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Old 12-12-2008, 05:15 AM
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Repairing a Nakamichi BX300 Control Function Motor

Repairing a Nakamichi BX300 Control Function Motor

As discussed in my previous post I decided to have a go at restoring the control function motor as it had developed a dead spot on the armature causing failure to respond to any of the button press commands.
Some research on the net yielded Scott Johnson's excellent Nak FAQ (hope Scott does not mind me pinching this)

Sankyo Transport Control Motor Problems
The motor used in Sankyo transport decks is a major source of problems in these aging decks. The problem is seen as a deck that seems to not respond to front panel controls (play, stop, rewind, etc.) and on some decks where the transport mode lights flash after an attempted mode change. This is caused by a dead spot that has formed on the control motor stator. A short term fix is to open the deck and give the motor shaft a little nudge. This usually gets it out of that dead spot, but, it will get stuck again. Some people have had success with spraying Caig Labs, DeoxIT into the holes on the back of the motor and cycling the deck through the modes several times. A better solution is to remove the motor from the transport and after spraying in the DeoxIT to let it run for several minutes using an external power source between 4-9 Volts. This will help the motor brushed to scrap away the carbon in the dead spot. A more permanent solution is to disassemble the motor and use very fine grit sandpaper or steel wool to clean the stator while spinning the thing with and electric drill. Apply some DeoxIT and reassemble. There is one more possible solution. Replace the motor. Now these motors are no longer available from Nakamichi, but, two suitable replacements have been found that will require a few minutes of modification to the deck. The Mabuchi RF-370C-15370 motor from MCM Electronics for $32.65 (out of stock at last check) is a very close substitute. The Johnson RF-370C, P/N 174693 motor from Jameco Robot Store, for $2.49 has a slightly longer shaft, but, it will work fine. The mounting holes are 17mm apart on the motors and 16mm apart on the Nak transport. Take a small rat tail file and elongate the two holes on the transport to mount the new motor.

I decided that the best option for me was to ďremove the motor from the transport and after spraying in the DeoxIT to let it run for several minutes using an external power source between 4-9 Volts. This will help the motor brushes to scrape away the carbon in the dead spotĒ. (Hopefully)

The procedures explained below are to suit The Nakamichi BX300 deck but can possibly help with other Nak decks with the Sankyo transports. The BX300 is relatively easy as it does not require much disassembly and you donít need to disturb the wiring loom or cut cable ties etc. There are a few things to watch for (as I discovered), but I will point them out along the way. Please read the text first before pulling anything to bits on each step.

Procedure
First step is to remove the outer top cover via the four screws, two in each side. Once you have the cover off, turn the deck upside down and remove the seven Philips head screws that hold the bottom base plate on and remove the base. Remove the cassette cover door.



Remove the four Phillips head screws along the top edge of the front cover and unclip the surround by the press tabs located top and bottom. The surround should now lift free.



Next job is to remove the cassette well back cover plate. The plate is secured by two screws located in the top corners of the plate. Once the screws are out you can tilt the deck forward and the plate will fall loose. Remove the plate.
Note that this step is also what you need to do to get at the Idler tire assembly.







You can now get at the bits we need to look at. The next picture shows the mounting screw for the mode motor mounting bracket. Itís the bottom silver colored screw.

[

Thankfully Nakamichiís designers have placed a hole in the circuit board that enables a screw driver to be placed as in the next photo. You will need to put a bit of pressure on the wiring so be careful that you do not dislodge or stress the loom unduly.



Remove this screw and the screw shown in the next picture (excuse the shitty picture). This screw is just above the take up reel spool.



The mode motor assembly can now be removed up to where you can get at it.
Undo the long screw that holds the leaf switches and remove the leaf switch block. Make sure the gear cam stays in place at this stage.
Use a tissue or similar soaked in DeoxIT and clean the leaf switch contact points. This cleaning on my deck removed a heap of black oxide material. I guess this is a result of arcing between the contact points.





Iím not sure if itís critical but please NOTE the position of the cam wheel for reassembly. I fucked about for an hour or more trying to get all the modes to work before reinstalling the assembly in place and was getting pissed off as I must have tried every combination before I realized that the mechanism wonít work without with out the last arm activated. This is a steel arm that stays with the main mechanism. This arm rides on the last cam of the mode cam wheel. Be careful when reinstalling the assembly that this arm is indeed in the correct place. Once I activated this last arm everything worked perfectly with the gear placed as it was. Iím not sure that this was not just pure luck, so note the position of the cam wheel before you slide it off the shaft and try and get it in the same position when you reassemble.

