Nakamichi BX100E Capstan Motor - UK Vintage Radio Repair and Restoration Discussion Forum

Takapuna · 7th Apr 2020, 9:11 pm

This is a deck I'm repairing for a friend. It's a Nakamichi BX100E and during soak testing after belt and idler tyre replacement there was suddenly a very loud screeching sound and a reduction in tape speed. The sound puts in an appearance after anything from a couple of minutes to an hour or more and is obviously coming from a distressed capstan motor which can be felt to vibrate in sympathy.

Thinking that a trace of lubricant on the exposed motor shaft might help, I used one of those bent spiky soldering/de-soldering tools to land the smallest drop precisely where motor shaft protrudes from the bush. I rested the shaft of the metal tool on the motor base plate and was surprised to see sparks drawn as I touched the sharp end complete with oil against the rotating motor shaft.

Measuring between the rotating pulley (yes!) and chassis gives a reading of around 5.6Vdc. This is only present when the motor is on. The supply to the motor on the +ve wire is 11.4V.

So I have two questions please:

1). Does this indicate a faulty motor? It may seem to be a silly question with an obvious answer of YES, but there is sufficient electrical insulation by virtue of the motor being rubber-mounted inside its outer casing and another insulating set of grommets from the motor plate to the grounded plate on which it is mounted to allow this voltage to persist. The drive belt is rubber of course and there are no gears to provide a conductive path. Off the top of my head I can't envisage a fault that might lead to this situation unless 5.6V is the motor supply post internal regulator board, assuming it has one, and this is hot-shorted to the motor case.

2). Are these common motors, in spite of the Nakamichi branding, or is it worth my time to carefully apply the Dremmel in an effort to "un-swage" it and see if it can be repaired?

(According to that well-known law, I've just left the deck in Play mode for the last two hours or more whilst writing this and it has been behaving...we'll see)

Thanks for any thoughts and guidance.

Phil
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paulsherwin · 7th Apr 2020, 9:35 pm

This is a Sankyo mechanism, but I suspect NOS replacement motors aren't available. If I were you I'd try everything to fix the original motor, even at the risk of wrecking it.

These are autoreverse decks, and a lot spent their lives in pubs and cafes playing the same tape over and over. You may be able to find a scrap one with worn heads.

Although these are nice enough mid market decks, they aren't 'classic' Naks and it's not worth spending lots of time and money on them if they're just worn out.

Takapuna · 8th Apr 2020, 12:10 pm

Thanks Paul,

The motor has remained quiet for several hours since posting. Tape speed seems to be OK although I haven't measured it accurately. Positive voltage on motor spindle is still present. I don't think that a miniscule amount of oil is the real answer but I'll give it a longer soak test.

The example in front of me is not an auto-reverse deck however.

Phil

paulsherwin · 8th Apr 2020, 12:43 pm

Sorry, you're right, it doesn't have full autoreverse. It optionally plays the same side of the tape repeatedly.

7th Apr 2020, 9:11 pm	#1
Takapuna Tetrode Join Date: Jul 2009 Location: Derby, Derbyshire, UK. Posts: 52	Nakamichi BX100E Capstan Motor This is a deck I'm repairing for a friend. It's a Nakamichi BX100E and during soak testing after belt and idler tyre replacement there was suddenly a very loud screeching sound and a reduction in tape speed. The sound puts in an appearance after anything from a couple of minutes to an hour or more and is obviously coming from a distressed capstan motor which can be felt to vibrate in sympathy. Thinking that a trace of lubricant on the exposed motor shaft might help, I used one of those bent spiky soldering/de-soldering tools to land the smallest drop precisely where motor shaft protrudes from the bush. I rested the shaft of the metal tool on the motor base plate and was surprised to see sparks drawn as I touched the sharp end complete with oil against the rotating motor shaft. Measuring between the rotating pulley (yes!) and chassis gives a reading of around 5.6Vdc. This is only present when the motor is on. The supply to the motor on the +ve wire is 11.4V. So I have two questions please: 1). Does this indicate a faulty motor? It may seem to be a silly question with an obvious answer of YES, but there is sufficient electrical insulation by virtue of the motor being rubber-mounted inside its outer casing and another insulating set of grommets from the motor plate to the grounded plate on which it is mounted to allow this voltage to persist. The drive belt is rubber of course and there are no gears to provide a conductive path. Off the top of my head I can't envisage a fault that might lead to this situation unless 5.6V is the motor supply post internal regulator board, assuming it has one, and this is hot-shorted to the motor case. 2). Are these common motors, in spite of the Nakamichi branding, or is it worth my time to carefully apply the Dremmel in an effort to "un-swage" it and see if it can be repaired? (According to that well-known law, I've just left the deck in Play mode for the last two hours or more whilst writing this and it has been behaving...we'll see) Thanks for any thoughts and guidance. Phil ----

7th Apr 2020, 9:35 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 26,772	Re: Nakamichi BX100E Capstan Motor This is a Sankyo mechanism, but I suspect NOS replacement motors aren't available. If I were you I'd try everything to fix the original motor, even at the risk of wrecking it. These are autoreverse decks, and a lot spent their lives in pubs and cafes playing the same tape over and over. You may be able to find a scrap one with worn heads. Although these are nice enough mid market decks, they aren't 'classic' Naks and it's not worth spending lots of time and money on them if they're just worn out.

8th Apr 2020, 12:10 pm	#3
Takapuna Tetrode Join Date: Jul 2009 Location: Derby, Derbyshire, UK. Posts: 52	Re: Nakamichi BX100E Capstan Motor Thanks Paul, The motor has remained quiet for several hours since posting. Tape speed seems to be OK although I haven't measured it accurately. Positive voltage on motor spindle is still present. I don't think that a miniscule amount of oil is the real answer but I'll give it a longer soak test. The example in front of me is not an auto-reverse deck however. Phil

8th Apr 2020, 12:43 pm	#4
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 26,772	Re: Nakamichi BX100E Capstan Motor Sorry, you're right, it doesn't have full autoreverse. It optionally plays the same side of the tape repeatedly.