's not well visible in the picture, but there is probably a little line worn in by the little metal ball:
  • Return tiny screw A, then holding the mechanism level to your desk, return the metal ball B just to the right of the worn line. The ball bearing grease will most likely hold it there:
  • Still holding the mechanism level, return the head base hold plate (A) by sliding it back in, in such a way that the metal ball is grabbed by the open space in the plate. Then return screw B:
  • Open the cassette holder and return the cover plate into position. Make sure it doesn't stick out at the bottom, as indicated by the picture. After that, return the two black screws at the top of the cover plate:
  • Grab hold of the deck's cabinet and return the mechanism in there. While you slide in the mechanism, hold the counter belt with one hand, so you can easily return it to the counter wheel:
  • Do not yet screw the mechanism into place yet. Instead, reconnect connectors B and C to their sockets, but not yet connectors D and E. Also, make sure the wire that is supposed to be screwed to position A is not in contact with anything that might cause a short circuit.

    Then, connect the power cord to a power outlet, but make sure you do not touch anything inside to prevent electric shock. Now turn the deck on by pressing the power button. If it starts producing unexpected sounds, lights or fumes, immediately switch it off again and try to figure out what went wrong (I can't help you with that one though). But if nothing unexpected happens, press the play button: if the cassette holder is closed, the deck should now come to life! Congrats! Experiment a bit by going from play to pause, stop, rewind etc.etc. To test record mode, you will need to insert a recordable cassette.

    Next, switch off power and disconnect the power cord. Reconnect the R/P head cable connector to socket D and erase head cable connector to socket E. Return the grouding cable to position A using the appropriate screw.

    If you wish, you can organize the cables in the deck using tie-wraps.
  • Secure the mechanism by returning the three screws that hold it in place. Close the cabinet with the top cover and, if you removed it at some stage, the bottom plate.
  • That was all. Now clean the heads, capstan and pinch roller, demagnetize them if you own a head demagnetizer.
  • Happy playing! I recommend that you operate your deck frequently, if only for the purpose of keeping the cam motor carbon brushes from oxidizing again. You don't actually have to listen to music, just press play/stop a few times.

Links

  • Andy’s repairs: cr7 control motor: similar procedure for the CR-7 deck, only Andy doesn't take his cam motor apart. I integrated some of his ideas into my instructions, my gratitude to Andy for that.
  • Scott's Nak FAQ: rich resource of technical information of Nakamichi decks.

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© 2012 Pieter Mol

Disclaimer: All information on this page is provided on an as-is basis with no warranty of any kind. Using this information is at your own risk.