Once you have the mode cam wheel removed its time to get some DeoxIT into the back of the motor. There are several holes where the wiring goes in and a few others. Give them all a squirt, sit the motor so the liquid will sink in and leave it for 5 minutes to penetrate.

Get a 9V battery and some jumper leads with alligator clips and connect onto the wiring on both ends of the disc ceramic capacitor on the back of the motor. Connect the other ends to the battery. Polarity is not important as you need to spin the motor for 5 minutes in both directions.



Give the motor another dose of DeoxIT and then reassemble the cam wheel and the leaf switch assembly. As mentioned before, be careful when installing the assembly back onto the main transport. Have a good look at where the steel arm rides on the cam and make sure it positions properly.

The rest of the job is basically a reverse of the above. If your deck is slow in rewind and fast forward do the idler tire at the same time. ESL has good instructions on their web site for this procedure.

Comments.
Glad I gave this a go. The BX300 is a fine deck and way too good to be left with a small problem like this making it useless. Armed with this info you may be able to score a CR-7 or similar thatís going for cheap as ďitís brokenĒ. There is actually a CR 7 on aussie ebay at the moment with I suspect just this problem. $300 for a CR 7Ö..tasty. Nah got too many decks as it is.

Cheers
G
  #2  
Old 12-12-2008, 05:44 AM
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Naknut Naknut is offline
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Great "How to fix it" post. Excellent photos and easy to understand instructions. Thanks for sharing.
  #3  
Old 12-12-2008, 06:56 PM
stuwee stuwee is offline
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Quote:
Originally Posted by Naknut View Post
Great "How to fix it" post. Excellent photos and easy to understand instructions. Thanks for sharing.
2nd!! One question, the last pic with the cam wheel, when you say note the position of the wheel and the arm, are you talking about the one closest to the camera?

Great job Graham, and you do have to many decks, you have my address for the overflow...
  #4  
Old 12-12-2008, 07:05 PM
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Quote:
Originally Posted by stuwee View Post
2nd!! One question, the last pic with the cam wheel, when you say note the position of the wheel and the arm, are you talking about the one closest to the camera?

Great job Graham, and you do have to many decks, you have my address for the overflow...
Yeah Stu. That is correct. You need to watch what position the large plastic cam is in. The motor pinion can be anywhere and still work.
  #5  
Old 12-12-2008, 07:56 PM
stuwee stuwee is offline
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Gotcha! just 'n to be sure, mine hasn't started having the 'fits' yet, knock wood (my head)!
  #6  
Old 12-12-2008, 09:45 PM
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There is actually a CR 7 on aussie ebay at the moment with I suspect just this problem. $300 for a CR 7Ö..tasty. Nah got too many decks as it is.

Not any more...This was RossB's deck. I filled Ross in on the problem and he has wisely decided to keep the deck and pulled it from Ebay....I thought I was the only Aussie on tapenuts....now I know I have company here in Aus.
  #7  
Old 01-09-2009, 11:38 PM
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390FE 390FE is offline
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Maintaince

Hi,
Good tech info. I don't know or have this deck but after looking at the pics & reading that Stuwee hasn't had a problem yet. Stuwee may want to do a little preventative maintaince. It looks like there is easy access to the back of the motor without having to remove it. Thus allowing you to shoot in some Caig DeOxit & allowing it to clean while it is still working & you can cycle through functions a bit to work it in. Now you may want to tip the deck on it's side so the DeOxit sprays in better & do some of the function changes as you spray. So you don't have to disassemble later when it stopps to do the cleaning procedure.
Just a thought. No garantee you still won't have to do this removal procedure or it won't cause it to act up making you take it apart. But I would think that would be on the slim side though.

Any thought to this?
  #8  
Old 04-24-2015, 06:31 PM
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modmatthew modmatthew is offline
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Brilliant I have been having issues with my BX300. I thought I was going to have to break open a motor to clean out carbon. This fixed me right up, thank you thank you thank you.
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  #9  
Old 05-07-2015, 06:47 PM
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Hi Modmatthew,
Glad it helped getting your deck fixed
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